Root/kernel/workqueue.c

1/*
2 * kernel/workqueue.c - generic async execution with shared worker pool
3 *
4 * Copyright (C) 2002 Ingo Molnar
5 *
6 * Derived from the taskqueue/keventd code by:
7 * David Woodhouse <dwmw2@infradead.org>
8 * Andrew Morton
9 * Kai Petzke <wpp@marie.physik.tu-berlin.de>
10 * Theodore Ts'o <tytso@mit.edu>
11 *
12 * Made to use alloc_percpu by Christoph Lameter.
13 *
14 * Copyright (C) 2010 SUSE Linux Products GmbH
15 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
16 *
17 * This is the generic async execution mechanism. Work items as are
18 * executed in process context. The worker pool is shared and
19 * automatically managed. There is one worker pool for each CPU and
20 * one extra for works which are better served by workers which are
21 * not bound to any specific CPU.
22 *
23 * Please read Documentation/workqueue.txt for details.
24 */
25
26#include <linux/module.h>
27#include <linux/kernel.h>
28#include <linux/sched.h>
29#include <linux/init.h>
30#include <linux/signal.h>
31#include <linux/completion.h>
32#include <linux/workqueue.h>
33#include <linux/slab.h>
34#include <linux/cpu.h>
35#include <linux/notifier.h>
36#include <linux/kthread.h>
37#include <linux/hardirq.h>
38#include <linux/mempolicy.h>
39#include <linux/freezer.h>
40#include <linux/kallsyms.h>
41#include <linux/debug_locks.h>
42#include <linux/lockdep.h>
43#include <linux/idr.h>
44
45#include "workqueue_sched.h"
46
47enum {
48    /* global_cwq flags */
49    GCWQ_MANAGE_WORKERS = 1 << 0, /* need to manage workers */
50    GCWQ_MANAGING_WORKERS = 1 << 1, /* managing workers */
51    GCWQ_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */
52    GCWQ_FREEZING = 1 << 3, /* freeze in progress */
53    GCWQ_HIGHPRI_PENDING = 1 << 4, /* highpri works on queue */
54
55    /* worker flags */
56    WORKER_STARTED = 1 << 0, /* started */
57    WORKER_DIE = 1 << 1, /* die die die */
58    WORKER_IDLE = 1 << 2, /* is idle */
59    WORKER_PREP = 1 << 3, /* preparing to run works */
60    WORKER_ROGUE = 1 << 4, /* not bound to any cpu */
61    WORKER_REBIND = 1 << 5, /* mom is home, come back */
62    WORKER_CPU_INTENSIVE = 1 << 6, /* cpu intensive */
63    WORKER_UNBOUND = 1 << 7, /* worker is unbound */
64
65    WORKER_NOT_RUNNING = WORKER_PREP | WORKER_ROGUE | WORKER_REBIND |
66                  WORKER_CPU_INTENSIVE | WORKER_UNBOUND,
67
68    /* gcwq->trustee_state */
69    TRUSTEE_START = 0, /* start */
70    TRUSTEE_IN_CHARGE = 1, /* trustee in charge of gcwq */
71    TRUSTEE_BUTCHER = 2, /* butcher workers */
72    TRUSTEE_RELEASE = 3, /* release workers */
73    TRUSTEE_DONE = 4, /* trustee is done */
74
75    BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */
76    BUSY_WORKER_HASH_SIZE = 1 << BUSY_WORKER_HASH_ORDER,
77    BUSY_WORKER_HASH_MASK = BUSY_WORKER_HASH_SIZE - 1,
78
79    MAX_IDLE_WORKERS_RATIO = 4, /* 1/4 of busy can be idle */
80    IDLE_WORKER_TIMEOUT = 300 * HZ, /* keep idle ones for 5 mins */
81
82    MAYDAY_INITIAL_TIMEOUT = HZ / 100 >= 2 ? HZ / 100 : 2,
83                        /* call for help after 10ms
84                           (min two ticks) */
85    MAYDAY_INTERVAL = HZ / 10, /* and then every 100ms */
86    CREATE_COOLDOWN = HZ, /* time to breath after fail */
87    TRUSTEE_COOLDOWN = HZ / 10, /* for trustee draining */
88
89    /*
90     * Rescue workers are used only on emergencies and shared by
91     * all cpus. Give -20.
92     */
93    RESCUER_NICE_LEVEL = -20,
94};
95
96/*
97 * Structure fields follow one of the following exclusion rules.
98 *
99 * I: Modifiable by initialization/destruction paths and read-only for
100 * everyone else.
101 *
102 * P: Preemption protected. Disabling preemption is enough and should
103 * only be modified and accessed from the local cpu.
104 *
105 * L: gcwq->lock protected. Access with gcwq->lock held.
106 *
107 * X: During normal operation, modification requires gcwq->lock and
108 * should be done only from local cpu. Either disabling preemption
109 * on local cpu or grabbing gcwq->lock is enough for read access.
110 * If GCWQ_DISASSOCIATED is set, it's identical to L.
111 *
112 * F: wq->flush_mutex protected.
113 *
114 * W: workqueue_lock protected.
115 */
116
117struct global_cwq;
118
119/*
120 * The poor guys doing the actual heavy lifting. All on-duty workers
121 * are either serving the manager role, on idle list or on busy hash.
122 */
123struct worker {
124    /* on idle list while idle, on busy hash table while busy */
125    union {
126        struct list_head entry; /* L: while idle */
127        struct hlist_node hentry; /* L: while busy */
128    };
129
130    struct work_struct *current_work; /* L: work being processed */
131    struct cpu_workqueue_struct *current_cwq; /* L: current_work's cwq */
132    struct list_head scheduled; /* L: scheduled works */
133    struct task_struct *task; /* I: worker task */
134    struct global_cwq *gcwq; /* I: the associated gcwq */
135    /* 64 bytes boundary on 64bit, 32 on 32bit */
136    unsigned long last_active; /* L: last active timestamp */
137    unsigned int flags; /* X: flags */
138    int id; /* I: worker id */
139    struct work_struct rebind_work; /* L: rebind worker to cpu */
140};
141
142/*
143 * Global per-cpu workqueue. There's one and only one for each cpu
144 * and all works are queued and processed here regardless of their
145 * target workqueues.
146 */
147struct global_cwq {
148    spinlock_t lock; /* the gcwq lock */
149    struct list_head worklist; /* L: list of pending works */
150    unsigned int cpu; /* I: the associated cpu */
151    unsigned int flags; /* L: GCWQ_* flags */
152
153    int nr_workers; /* L: total number of workers */
154    int nr_idle; /* L: currently idle ones */
155
156    /* workers are chained either in the idle_list or busy_hash */
157    struct list_head idle_list; /* X: list of idle workers */
158    struct hlist_head busy_hash[BUSY_WORKER_HASH_SIZE];
159                        /* L: hash of busy workers */
160
161    struct timer_list idle_timer; /* L: worker idle timeout */
162    struct timer_list mayday_timer; /* L: SOS timer for dworkers */
163
164    struct ida worker_ida; /* L: for worker IDs */
165
166    struct task_struct *trustee; /* L: for gcwq shutdown */
167    unsigned int trustee_state; /* L: trustee state */
168    wait_queue_head_t trustee_wait; /* trustee wait */
169    struct worker *first_idle; /* L: first idle worker */
170} ____cacheline_aligned_in_smp;
171
172/*
173 * The per-CPU workqueue. The lower WORK_STRUCT_FLAG_BITS of
174 * work_struct->data are used for flags and thus cwqs need to be
175 * aligned at two's power of the number of flag bits.
176 */
177struct cpu_workqueue_struct {
178    struct global_cwq *gcwq; /* I: the associated gcwq */
179    struct workqueue_struct *wq; /* I: the owning workqueue */
180    int work_color; /* L: current color */
181    int flush_color; /* L: flushing color */
182    int nr_in_flight[WORK_NR_COLORS];
183                        /* L: nr of in_flight works */
184    int nr_active; /* L: nr of active works */
185    int max_active; /* L: max active works */
186    struct list_head delayed_works; /* L: delayed works */
187};
188
189/*
190 * Structure used to wait for workqueue flush.
191 */
192struct wq_flusher {
193    struct list_head list; /* F: list of flushers */
194    int flush_color; /* F: flush color waiting for */
195    struct completion done; /* flush completion */
196};
197
198/*
199 * All cpumasks are assumed to be always set on UP and thus can't be
200 * used to determine whether there's something to be done.
201 */
202#ifdef CONFIG_SMP
203typedef cpumask_var_t mayday_mask_t;
204#define mayday_test_and_set_cpu(cpu, mask) \
205    cpumask_test_and_set_cpu((cpu), (mask))
206#define mayday_clear_cpu(cpu, mask) cpumask_clear_cpu((cpu), (mask))
207#define for_each_mayday_cpu(cpu, mask) for_each_cpu((cpu), (mask))
208#define alloc_mayday_mask(maskp, gfp) zalloc_cpumask_var((maskp), (gfp))
209#define free_mayday_mask(mask) free_cpumask_var((mask))
210#else
211typedef unsigned long mayday_mask_t;
212#define mayday_test_and_set_cpu(cpu, mask) test_and_set_bit(0, &(mask))
213#define mayday_clear_cpu(cpu, mask) clear_bit(0, &(mask))
214#define for_each_mayday_cpu(cpu, mask) if ((cpu) = 0, (mask))
215#define alloc_mayday_mask(maskp, gfp) true
216#define free_mayday_mask(mask) do { } while (0)
217#endif
218
219/*
220 * The externally visible workqueue abstraction is an array of
221 * per-CPU workqueues:
222 */
223struct workqueue_struct {
224    unsigned int flags; /* I: WQ_* flags */
225    union {
226        struct cpu_workqueue_struct __percpu *pcpu;
227        struct cpu_workqueue_struct *single;
228        unsigned long v;
229    } cpu_wq; /* I: cwq's */
230    struct list_head list; /* W: list of all workqueues */
231
232    struct mutex flush_mutex; /* protects wq flushing */
233    int work_color; /* F: current work color */
234    int flush_color; /* F: current flush color */
235    atomic_t nr_cwqs_to_flush; /* flush in progress */
236    struct wq_flusher *first_flusher; /* F: first flusher */
237    struct list_head flusher_queue; /* F: flush waiters */
238    struct list_head flusher_overflow; /* F: flush overflow list */
239
240    mayday_mask_t mayday_mask; /* cpus requesting rescue */
241    struct worker *rescuer; /* I: rescue worker */
242
243    int saved_max_active; /* W: saved cwq max_active */
244    const char *name; /* I: workqueue name */
245#ifdef CONFIG_LOCKDEP
246    struct lockdep_map lockdep_map;
247#endif
248};
249
250struct workqueue_struct *system_wq __read_mostly;
251struct workqueue_struct *system_long_wq __read_mostly;
252struct workqueue_struct *system_nrt_wq __read_mostly;
253struct workqueue_struct *system_unbound_wq __read_mostly;
254struct workqueue_struct *system_freezable_wq __read_mostly;
255EXPORT_SYMBOL_GPL(system_wq);
256EXPORT_SYMBOL_GPL(system_long_wq);
257EXPORT_SYMBOL_GPL(system_nrt_wq);
258EXPORT_SYMBOL_GPL(system_unbound_wq);
259EXPORT_SYMBOL_GPL(system_freezable_wq);
260
261#define CREATE_TRACE_POINTS
262#include <trace/events/workqueue.h>
263
264#define for_each_busy_worker(worker, i, pos, gcwq) \
265    for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++) \
266        hlist_for_each_entry(worker, pos, &gcwq->busy_hash[i], hentry)
267
268static inline int __next_gcwq_cpu(int cpu, const struct cpumask *mask,
269                  unsigned int sw)
270{
271    if (cpu < nr_cpu_ids) {
272        if (sw & 1) {
273            cpu = cpumask_next(cpu, mask);
274            if (cpu < nr_cpu_ids)
275                return cpu;
276        }
277        if (sw & 2)
278            return WORK_CPU_UNBOUND;
279    }
280    return WORK_CPU_NONE;
281}
282
283static inline int __next_wq_cpu(int cpu, const struct cpumask *mask,
284                struct workqueue_struct *wq)
285{
286    return __next_gcwq_cpu(cpu, mask, !(wq->flags & WQ_UNBOUND) ? 1 : 2);
287}
288
289/*
290 * CPU iterators
291 *
292 * An extra gcwq is defined for an invalid cpu number
293 * (WORK_CPU_UNBOUND) to host workqueues which are not bound to any
294 * specific CPU. The following iterators are similar to
295 * for_each_*_cpu() iterators but also considers the unbound gcwq.
296 *
297 * for_each_gcwq_cpu() : possible CPUs + WORK_CPU_UNBOUND
298 * for_each_online_gcwq_cpu() : online CPUs + WORK_CPU_UNBOUND
299 * for_each_cwq_cpu() : possible CPUs for bound workqueues,
300 * WORK_CPU_UNBOUND for unbound workqueues
301 */
302#define for_each_gcwq_cpu(cpu) \
303    for ((cpu) = __next_gcwq_cpu(-1, cpu_possible_mask, 3); \
304         (cpu) < WORK_CPU_NONE; \
305         (cpu) = __next_gcwq_cpu((cpu), cpu_possible_mask, 3))
306
307#define for_each_online_gcwq_cpu(cpu) \
308    for ((cpu) = __next_gcwq_cpu(-1, cpu_online_mask, 3); \
309         (cpu) < WORK_CPU_NONE; \
310         (cpu) = __next_gcwq_cpu((cpu), cpu_online_mask, 3))
311
312#define for_each_cwq_cpu(cpu, wq) \
313    for ((cpu) = __next_wq_cpu(-1, cpu_possible_mask, (wq)); \
314         (cpu) < WORK_CPU_NONE; \
315         (cpu) = __next_wq_cpu((cpu), cpu_possible_mask, (wq)))
316
317#ifdef CONFIG_DEBUG_OBJECTS_WORK
318
319static struct debug_obj_descr work_debug_descr;
320
321static void *work_debug_hint(void *addr)
322{
323    return ((struct work_struct *) addr)->func;
324}
325
326/*
327 * fixup_init is called when:
328 * - an active object is initialized
329 */
330static int work_fixup_init(void *addr, enum debug_obj_state state)
331{
332    struct work_struct *work = addr;
333
334    switch (state) {
335    case ODEBUG_STATE_ACTIVE:
336        cancel_work_sync(work);
337        debug_object_init(work, &work_debug_descr);
338        return 1;
339    default:
340        return 0;
341    }
342}
343
344/*
345 * fixup_activate is called when:
346 * - an active object is activated
347 * - an unknown object is activated (might be a statically initialized object)
348 */
349static int work_fixup_activate(void *addr, enum debug_obj_state state)
350{
351    struct work_struct *work = addr;
352
353    switch (state) {
354
355    case ODEBUG_STATE_NOTAVAILABLE:
356        /*
357         * This is not really a fixup. The work struct was
358         * statically initialized. We just make sure that it
359         * is tracked in the object tracker.
360         */
361        if (test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work))) {
362            debug_object_init(work, &work_debug_descr);
363            debug_object_activate(work, &work_debug_descr);
364            return 0;
365        }
366        WARN_ON_ONCE(1);
367        return 0;
368
369    case ODEBUG_STATE_ACTIVE:
370        WARN_ON(1);
371
372    default:
373        return 0;
374    }
375}
376
377/*
378 * fixup_free is called when:
379 * - an active object is freed
380 */
381static int work_fixup_free(void *addr, enum debug_obj_state state)
382{
383    struct work_struct *work = addr;
384
385    switch (state) {
386    case ODEBUG_STATE_ACTIVE:
387        cancel_work_sync(work);
388        debug_object_free(work, &work_debug_descr);
389        return 1;
390    default:
391        return 0;
392    }
393}
394
395static struct debug_obj_descr work_debug_descr = {
396    .name = "work_struct",
397    .debug_hint = work_debug_hint,
398    .fixup_init = work_fixup_init,
399    .fixup_activate = work_fixup_activate,
400    .fixup_free = work_fixup_free,
401};
402
403static inline void debug_work_activate(struct work_struct *work)
404{
405    debug_object_activate(work, &work_debug_descr);
406}
407
408static inline void debug_work_deactivate(struct work_struct *work)
409{
410    debug_object_deactivate(work, &work_debug_descr);
411}
412
413void __init_work(struct work_struct *work, int onstack)
414{
415    if (onstack)
416        debug_object_init_on_stack(work, &work_debug_descr);
417    else
418        debug_object_init(work, &work_debug_descr);
419}
420EXPORT_SYMBOL_GPL(__init_work);
421
422void destroy_work_on_stack(struct work_struct *work)
423{
424    debug_object_free(work, &work_debug_descr);
425}
426EXPORT_SYMBOL_GPL(destroy_work_on_stack);
427
428#else
429static inline void debug_work_activate(struct work_struct *work) { }
430static inline void debug_work_deactivate(struct work_struct *work) { }
431#endif
432
433/* Serializes the accesses to the list of workqueues. */
434static DEFINE_SPINLOCK(workqueue_lock);
435static LIST_HEAD(workqueues);
436static bool workqueue_freezing; /* W: have wqs started freezing? */
437
438/*
439 * The almighty global cpu workqueues. nr_running is the only field
440 * which is expected to be used frequently by other cpus via
441 * try_to_wake_up(). Put it in a separate cacheline.
442 */
443static DEFINE_PER_CPU(struct global_cwq, global_cwq);
444static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, gcwq_nr_running);
445
446/*
447 * Global cpu workqueue and nr_running counter for unbound gcwq. The
448 * gcwq is always online, has GCWQ_DISASSOCIATED set, and all its
449 * workers have WORKER_UNBOUND set.
450 */
451static struct global_cwq unbound_global_cwq;
452static atomic_t unbound_gcwq_nr_running = ATOMIC_INIT(0); /* always 0 */
453
454static int worker_thread(void *__worker);
455
456static struct global_cwq *get_gcwq(unsigned int cpu)
457{
458    if (cpu != WORK_CPU_UNBOUND)
459        return &per_cpu(global_cwq, cpu);
460    else
461        return &unbound_global_cwq;
462}
463
464static atomic_t *get_gcwq_nr_running(unsigned int cpu)
465{
466    if (cpu != WORK_CPU_UNBOUND)
467        return &per_cpu(gcwq_nr_running, cpu);
468    else
469        return &unbound_gcwq_nr_running;
470}
471
472static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
473                        struct workqueue_struct *wq)
474{
475    if (!(wq->flags & WQ_UNBOUND)) {
476        if (likely(cpu < nr_cpu_ids)) {
477#ifdef CONFIG_SMP
478            return per_cpu_ptr(wq->cpu_wq.pcpu, cpu);
479#else
480            return wq->cpu_wq.single;
481#endif
482        }
483    } else if (likely(cpu == WORK_CPU_UNBOUND))
484        return wq->cpu_wq.single;
485    return NULL;
486}
487
488static unsigned int work_color_to_flags(int color)
489{
490    return color << WORK_STRUCT_COLOR_SHIFT;
491}
492
493static int get_work_color(struct work_struct *work)
494{
495    return (*work_data_bits(work) >> WORK_STRUCT_COLOR_SHIFT) &
496        ((1 << WORK_STRUCT_COLOR_BITS) - 1);
497}
498
499static int work_next_color(int color)
500{
501    return (color + 1) % WORK_NR_COLORS;
502}
503
504/*
505 * A work's data points to the cwq with WORK_STRUCT_CWQ set while the
506 * work is on queue. Once execution starts, WORK_STRUCT_CWQ is
507 * cleared and the work data contains the cpu number it was last on.
508 *
509 * set_work_{cwq|cpu}() and clear_work_data() can be used to set the
510 * cwq, cpu or clear work->data. These functions should only be
511 * called while the work is owned - ie. while the PENDING bit is set.
512 *
513 * get_work_[g]cwq() can be used to obtain the gcwq or cwq
514 * corresponding to a work. gcwq is available once the work has been
515 * queued anywhere after initialization. cwq is available only from
516 * queueing until execution starts.
517 */
518static inline void set_work_data(struct work_struct *work, unsigned long data,
519                 unsigned long flags)
520{
521    BUG_ON(!work_pending(work));
522    atomic_long_set(&work->data, data | flags | work_static(work));
523}
524
525static void set_work_cwq(struct work_struct *work,
526             struct cpu_workqueue_struct *cwq,
527             unsigned long extra_flags)
528{
529    set_work_data(work, (unsigned long)cwq,
530              WORK_STRUCT_PENDING | WORK_STRUCT_CWQ | extra_flags);
531}
532
533static void set_work_cpu(struct work_struct *work, unsigned int cpu)
534{
535    set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, WORK_STRUCT_PENDING);
536}
537
538static void clear_work_data(struct work_struct *work)
539{
540    set_work_data(work, WORK_STRUCT_NO_CPU, 0);
541}
542
543static struct cpu_workqueue_struct *get_work_cwq(struct work_struct *work)
544{
545    unsigned long data = atomic_long_read(&work->data);
546
547    if (data & WORK_STRUCT_CWQ)
548        return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
549    else
550        return NULL;
551}
552
553static struct global_cwq *get_work_gcwq(struct work_struct *work)
554{
555    unsigned long data = atomic_long_read(&work->data);
556    unsigned int cpu;
557
558    if (data & WORK_STRUCT_CWQ)
559        return ((struct cpu_workqueue_struct *)
560            (data & WORK_STRUCT_WQ_DATA_MASK))->gcwq;
561
562    cpu = data >> WORK_STRUCT_FLAG_BITS;
563    if (cpu == WORK_CPU_NONE)
564        return NULL;
565
566    BUG_ON(cpu >= nr_cpu_ids && cpu != WORK_CPU_UNBOUND);
567    return get_gcwq(cpu);
568}
569
570/*
571 * Policy functions. These define the policies on how the global
572 * worker pool is managed. Unless noted otherwise, these functions
573 * assume that they're being called with gcwq->lock held.
574 */
575
576static bool __need_more_worker(struct global_cwq *gcwq)
577{
578    return !atomic_read(get_gcwq_nr_running(gcwq->cpu)) ||
579        gcwq->flags & GCWQ_HIGHPRI_PENDING;
580}
581
582/*
583 * Need to wake up a worker? Called from anything but currently
584 * running workers.
585 */
586static bool need_more_worker(struct global_cwq *gcwq)
587{
588    return !list_empty(&gcwq->worklist) && __need_more_worker(gcwq);
589}
590
591/* Can I start working? Called from busy but !running workers. */
592static bool may_start_working(struct global_cwq *gcwq)
593{
594    return gcwq->nr_idle;
595}
596
597/* Do I need to keep working? Called from currently running workers. */
598static bool keep_working(struct global_cwq *gcwq)
599{
600    atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);
601
602    return !list_empty(&gcwq->worklist) &&
603        (atomic_read(nr_running) <= 1 ||
604         gcwq->flags & GCWQ_HIGHPRI_PENDING);
605}
606
607/* Do we need a new worker? Called from manager. */
608static bool need_to_create_worker(struct global_cwq *gcwq)
609{
610    return need_more_worker(gcwq) && !may_start_working(gcwq);
611}
612
613/* Do I need to be the manager? */
614static bool need_to_manage_workers(struct global_cwq *gcwq)
615{
616    return need_to_create_worker(gcwq) || gcwq->flags & GCWQ_MANAGE_WORKERS;
617}
618
619/* Do we have too many workers and should some go away? */
620static bool too_many_workers(struct global_cwq *gcwq)
621{
622    bool managing = gcwq->flags & GCWQ_MANAGING_WORKERS;
623    int nr_idle = gcwq->nr_idle + managing; /* manager is considered idle */
624    int nr_busy = gcwq->nr_workers - nr_idle;
625
626    return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
627}
628
629/*
630 * Wake up functions.
631 */
632
633/* Return the first worker. Safe with preemption disabled */
634static struct worker *first_worker(struct global_cwq *gcwq)
635{
636    if (unlikely(list_empty(&gcwq->idle_list)))
637        return NULL;
638
639    return list_first_entry(&gcwq->idle_list, struct worker, entry);
640}
641
642/**
643 * wake_up_worker - wake up an idle worker
644 * @gcwq: gcwq to wake worker for
645 *
646 * Wake up the first idle worker of @gcwq.
647 *
648 * CONTEXT:
649 * spin_lock_irq(gcwq->lock).
650 */
651static void wake_up_worker(struct global_cwq *gcwq)
652{
653    struct worker *worker = first_worker(gcwq);
654
655    if (likely(worker))
656        wake_up_process(worker->task);
657}
658
659/**
660 * wq_worker_waking_up - a worker is waking up
661 * @task: task waking up
662 * @cpu: CPU @task is waking up to
663 *
664 * This function is called during try_to_wake_up() when a worker is
665 * being awoken.
666 *
667 * CONTEXT:
668 * spin_lock_irq(rq->lock)
669 */
670void wq_worker_waking_up(struct task_struct *task, unsigned int cpu)
671{
672    struct worker *worker = kthread_data(task);
673
674    if (!(worker->flags & WORKER_NOT_RUNNING))
675        atomic_inc(get_gcwq_nr_running(cpu));
676}
677
678/**
679 * wq_worker_sleeping - a worker is going to sleep
680 * @task: task going to sleep
681 * @cpu: CPU in question, must be the current CPU number
682 *
683 * This function is called during schedule() when a busy worker is
684 * going to sleep. Worker on the same cpu can be woken up by
685 * returning pointer to its task.
686 *
687 * CONTEXT:
688 * spin_lock_irq(rq->lock)
689 *
690 * RETURNS:
691 * Worker task on @cpu to wake up, %NULL if none.
692 */
693struct task_struct *wq_worker_sleeping(struct task_struct *task,
694                       unsigned int cpu)
695{
696    struct worker *worker = kthread_data(task), *to_wakeup = NULL;
697    struct global_cwq *gcwq = get_gcwq(cpu);
698    atomic_t *nr_running = get_gcwq_nr_running(cpu);
699
700    if (worker->flags & WORKER_NOT_RUNNING)
701        return NULL;
702
703    /* this can only happen on the local cpu */
704    BUG_ON(cpu != raw_smp_processor_id());
705
706    /*
707     * The counterpart of the following dec_and_test, implied mb,
708     * worklist not empty test sequence is in insert_work().
709     * Please read comment there.
710     *
711     * NOT_RUNNING is clear. This means that trustee is not in
712     * charge and we're running on the local cpu w/ rq lock held
713     * and preemption disabled, which in turn means that none else
714     * could be manipulating idle_list, so dereferencing idle_list
715     * without gcwq lock is safe.
716     */
717    if (atomic_dec_and_test(nr_running) && !list_empty(&gcwq->worklist))
718        to_wakeup = first_worker(gcwq);
719    return to_wakeup ? to_wakeup->task : NULL;
720}
721
722/**
723 * worker_set_flags - set worker flags and adjust nr_running accordingly
724 * @worker: self
725 * @flags: flags to set
726 * @wakeup: wakeup an idle worker if necessary
727 *
728 * Set @flags in @worker->flags and adjust nr_running accordingly. If
729 * nr_running becomes zero and @wakeup is %true, an idle worker is
730 * woken up.
731 *
732 * CONTEXT:
733 * spin_lock_irq(gcwq->lock)
734 */
735static inline void worker_set_flags(struct worker *worker, unsigned int flags,
736                    bool wakeup)
737{
738    struct global_cwq *gcwq = worker->gcwq;
739
740    WARN_ON_ONCE(worker->task != current);
741
742    /*
743     * If transitioning into NOT_RUNNING, adjust nr_running and
744     * wake up an idle worker as necessary if requested by
745     * @wakeup.
746     */
747    if ((flags & WORKER_NOT_RUNNING) &&
748        !(worker->flags & WORKER_NOT_RUNNING)) {
749        atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);
750
751        if (wakeup) {
752            if (atomic_dec_and_test(nr_running) &&
753                !list_empty(&gcwq->worklist))
754                wake_up_worker(gcwq);
755        } else
756            atomic_dec(nr_running);
757    }
758
759    worker->flags |= flags;
760}
761
762/**
763 * worker_clr_flags - clear worker flags and adjust nr_running accordingly
764 * @worker: self
765 * @flags: flags to clear
766 *
767 * Clear @flags in @worker->flags and adjust nr_running accordingly.
768 *
769 * CONTEXT:
770 * spin_lock_irq(gcwq->lock)
771 */
772static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
773{
774    struct global_cwq *gcwq = worker->gcwq;
775    unsigned int oflags = worker->flags;
776
777    WARN_ON_ONCE(worker->task != current);
778
779    worker->flags &= ~flags;
780
781    /*
782     * If transitioning out of NOT_RUNNING, increment nr_running. Note
783     * that the nested NOT_RUNNING is not a noop. NOT_RUNNING is mask
784     * of multiple flags, not a single flag.
785     */
786    if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
787        if (!(worker->flags & WORKER_NOT_RUNNING))
788            atomic_inc(get_gcwq_nr_running(gcwq->cpu));
789}
790
791/**
792 * busy_worker_head - return the busy hash head for a work
793 * @gcwq: gcwq of interest
794 * @work: work to be hashed
795 *
796 * Return hash head of @gcwq for @work.
797 *
798 * CONTEXT:
799 * spin_lock_irq(gcwq->lock).
800 *
801 * RETURNS:
802 * Pointer to the hash head.
803 */
804static struct hlist_head *busy_worker_head(struct global_cwq *gcwq,
805                       struct work_struct *work)
806{
807    const int base_shift = ilog2(sizeof(struct work_struct));
808    unsigned long v = (unsigned long)work;
809
810    /* simple shift and fold hash, do we need something better? */
811    v >>= base_shift;
812    v += v >> BUSY_WORKER_HASH_ORDER;
813    v &= BUSY_WORKER_HASH_MASK;
814
815    return &gcwq->busy_hash[v];
816}
817
818/**
819 * __find_worker_executing_work - find worker which is executing a work
820 * @gcwq: gcwq of interest
821 * @bwh: hash head as returned by busy_worker_head()
822 * @work: work to find worker for
823 *
824 * Find a worker which is executing @work on @gcwq. @bwh should be
825 * the hash head obtained by calling busy_worker_head() with the same
826 * work.
827 *
828 * CONTEXT:
829 * spin_lock_irq(gcwq->lock).
830 *
831 * RETURNS:
832 * Pointer to worker which is executing @work if found, NULL
833 * otherwise.
834 */
835static struct worker *__find_worker_executing_work(struct global_cwq *gcwq,
836                           struct hlist_head *bwh,
837                           struct work_struct *work)
838{
839    struct worker *worker;
840    struct hlist_node *tmp;
841
842    hlist_for_each_entry(worker, tmp, bwh, hentry)
843        if (worker->current_work == work)
844            return worker;
845    return NULL;
846}
847
848/**
849 * find_worker_executing_work - find worker which is executing a work
850 * @gcwq: gcwq of interest
851 * @work: work to find worker for
852 *
853 * Find a worker which is executing @work on @gcwq. This function is
854 * identical to __find_worker_executing_work() except that this
855 * function calculates @bwh itself.
856 *
857 * CONTEXT:
858 * spin_lock_irq(gcwq->lock).
859 *
860 * RETURNS:
861 * Pointer to worker which is executing @work if found, NULL
862 * otherwise.
863 */
864static struct worker *find_worker_executing_work(struct global_cwq *gcwq,
865                         struct work_struct *work)
866{
867    return __find_worker_executing_work(gcwq, busy_worker_head(gcwq, work),
868                        work);
869}
870
871/**
872 * gcwq_determine_ins_pos - find insertion position
873 * @gcwq: gcwq of interest
874 * @cwq: cwq a work is being queued for
875 *
876 * A work for @cwq is about to be queued on @gcwq, determine insertion
877 * position for the work. If @cwq is for HIGHPRI wq, the work is
878 * queued at the head of the queue but in FIFO order with respect to
879 * other HIGHPRI works; otherwise, at the end of the queue. This
880 * function also sets GCWQ_HIGHPRI_PENDING flag to hint @gcwq that
881 * there are HIGHPRI works pending.
882 *
883 * CONTEXT:
884 * spin_lock_irq(gcwq->lock).
885 *
886 * RETURNS:
887 * Pointer to inserstion position.
888 */
889static inline struct list_head *gcwq_determine_ins_pos(struct global_cwq *gcwq,
890                           struct cpu_workqueue_struct *cwq)
891{
892    struct work_struct *twork;
893
894    if (likely(!(cwq->wq->flags & WQ_HIGHPRI)))
895        return &gcwq->worklist;
896
897    list_for_each_entry(twork, &gcwq->worklist, entry) {
898        struct cpu_workqueue_struct *tcwq = get_work_cwq(twork);
899
900        if (!(tcwq->wq->flags & WQ_HIGHPRI))
901            break;
902    }
903
904    gcwq->flags |= GCWQ_HIGHPRI_PENDING;
905    return &twork->entry;
906}
907
908/**
909 * insert_work - insert a work into gcwq
910 * @cwq: cwq @work belongs to
911 * @work: work to insert
912 * @head: insertion point
913 * @extra_flags: extra WORK_STRUCT_* flags to set
914 *
915 * Insert @work which belongs to @cwq into @gcwq after @head.
916 * @extra_flags is or'd to work_struct flags.
917 *
918 * CONTEXT:
919 * spin_lock_irq(gcwq->lock).
920 */
921static void insert_work(struct cpu_workqueue_struct *cwq,
922            struct work_struct *work, struct list_head *head,
923            unsigned int extra_flags)
924{
925    struct global_cwq *gcwq = cwq->gcwq;
926
927    /* we own @work, set data and link */
928    set_work_cwq(work, cwq, extra_flags);
929
930    /*
931     * Ensure that we get the right work->data if we see the
932     * result of list_add() below, see try_to_grab_pending().
933     */
934    smp_wmb();
935
936    list_add_tail(&work->entry, head);
937
938    /*
939     * Ensure either worker_sched_deactivated() sees the above
940     * list_add_tail() or we see zero nr_running to avoid workers
941     * lying around lazily while there are works to be processed.
942     */
943    smp_mb();
944
945    if (__need_more_worker(gcwq))
946        wake_up_worker(gcwq);
947}
948
949/*
950 * Test whether @work is being queued from another work executing on the
951 * same workqueue. This is rather expensive and should only be used from
952 * cold paths.
953 */
954static bool is_chained_work(struct workqueue_struct *wq)
955{
956    unsigned long flags;
957    unsigned int cpu;
958
959    for_each_gcwq_cpu(cpu) {
960        struct global_cwq *gcwq = get_gcwq(cpu);
961        struct worker *worker;
962        struct hlist_node *pos;
963        int i;
964
965        spin_lock_irqsave(&gcwq->lock, flags);
966        for_each_busy_worker(worker, i, pos, gcwq) {
967            if (worker->task != current)
968                continue;
969            spin_unlock_irqrestore(&gcwq->lock, flags);
970            /*
971             * I'm @worker, no locking necessary. See if @work
972             * is headed to the same workqueue.
973             */
974            return worker->current_cwq->wq == wq;
975        }
976        spin_unlock_irqrestore(&gcwq->lock, flags);
977    }
978    return false;
979}
980
981static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
982             struct work_struct *work)
983{
984    struct global_cwq *gcwq;
985    struct cpu_workqueue_struct *cwq;
986    struct list_head *worklist;
987    unsigned int work_flags;
988    unsigned long flags;
989
990    debug_work_activate(work);
991
992    /* if dying, only works from the same workqueue are allowed */
993    if (unlikely(wq->flags & WQ_DYING) &&
994        WARN_ON_ONCE(!is_chained_work(wq)))
995        return;
996
997    /* determine gcwq to use */
998    if (!(wq->flags & WQ_UNBOUND)) {
999        struct global_cwq *last_gcwq;
1000
1001        if (unlikely(cpu == WORK_CPU_UNBOUND))
1002            cpu = raw_smp_processor_id();
1003
1004        /*
1005         * It's multi cpu. If @wq is non-reentrant and @work
1006         * was previously on a different cpu, it might still
1007         * be running there, in which case the work needs to
1008         * be queued on that cpu to guarantee non-reentrance.
1009         */
1010        gcwq = get_gcwq(cpu);
1011        if (wq->flags & WQ_NON_REENTRANT &&
1012            (last_gcwq = get_work_gcwq(work)) && last_gcwq != gcwq) {
1013            struct worker *worker;
1014
1015            spin_lock_irqsave(&last_gcwq->lock, flags);
1016
1017            worker = find_worker_executing_work(last_gcwq, work);
1018
1019            if (worker && worker->current_cwq->wq == wq)
1020                gcwq = last_gcwq;
1021            else {
1022                /* meh... not running there, queue here */
1023                spin_unlock_irqrestore(&last_gcwq->lock, flags);
1024                spin_lock_irqsave(&gcwq->lock, flags);
1025            }
1026        } else
1027            spin_lock_irqsave(&gcwq->lock, flags);
1028    } else {
1029        gcwq = get_gcwq(WORK_CPU_UNBOUND);
1030        spin_lock_irqsave(&gcwq->lock, flags);
1031    }
1032
1033    /* gcwq determined, get cwq and queue */
1034    cwq = get_cwq(gcwq->cpu, wq);
1035    trace_workqueue_queue_work(cpu, cwq, work);
1036
1037    BUG_ON(!list_empty(&work->entry));
1038
1039    cwq->nr_in_flight[cwq->work_color]++;
1040    work_flags = work_color_to_flags(cwq->work_color);
1041
1042    if (likely(cwq->nr_active < cwq->max_active)) {
1043        trace_workqueue_activate_work(work);
1044        cwq->nr_active++;
1045        worklist = gcwq_determine_ins_pos(gcwq, cwq);
1046    } else {
1047        work_flags |= WORK_STRUCT_DELAYED;
1048        worklist = &cwq->delayed_works;
1049    }
1050
1051    insert_work(cwq, work, worklist, work_flags);
1052
1053    spin_unlock_irqrestore(&gcwq->lock, flags);
1054}
1055
1056/**
1057 * queue_work - queue work on a workqueue
1058 * @wq: workqueue to use
1059 * @work: work to queue
1060 *
1061 * Returns 0 if @work was already on a queue, non-zero otherwise.
1062 *
1063 * We queue the work to the CPU on which it was submitted, but if the CPU dies
1064 * it can be processed by another CPU.
1065 */
1066int queue_work(struct workqueue_struct *wq, struct work_struct *work)
1067{
1068    int ret;
1069
1070    ret = queue_work_on(get_cpu(), wq, work);
1071    put_cpu();
1072
1073    return ret;
1074}
1075EXPORT_SYMBOL_GPL(queue_work);
1076
1077/**
1078 * queue_work_on - queue work on specific cpu
1079 * @cpu: CPU number to execute work on
1080 * @wq: workqueue to use
1081 * @work: work to queue
1082 *
1083 * Returns 0 if @work was already on a queue, non-zero otherwise.
1084 *
1085 * We queue the work to a specific CPU, the caller must ensure it
1086 * can't go away.
1087 */
1088int
1089queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
1090{
1091    int ret = 0;
1092
1093    if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
1094        __queue_work(cpu, wq, work);
1095        ret = 1;
1096    }
1097    return ret;
1098}
1099EXPORT_SYMBOL_GPL(queue_work_on);
1100
1101static void delayed_work_timer_fn(unsigned long __data)
1102{
1103    struct delayed_work *dwork = (struct delayed_work *)__data;
1104    struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);
1105
1106    __queue_work(smp_processor_id(), cwq->wq, &dwork->work);
1107}
1108
1109/**
1110 * queue_delayed_work - queue work on a workqueue after delay
1111 * @wq: workqueue to use
1112 * @dwork: delayable work to queue
1113 * @delay: number of jiffies to wait before queueing
1114 *
1115 * Returns 0 if @work was already on a queue, non-zero otherwise.
1116 */
1117int queue_delayed_work(struct workqueue_struct *wq,
1118            struct delayed_work *dwork, unsigned long delay)
1119{
1120    if (delay == 0)
1121        return queue_work(wq, &dwork->work);
1122
1123    return queue_delayed_work_on(-1, wq, dwork, delay);
1124}
1125EXPORT_SYMBOL_GPL(queue_delayed_work);
1126
1127/**
1128 * queue_delayed_work_on - queue work on specific CPU after delay
1129 * @cpu: CPU number to execute work on
1130 * @wq: workqueue to use
1131 * @dwork: work to queue
1132 * @delay: number of jiffies to wait before queueing
1133 *
1134 * Returns 0 if @work was already on a queue, non-zero otherwise.
1135 */
1136int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
1137            struct delayed_work *dwork, unsigned long delay)
1138{
1139    int ret = 0;
1140    struct timer_list *timer = &dwork->timer;
1141    struct work_struct *work = &dwork->work;
1142
1143    if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
1144        unsigned int lcpu;
1145
1146        BUG_ON(timer_pending(timer));
1147        BUG_ON(!list_empty(&work->entry));
1148
1149        timer_stats_timer_set_start_info(&dwork->timer);
1150
1151        /*
1152         * This stores cwq for the moment, for the timer_fn.
1153         * Note that the work's gcwq is preserved to allow
1154         * reentrance detection for delayed works.
1155         */
1156        if (!(wq->flags & WQ_UNBOUND)) {
1157            struct global_cwq *gcwq = get_work_gcwq(work);
1158
1159            if (gcwq && gcwq->cpu != WORK_CPU_UNBOUND)
1160                lcpu = gcwq->cpu;
1161            else
1162                lcpu = raw_smp_processor_id();
1163        } else
1164            lcpu = WORK_CPU_UNBOUND;
1165
1166        set_work_cwq(work, get_cwq(lcpu, wq), 0);
1167
1168        timer->expires = jiffies + delay;
1169        timer->data = (unsigned long)dwork;
1170        timer->function = delayed_work_timer_fn;
1171
1172        if (unlikely(cpu >= 0))
1173            add_timer_on(timer, cpu);
1174        else
1175            add_timer(timer);
1176        ret = 1;
1177    }
1178    return ret;
1179}
1180EXPORT_SYMBOL_GPL(queue_delayed_work_on);
1181
1182/**
1183 * worker_enter_idle - enter idle state
1184 * @worker: worker which is entering idle state
1185 *
1186 * @worker is entering idle state. Update stats and idle timer if
1187 * necessary.
1188 *
1189 * LOCKING:
1190 * spin_lock_irq(gcwq->lock).
1191 */
1192static void worker_enter_idle(struct worker *worker)
1193{
1194    struct global_cwq *gcwq = worker->gcwq;
1195
1196    BUG_ON(worker->flags & WORKER_IDLE);
1197    BUG_ON(!list_empty(&worker->entry) &&
1198           (worker->hentry.next || worker->hentry.pprev));
1199
1200    /* can't use worker_set_flags(), also called from start_worker() */
1201    worker->flags |= WORKER_IDLE;
1202    gcwq->nr_idle++;
1203    worker->last_active = jiffies;
1204
1205    /* idle_list is LIFO */
1206    list_add(&worker->entry, &gcwq->idle_list);
1207
1208    if (likely(!(worker->flags & WORKER_ROGUE))) {
1209        if (too_many_workers(gcwq) && !timer_pending(&gcwq->idle_timer))
1210            mod_timer(&gcwq->idle_timer,
1211                  jiffies + IDLE_WORKER_TIMEOUT);
1212    } else
1213        wake_up_all(&gcwq->trustee_wait);
1214
1215    /* sanity check nr_running */
1216    WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
1217             atomic_read(get_gcwq_nr_running(gcwq->cpu)));
1218}
1219
1220/**
1221 * worker_leave_idle - leave idle state
1222 * @worker: worker which is leaving idle state
1223 *
1224 * @worker is leaving idle state. Update stats.
1225 *
1226 * LOCKING:
1227 * spin_lock_irq(gcwq->lock).
1228 */
1229static void worker_leave_idle(struct worker *worker)
1230{
1231    struct global_cwq *gcwq = worker->gcwq;
1232
1233    BUG_ON(!(worker->flags & WORKER_IDLE));
1234    worker_clr_flags(worker, WORKER_IDLE);
1235    gcwq->nr_idle--;
1236    list_del_init(&worker->entry);
1237}
1238
1239/**
1240 * worker_maybe_bind_and_lock - bind worker to its cpu if possible and lock gcwq
1241 * @worker: self
1242 *
1243 * Works which are scheduled while the cpu is online must at least be
1244 * scheduled to a worker which is bound to the cpu so that if they are
1245 * flushed from cpu callbacks while cpu is going down, they are
1246 * guaranteed to execute on the cpu.
1247 *
1248 * This function is to be used by rogue workers and rescuers to bind
1249 * themselves to the target cpu and may race with cpu going down or
1250 * coming online. kthread_bind() can't be used because it may put the
1251 * worker to already dead cpu and set_cpus_allowed_ptr() can't be used
1252 * verbatim as it's best effort and blocking and gcwq may be
1253 * [dis]associated in the meantime.
1254 *
1255 * This function tries set_cpus_allowed() and locks gcwq and verifies
1256 * the binding against GCWQ_DISASSOCIATED which is set during
1257 * CPU_DYING and cleared during CPU_ONLINE, so if the worker enters
1258 * idle state or fetches works without dropping lock, it can guarantee
1259 * the scheduling requirement described in the first paragraph.
1260 *
1261 * CONTEXT:
1262 * Might sleep. Called without any lock but returns with gcwq->lock
1263 * held.
1264 *
1265 * RETURNS:
1266 * %true if the associated gcwq is online (@worker is successfully
1267 * bound), %false if offline.
1268 */
1269static bool worker_maybe_bind_and_lock(struct worker *worker)
1270__acquires(&gcwq->lock)
1271{
1272    struct global_cwq *gcwq = worker->gcwq;
1273    struct task_struct *task = worker->task;
1274
1275    while (true) {
1276        /*
1277         * The following call may fail, succeed or succeed
1278         * without actually migrating the task to the cpu if
1279         * it races with cpu hotunplug operation. Verify
1280         * against GCWQ_DISASSOCIATED.
1281         */
1282        if (!(gcwq->flags & GCWQ_DISASSOCIATED))
1283            set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));
1284
1285        spin_lock_irq(&gcwq->lock);
1286        if (gcwq->flags & GCWQ_DISASSOCIATED)
1287            return false;
1288        if (task_cpu(task) == gcwq->cpu &&
1289            cpumask_equal(&current->cpus_allowed,
1290                  get_cpu_mask(gcwq->cpu)))
1291            return true;
1292        spin_unlock_irq(&gcwq->lock);
1293
1294        /*
1295         * We've raced with CPU hot[un]plug. Give it a breather
1296         * and retry migration. cond_resched() is required here;
1297         * otherwise, we might deadlock against cpu_stop trying to
1298         * bring down the CPU on non-preemptive kernel.
1299         */
1300        cpu_relax();
1301        cond_resched();
1302    }
1303}
1304
1305/*
1306 * Function for worker->rebind_work used to rebind rogue busy workers
1307 * to the associated cpu which is coming back online. This is
1308 * scheduled by cpu up but can race with other cpu hotplug operations
1309 * and may be executed twice without intervening cpu down.
1310 */
1311static void worker_rebind_fn(struct work_struct *work)
1312{
1313    struct worker *worker = container_of(work, struct worker, rebind_work);
1314    struct global_cwq *gcwq = worker->gcwq;
1315
1316    if (worker_maybe_bind_and_lock(worker))
1317        worker_clr_flags(worker, WORKER_REBIND);
1318
1319    spin_unlock_irq(&gcwq->lock);
1320}
1321
1322static struct worker *alloc_worker(void)
1323{
1324    struct worker *worker;
1325
1326    worker = kzalloc(sizeof(*worker), GFP_KERNEL);
1327    if (worker) {
1328        INIT_LIST_HEAD(&worker->entry);
1329        INIT_LIST_HEAD(&worker->scheduled);
1330        INIT_WORK(&worker->rebind_work, worker_rebind_fn);
1331        /* on creation a worker is in !idle && prep state */
1332        worker->flags = WORKER_PREP;
1333    }
1334    return worker;
1335}
1336
1337/**
1338 * create_worker - create a new workqueue worker
1339 * @gcwq: gcwq the new worker will belong to
1340 * @bind: whether to set affinity to @cpu or not
1341 *
1342 * Create a new worker which is bound to @gcwq. The returned worker
1343 * can be started by calling start_worker() or destroyed using
1344 * destroy_worker().
1345 *
1346 * CONTEXT:
1347 * Might sleep. Does GFP_KERNEL allocations.
1348 *
1349 * RETURNS:
1350 * Pointer to the newly created worker.
1351 */
1352static struct worker *create_worker(struct global_cwq *gcwq, bool bind)
1353{
1354    bool on_unbound_cpu = gcwq->cpu == WORK_CPU_UNBOUND;
1355    struct worker *worker = NULL;
1356    int id = -1;
1357
1358    spin_lock_irq(&gcwq->lock);
1359    while (ida_get_new(&gcwq->worker_ida, &id)) {
1360        spin_unlock_irq(&gcwq->lock);
1361        if (!ida_pre_get(&gcwq->worker_ida, GFP_KERNEL))
1362            goto fail;
1363        spin_lock_irq(&gcwq->lock);
1364    }
1365    spin_unlock_irq(&gcwq->lock);
1366
1367    worker = alloc_worker();
1368    if (!worker)
1369        goto fail;
1370
1371    worker->gcwq = gcwq;
1372    worker->id = id;
1373
1374    if (!on_unbound_cpu)
1375        worker->task = kthread_create_on_node(worker_thread,
1376                              worker,
1377                              cpu_to_node(gcwq->cpu),
1378                              "kworker/%u:%d", gcwq->cpu, id);
1379    else
1380        worker->task = kthread_create(worker_thread, worker,
1381                          "kworker/u:%d", id);
1382    if (IS_ERR(worker->task))
1383        goto fail;
1384
1385    /*
1386     * A rogue worker will become a regular one if CPU comes
1387     * online later on. Make sure every worker has
1388     * PF_THREAD_BOUND set.
1389     */
1390    if (bind && !on_unbound_cpu)
1391        kthread_bind(worker->task, gcwq->cpu);
1392    else {
1393        worker->task->flags |= PF_THREAD_BOUND;
1394        if (on_unbound_cpu)
1395            worker->flags |= WORKER_UNBOUND;
1396    }
1397
1398    return worker;
1399fail:
1400    if (id >= 0) {
1401        spin_lock_irq(&gcwq->lock);
1402        ida_remove(&gcwq->worker_ida, id);
1403        spin_unlock_irq(&gcwq->lock);
1404    }
1405    kfree(worker);
1406    return NULL;
1407}
1408
1409/**
1410 * start_worker - start a newly created worker
1411 * @worker: worker to start
1412 *
1413 * Make the gcwq aware of @worker and start it.
1414 *
1415 * CONTEXT:
1416 * spin_lock_irq(gcwq->lock).
1417 */
1418static void start_worker(struct worker *worker)
1419{
1420    worker->flags |= WORKER_STARTED;
1421    worker->gcwq->nr_workers++;
1422    worker_enter_idle(worker);
1423    wake_up_process(worker->task);
1424}
1425
1426/**
1427 * destroy_worker - destroy a workqueue worker
1428 * @worker: worker to be destroyed
1429 *
1430 * Destroy @worker and adjust @gcwq stats accordingly.
1431 *
1432 * CONTEXT:
1433 * spin_lock_irq(gcwq->lock) which is released and regrabbed.
1434 */
1435static void destroy_worker(struct worker *worker)
1436{
1437    struct global_cwq *gcwq = worker->gcwq;
1438    int id = worker->id;
1439
1440    /* sanity check frenzy */
1441    BUG_ON(worker->current_work);
1442    BUG_ON(!list_empty(&worker->scheduled));
1443
1444    if (worker->flags & WORKER_STARTED)
1445        gcwq->nr_workers--;
1446    if (worker->flags & WORKER_IDLE)
1447        gcwq->nr_idle--;
1448
1449    list_del_init(&worker->entry);
1450    worker->flags |= WORKER_DIE;
1451
1452    spin_unlock_irq(&gcwq->lock);
1453
1454    kthread_stop(worker->task);
1455    kfree(worker);
1456
1457    spin_lock_irq(&gcwq->lock);
1458    ida_remove(&gcwq->worker_ida, id);
1459}
1460
1461static void idle_worker_timeout(unsigned long __gcwq)
1462{
1463    struct global_cwq *gcwq = (void *)__gcwq;
1464
1465    spin_lock_irq(&gcwq->lock);
1466
1467    if (too_many_workers(gcwq)) {
1468        struct worker *worker;
1469        unsigned long expires;
1470
1471        /* idle_list is kept in LIFO order, check the last one */
1472        worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
1473        expires = worker->last_active + IDLE_WORKER_TIMEOUT;
1474
1475        if (time_before(jiffies, expires))
1476            mod_timer(&gcwq->idle_timer, expires);
1477        else {
1478            /* it's been idle for too long, wake up manager */
1479            gcwq->flags |= GCWQ_MANAGE_WORKERS;
1480            wake_up_worker(gcwq);
1481        }
1482    }
1483
1484    spin_unlock_irq(&gcwq->lock);
1485}
1486
1487static bool send_mayday(struct work_struct *work)
1488{
1489    struct cpu_workqueue_struct *cwq = get_work_cwq(work);
1490    struct workqueue_struct *wq = cwq->wq;
1491    unsigned int cpu;
1492
1493    if (!(wq->flags & WQ_RESCUER))
1494        return false;
1495
1496    /* mayday mayday mayday */
1497    cpu = cwq->gcwq->cpu;
1498    /* WORK_CPU_UNBOUND can't be set in cpumask, use cpu 0 instead */
1499    if (cpu == WORK_CPU_UNBOUND)
1500        cpu = 0;
1501    if (!mayday_test_and_set_cpu(cpu, wq->mayday_mask))
1502        wake_up_process(wq->rescuer->task);
1503    return true;
1504}
1505
1506static void gcwq_mayday_timeout(unsigned long __gcwq)
1507{
1508    struct global_cwq *gcwq = (void *)__gcwq;
1509    struct work_struct *work;
1510
1511    spin_lock_irq(&gcwq->lock);
1512
1513    if (need_to_create_worker(gcwq)) {
1514        /*
1515         * We've been trying to create a new worker but
1516         * haven't been successful. We might be hitting an
1517         * allocation deadlock. Send distress signals to
1518         * rescuers.
1519         */
1520        list_for_each_entry(work, &gcwq->worklist, entry)
1521            send_mayday(work);
1522    }
1523
1524    spin_unlock_irq(&gcwq->lock);
1525
1526    mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INTERVAL);
1527}
1528
1529/**
1530 * maybe_create_worker - create a new worker if necessary
1531 * @gcwq: gcwq to create a new worker for
1532 *
1533 * Create a new worker for @gcwq if necessary. @gcwq is guaranteed to
1534 * have at least one idle worker on return from this function. If
1535 * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
1536 * sent to all rescuers with works scheduled on @gcwq to resolve
1537 * possible allocation deadlock.
1538 *
1539 * On return, need_to_create_worker() is guaranteed to be false and
1540 * may_start_working() true.
1541 *
1542 * LOCKING:
1543 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
1544 * multiple times. Does GFP_KERNEL allocations. Called only from
1545 * manager.
1546 *
1547 * RETURNS:
1548 * false if no action was taken and gcwq->lock stayed locked, true
1549 * otherwise.
1550 */
1551static bool maybe_create_worker(struct global_cwq *gcwq)
1552__releases(&gcwq->lock)
1553__acquires(&gcwq->lock)
1554{
1555    if (!need_to_create_worker(gcwq))
1556        return false;
1557restart:
1558    spin_unlock_irq(&gcwq->lock);
1559
1560    /* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
1561    mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
1562
1563    while (true) {
1564        struct worker *worker;
1565
1566        worker = create_worker(gcwq, true);
1567        if (worker) {
1568            del_timer_sync(&gcwq->mayday_timer);
1569            spin_lock_irq(&gcwq->lock);
1570            start_worker(worker);
1571            BUG_ON(need_to_create_worker(gcwq));
1572            return true;
1573        }
1574
1575        if (!need_to_create_worker(gcwq))
1576            break;
1577
1578        __set_current_state(TASK_INTERRUPTIBLE);
1579        schedule_timeout(CREATE_COOLDOWN);
1580
1581        if (!need_to_create_worker(gcwq))
1582            break;
1583    }
1584
1585    del_timer_sync(&gcwq->mayday_timer);
1586    spin_lock_irq(&gcwq->lock);
1587    if (need_to_create_worker(gcwq))
1588        goto restart;
1589    return true;
1590}
1591
1592/**
1593 * maybe_destroy_worker - destroy workers which have been idle for a while
1594 * @gcwq: gcwq to destroy workers for
1595 *
1596 * Destroy @gcwq workers which have been idle for longer than
1597 * IDLE_WORKER_TIMEOUT.
1598 *
1599 * LOCKING:
1600 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
1601 * multiple times. Called only from manager.
1602 *
1603 * RETURNS:
1604 * false if no action was taken and gcwq->lock stayed locked, true
1605 * otherwise.
1606 */
1607static bool maybe_destroy_workers(struct global_cwq *gcwq)
1608{
1609    bool ret = false;
1610
1611    while (too_many_workers(gcwq)) {
1612        struct worker *worker;
1613        unsigned long expires;
1614
1615        worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
1616        expires = worker->last_active + IDLE_WORKER_TIMEOUT;
1617
1618        if (time_before(jiffies, expires)) {
1619            mod_timer(&gcwq->idle_timer, expires);
1620            break;
1621        }
1622
1623        destroy_worker(worker);
1624        ret = true;
1625    }
1626
1627    return ret;
1628}
1629
1630/**
1631 * manage_workers - manage worker pool
1632 * @worker: self
1633 *
1634 * Assume the manager role and manage gcwq worker pool @worker belongs
1635 * to. At any given time, there can be only zero or one manager per
1636 * gcwq. The exclusion is handled automatically by this function.
1637 *
1638 * The caller can safely start processing works on false return. On
1639 * true return, it's guaranteed that need_to_create_worker() is false
1640 * and may_start_working() is true.
1641 *
1642 * CONTEXT:
1643 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
1644 * multiple times. Does GFP_KERNEL allocations.
1645 *
1646 * RETURNS:
1647 * false if no action was taken and gcwq->lock stayed locked, true if
1648 * some action was taken.
1649 */
1650static bool manage_workers(struct worker *worker)
1651{
1652    struct global_cwq *gcwq = worker->gcwq;
1653    bool ret = false;
1654
1655    if (gcwq->flags & GCWQ_MANAGING_WORKERS)
1656        return ret;
1657
1658    gcwq->flags &= ~GCWQ_MANAGE_WORKERS;
1659    gcwq->flags |= GCWQ_MANAGING_WORKERS;
1660
1661    /*
1662     * Destroy and then create so that may_start_working() is true
1663     * on return.
1664     */
1665    ret |= maybe_destroy_workers(gcwq);
1666    ret |= maybe_create_worker(gcwq);
1667
1668    gcwq->flags &= ~GCWQ_MANAGING_WORKERS;
1669
1670    /*
1671     * The trustee might be waiting to take over the manager
1672     * position, tell it we're done.
1673     */
1674    if (unlikely(gcwq->trustee))
1675        wake_up_all(&gcwq->trustee_wait);
1676
1677    return ret;
1678}
1679
1680/**
1681 * move_linked_works - move linked works to a list
1682 * @work: start of series of works to be scheduled
1683 * @head: target list to append @work to
1684 * @nextp: out paramter for nested worklist walking
1685 *
1686 * Schedule linked works starting from @work to @head. Work series to
1687 * be scheduled starts at @work and includes any consecutive work with
1688 * WORK_STRUCT_LINKED set in its predecessor.
1689 *
1690 * If @nextp is not NULL, it's updated to point to the next work of
1691 * the last scheduled work. This allows move_linked_works() to be
1692 * nested inside outer list_for_each_entry_safe().
1693 *
1694 * CONTEXT:
1695 * spin_lock_irq(gcwq->lock).
1696 */
1697static void move_linked_works(struct work_struct *work, struct list_head *head,
1698                  struct work_struct **nextp)
1699{
1700    struct work_struct *n;
1701
1702    /*
1703     * Linked worklist will always end before the end of the list,
1704     * use NULL for list head.
1705     */
1706    list_for_each_entry_safe_from(work, n, NULL, entry) {
1707        list_move_tail(&work->entry, head);
1708        if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
1709            break;
1710    }
1711
1712    /*
1713     * If we're already inside safe list traversal and have moved
1714     * multiple works to the scheduled queue, the next position
1715     * needs to be updated.
1716     */
1717    if (nextp)
1718        *nextp = n;
1719}
1720
1721static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
1722{
1723    struct work_struct *work = list_first_entry(&cwq->delayed_works,
1724                            struct work_struct, entry);
1725    struct list_head *pos = gcwq_determine_ins_pos(cwq->gcwq, cwq);
1726
1727    trace_workqueue_activate_work(work);
1728    move_linked_works(work, pos, NULL);
1729    __clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
1730    cwq->nr_active++;
1731}
1732
1733/**
1734 * cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
1735 * @cwq: cwq of interest
1736 * @color: color of work which left the queue
1737 * @delayed: for a delayed work
1738 *
1739 * A work either has completed or is removed from pending queue,
1740 * decrement nr_in_flight of its cwq and handle workqueue flushing.
1741 *
1742 * CONTEXT:
1743 * spin_lock_irq(gcwq->lock).
1744 */
1745static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
1746                 bool delayed)
1747{
1748    /* ignore uncolored works */
1749    if (color == WORK_NO_COLOR)
1750        return;
1751
1752    cwq->nr_in_flight[color]--;
1753
1754    if (!delayed) {
1755        cwq->nr_active--;
1756        if (!list_empty(&cwq->delayed_works)) {
1757            /* one down, submit a delayed one */
1758            if (cwq->nr_active < cwq->max_active)
1759                cwq_activate_first_delayed(cwq);
1760        }
1761    }
1762
1763    /* is flush in progress and are we at the flushing tip? */
1764    if (likely(cwq->flush_color != color))
1765        return;
1766
1767    /* are there still in-flight works? */
1768    if (cwq->nr_in_flight[color])
1769        return;
1770
1771    /* this cwq is done, clear flush_color */
1772    cwq->flush_color = -1;
1773
1774    /*
1775     * If this was the last cwq, wake up the first flusher. It
1776     * will handle the rest.
1777     */
1778    if (atomic_dec_and_test(&cwq->wq->nr_cwqs_to_flush))
1779        complete(&cwq->wq->first_flusher->done);
1780}
1781
1782/**
1783 * process_one_work - process single work
1784 * @worker: self
1785 * @work: work to process
1786 *
1787 * Process @work. This function contains all the logics necessary to
1788 * process a single work including synchronization against and
1789 * interaction with other workers on the same cpu, queueing and
1790 * flushing. As long as context requirement is met, any worker can
1791 * call this function to process a work.
1792 *
1793 * CONTEXT:
1794 * spin_lock_irq(gcwq->lock) which is released and regrabbed.
1795 */
1796static void process_one_work(struct worker *worker, struct work_struct *work)
1797__releases(&gcwq->lock)
1798__acquires(&gcwq->lock)
1799{
1800    struct cpu_workqueue_struct *cwq = get_work_cwq(work);
1801    struct global_cwq *gcwq = cwq->gcwq;
1802    struct hlist_head *bwh = busy_worker_head(gcwq, work);
1803    bool cpu_intensive = cwq->wq->flags & WQ_CPU_INTENSIVE;
1804    work_func_t f = work->func;
1805    int work_color;
1806    struct worker *collision;
1807#ifdef CONFIG_LOCKDEP
1808    /*
1809     * It is permissible to free the struct work_struct from
1810     * inside the function that is called from it, this we need to
1811     * take into account for lockdep too. To avoid bogus "held
1812     * lock freed" warnings as well as problems when looking into
1813     * work->lockdep_map, make a copy and use that here.
1814     */
1815    struct lockdep_map lockdep_map = work->lockdep_map;
1816#endif
1817    /*
1818     * A single work shouldn't be executed concurrently by
1819     * multiple workers on a single cpu. Check whether anyone is
1820     * already processing the work. If so, defer the work to the
1821     * currently executing one.
1822     */
1823    collision = __find_worker_executing_work(gcwq, bwh, work);
1824    if (unlikely(collision)) {
1825        move_linked_works(work, &collision->scheduled, NULL);
1826        return;
1827    }
1828
1829    /* claim and process */
1830    debug_work_deactivate(work);
1831    hlist_add_head(&worker->hentry, bwh);
1832    worker->current_work = work;
1833    worker->current_cwq = cwq;
1834    work_color = get_work_color(work);
1835
1836    /* record the current cpu number in the work data and dequeue */
1837    set_work_cpu(work, gcwq->cpu);
1838    list_del_init(&work->entry);
1839
1840    /*
1841     * If HIGHPRI_PENDING, check the next work, and, if HIGHPRI,
1842     * wake up another worker; otherwise, clear HIGHPRI_PENDING.
1843     */
1844    if (unlikely(gcwq->flags & GCWQ_HIGHPRI_PENDING)) {
1845        struct work_struct *nwork = list_first_entry(&gcwq->worklist,
1846                        struct work_struct, entry);
1847
1848        if (!list_empty(&gcwq->worklist) &&
1849            get_work_cwq(nwork)->wq->flags & WQ_HIGHPRI)
1850            wake_up_worker(gcwq);
1851        else
1852            gcwq->flags &= ~GCWQ_HIGHPRI_PENDING;
1853    }
1854
1855    /*
1856     * CPU intensive works don't participate in concurrency
1857     * management. They're the scheduler's responsibility.
1858     */
1859    if (unlikely(cpu_intensive))
1860        worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);
1861
1862    spin_unlock_irq(&gcwq->lock);
1863
1864    work_clear_pending(work);
1865    lock_map_acquire_read(&cwq->wq->lockdep_map);
1866    lock_map_acquire(&lockdep_map);
1867    trace_workqueue_execute_start(work);
1868    f(work);
1869    /*
1870     * While we must be careful to not use "work" after this, the trace
1871     * point will only record its address.
1872     */
1873    trace_workqueue_execute_end(work);
1874    lock_map_release(&lockdep_map);
1875    lock_map_release(&cwq->wq->lockdep_map);
1876
1877    if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
1878        printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
1879               "%s/0x%08x/%d\n",
1880               current->comm, preempt_count(), task_pid_nr(current));
1881        printk(KERN_ERR " last function: ");
1882        print_symbol("%s\n", (unsigned long)f);
1883        debug_show_held_locks(current);
1884        dump_stack();
1885    }
1886
1887    spin_lock_irq(&gcwq->lock);
1888
1889    /* clear cpu intensive status */
1890    if (unlikely(cpu_intensive))
1891        worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
1892
1893    /* we're done with it, release */
1894    hlist_del_init(&worker->hentry);
1895    worker->current_work = NULL;
1896    worker->current_cwq = NULL;
1897    cwq_dec_nr_in_flight(cwq, work_color, false);
1898}
1899
1900/**
1901 * process_scheduled_works - process scheduled works
1902 * @worker: self
1903 *
1904 * Process all scheduled works. Please note that the scheduled list
1905 * may change while processing a work, so this function repeatedly
1906 * fetches a work from the top and executes it.
1907 *
1908 * CONTEXT:
1909 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
1910 * multiple times.
1911 */
1912static void process_scheduled_works(struct worker *worker)
1913{
1914    while (!list_empty(&worker->scheduled)) {
1915        struct work_struct *work = list_first_entry(&worker->scheduled,
1916                        struct work_struct, entry);
1917        process_one_work(worker, work);
1918    }
1919}
1920
1921/**
1922 * worker_thread - the worker thread function
1923 * @__worker: self
1924 *
1925 * The gcwq worker thread function. There's a single dynamic pool of
1926 * these per each cpu. These workers process all works regardless of
1927 * their specific target workqueue. The only exception is works which
1928 * belong to workqueues with a rescuer which will be explained in
1929 * rescuer_thread().
1930 */
1931static int worker_thread(void *__worker)
1932{
1933    struct worker *worker = __worker;
1934    struct global_cwq *gcwq = worker->gcwq;
1935
1936    /* tell the scheduler that this is a workqueue worker */
1937    worker->task->flags |= PF_WQ_WORKER;
1938woke_up:
1939    spin_lock_irq(&gcwq->lock);
1940
1941    /* DIE can be set only while we're idle, checking here is enough */
1942    if (worker->flags & WORKER_DIE) {
1943        spin_unlock_irq(&gcwq->lock);
1944        worker->task->flags &= ~PF_WQ_WORKER;
1945        return 0;
1946    }
1947
1948    worker_leave_idle(worker);
1949recheck:
1950    /* no more worker necessary? */
1951    if (!need_more_worker(gcwq))
1952        goto sleep;
1953
1954    /* do we need to manage? */
1955    if (unlikely(!may_start_working(gcwq)) && manage_workers(worker))
1956        goto recheck;
1957
1958    /*
1959     * ->scheduled list can only be filled while a worker is
1960     * preparing to process a work or actually processing it.
1961     * Make sure nobody diddled with it while I was sleeping.
1962     */
1963    BUG_ON(!list_empty(&worker->scheduled));
1964
1965    /*
1966     * When control reaches this point, we're guaranteed to have
1967     * at least one idle worker or that someone else has already
1968     * assumed the manager role.
1969     */
1970    worker_clr_flags(worker, WORKER_PREP);
1971
1972    do {
1973        struct work_struct *work =
1974            list_first_entry(&gcwq->worklist,
1975                     struct work_struct, entry);
1976
1977        if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
1978            /* optimization path, not strictly necessary */
1979            process_one_work(worker, work);
1980            if (unlikely(!list_empty(&worker->scheduled)))
1981                process_scheduled_works(worker);
1982        } else {
1983            move_linked_works(work, &worker->scheduled, NULL);
1984            process_scheduled_works(worker);
1985        }
1986    } while (keep_working(gcwq));
1987
1988    worker_set_flags(worker, WORKER_PREP, false);
1989sleep:
1990    if (unlikely(need_to_manage_workers(gcwq)) && manage_workers(worker))
1991        goto recheck;
1992
1993    /*
1994     * gcwq->lock is held and there's no work to process and no
1995     * need to manage, sleep. Workers are woken up only while
1996     * holding gcwq->lock or from local cpu, so setting the
1997     * current state before releasing gcwq->lock is enough to
1998     * prevent losing any event.
1999     */
2000    worker_enter_idle(worker);
2001    __set_current_state(TASK_INTERRUPTIBLE);
2002    spin_unlock_irq(&gcwq->lock);
2003    schedule();
2004    goto woke_up;
2005}
2006
2007/**
2008 * rescuer_thread - the rescuer thread function
2009 * @__wq: the associated workqueue
2010 *
2011 * Workqueue rescuer thread function. There's one rescuer for each
2012 * workqueue which has WQ_RESCUER set.
2013 *
2014 * Regular work processing on a gcwq may block trying to create a new
2015 * worker which uses GFP_KERNEL allocation which has slight chance of
2016 * developing into deadlock if some works currently on the same queue
2017 * need to be processed to satisfy the GFP_KERNEL allocation. This is
2018 * the problem rescuer solves.
2019 *
2020 * When such condition is possible, the gcwq summons rescuers of all
2021 * workqueues which have works queued on the gcwq and let them process
2022 * those works so that forward progress can be guaranteed.
2023 *
2024 * This should happen rarely.
2025 */
2026static int rescuer_thread(void *__wq)
2027{
2028    struct workqueue_struct *wq = __wq;
2029    struct worker *rescuer = wq->rescuer;
2030    struct list_head *scheduled = &rescuer->scheduled;
2031    bool is_unbound = wq->flags & WQ_UNBOUND;
2032    unsigned int cpu;
2033
2034    set_user_nice(current, RESCUER_NICE_LEVEL);
2035repeat:
2036    set_current_state(TASK_INTERRUPTIBLE);
2037
2038    if (kthread_should_stop())
2039        return 0;
2040
2041    /*
2042     * See whether any cpu is asking for help. Unbounded
2043     * workqueues use cpu 0 in mayday_mask for CPU_UNBOUND.
2044     */
2045    for_each_mayday_cpu(cpu, wq->mayday_mask) {
2046        unsigned int tcpu = is_unbound ? WORK_CPU_UNBOUND : cpu;
2047        struct cpu_workqueue_struct *cwq = get_cwq(tcpu, wq);
2048        struct global_cwq *gcwq = cwq->gcwq;
2049        struct work_struct *work, *n;
2050
2051        __set_current_state(TASK_RUNNING);
2052        mayday_clear_cpu(cpu, wq->mayday_mask);
2053
2054        /* migrate to the target cpu if possible */
2055        rescuer->gcwq = gcwq;
2056        worker_maybe_bind_and_lock(rescuer);
2057
2058        /*
2059         * Slurp in all works issued via this workqueue and
2060         * process'em.
2061         */
2062        BUG_ON(!list_empty(&rescuer->scheduled));
2063        list_for_each_entry_safe(work, n, &gcwq->worklist, entry)
2064            if (get_work_cwq(work) == cwq)
2065                move_linked_works(work, scheduled, &n);
2066
2067        process_scheduled_works(rescuer);
2068
2069        /*
2070         * Leave this gcwq. If keep_working() is %true, notify a
2071         * regular worker; otherwise, we end up with 0 concurrency
2072         * and stalling the execution.
2073         */
2074        if (keep_working(gcwq))
2075            wake_up_worker(gcwq);
2076
2077        spin_unlock_irq(&gcwq->lock);
2078    }
2079
2080    schedule();
2081    goto repeat;
2082}
2083
2084struct wq_barrier {
2085    struct work_struct work;
2086    struct completion done;
2087};
2088
2089static void wq_barrier_func(struct work_struct *work)
2090{
2091    struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
2092    complete(&barr->done);
2093}
2094
2095/**
2096 * insert_wq_barrier - insert a barrier work
2097 * @cwq: cwq to insert barrier into
2098 * @barr: wq_barrier to insert
2099 * @target: target work to attach @barr to
2100 * @worker: worker currently executing @target, NULL if @target is not executing
2101 *
2102 * @barr is linked to @target such that @barr is completed only after
2103 * @target finishes execution. Please note that the ordering
2104 * guarantee is observed only with respect to @target and on the local
2105 * cpu.
2106 *
2107 * Currently, a queued barrier can't be canceled. This is because
2108 * try_to_grab_pending() can't determine whether the work to be
2109 * grabbed is at the head of the queue and thus can't clear LINKED
2110 * flag of the previous work while there must be a valid next work
2111 * after a work with LINKED flag set.
2112 *
2113 * Note that when @worker is non-NULL, @target may be modified
2114 * underneath us, so we can't reliably determine cwq from @target.
2115 *
2116 * CONTEXT:
2117 * spin_lock_irq(gcwq->lock).
2118 */
2119static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
2120                  struct wq_barrier *barr,
2121                  struct work_struct *target, struct worker *worker)
2122{
2123    struct list_head *head;
2124    unsigned int linked = 0;
2125
2126    /*
2127     * debugobject calls are safe here even with gcwq->lock locked
2128     * as we know for sure that this will not trigger any of the
2129     * checks and call back into the fixup functions where we
2130     * might deadlock.
2131     */
2132    INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
2133    __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
2134    init_completion(&barr->done);
2135
2136    /*
2137     * If @target is currently being executed, schedule the
2138     * barrier to the worker; otherwise, put it after @target.
2139     */
2140    if (worker)
2141        head = worker->scheduled.next;
2142    else {
2143        unsigned long *bits = work_data_bits(target);
2144
2145        head = target->entry.next;
2146        /* there can already be other linked works, inherit and set */
2147        linked = *bits & WORK_STRUCT_LINKED;
2148        __set_bit(WORK_STRUCT_LINKED_BIT, bits);
2149    }
2150
2151    debug_work_activate(&barr->work);
2152    insert_work(cwq, &barr->work, head,
2153            work_color_to_flags(WORK_NO_COLOR) | linked);
2154}
2155
2156/**
2157 * flush_workqueue_prep_cwqs - prepare cwqs for workqueue flushing
2158 * @wq: workqueue being flushed
2159 * @flush_color: new flush color, < 0 for no-op
2160 * @work_color: new work color, < 0 for no-op
2161 *
2162 * Prepare cwqs for workqueue flushing.
2163 *
2164 * If @flush_color is non-negative, flush_color on all cwqs should be
2165 * -1. If no cwq has in-flight commands at the specified color, all
2166 * cwq->flush_color's stay at -1 and %false is returned. If any cwq
2167 * has in flight commands, its cwq->flush_color is set to
2168 * @flush_color, @wq->nr_cwqs_to_flush is updated accordingly, cwq
2169 * wakeup logic is armed and %true is returned.
2170 *
2171 * The caller should have initialized @wq->first_flusher prior to
2172 * calling this function with non-negative @flush_color. If
2173 * @flush_color is negative, no flush color update is done and %false
2174 * is returned.
2175 *
2176 * If @work_color is non-negative, all cwqs should have the same
2177 * work_color which is previous to @work_color and all will be
2178 * advanced to @work_color.
2179 *
2180 * CONTEXT:
2181 * mutex_lock(wq->flush_mutex).
2182 *
2183 * RETURNS:
2184 * %true if @flush_color >= 0 and there's something to flush. %false
2185 * otherwise.
2186 */
2187static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,
2188                      int flush_color, int work_color)
2189{
2190    bool wait = false;
2191    unsigned int cpu;
2192
2193    if (flush_color >= 0) {
2194        BUG_ON(atomic_read(&wq->nr_cwqs_to_flush));
2195        atomic_set(&wq->nr_cwqs_to_flush, 1);
2196    }
2197
2198    for_each_cwq_cpu(cpu, wq) {
2199        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
2200        struct global_cwq *gcwq = cwq->gcwq;
2201
2202        spin_lock_irq(&gcwq->lock);
2203
2204        if (flush_color >= 0) {
2205            BUG_ON(cwq->flush_color != -1);
2206
2207            if (cwq->nr_in_flight[flush_color]) {
2208                cwq->flush_color = flush_color;
2209                atomic_inc(&wq->nr_cwqs_to_flush);
2210                wait = true;
2211            }
2212        }
2213
2214        if (work_color >= 0) {
2215            BUG_ON(work_color != work_next_color(cwq->work_color));
2216            cwq->work_color = work_color;
2217        }
2218
2219        spin_unlock_irq(&gcwq->lock);
2220    }
2221
2222    if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_cwqs_to_flush))
2223        complete(&wq->first_flusher->done);
2224
2225    return wait;
2226}
2227
2228/**
2229 * flush_workqueue - ensure that any scheduled work has run to completion.
2230 * @wq: workqueue to flush
2231 *
2232 * Forces execution of the workqueue and blocks until its completion.
2233 * This is typically used in driver shutdown handlers.
2234 *
2235 * We sleep until all works which were queued on entry have been handled,
2236 * but we are not livelocked by new incoming ones.
2237 */
2238void flush_workqueue(struct workqueue_struct *wq)
2239{
2240    struct wq_flusher this_flusher = {
2241        .list = LIST_HEAD_INIT(this_flusher.list),
2242        .flush_color = -1,
2243        .done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
2244    };
2245    int next_color;
2246
2247    lock_map_acquire(&wq->lockdep_map);
2248    lock_map_release(&wq->lockdep_map);
2249
2250    mutex_lock(&wq->flush_mutex);
2251
2252    /*
2253     * Start-to-wait phase
2254     */
2255    next_color = work_next_color(wq->work_color);
2256
2257    if (next_color != wq->flush_color) {
2258        /*
2259         * Color space is not full. The current work_color
2260         * becomes our flush_color and work_color is advanced
2261         * by one.
2262         */
2263        BUG_ON(!list_empty(&wq->flusher_overflow));
2264        this_flusher.flush_color = wq->work_color;
2265        wq->work_color = next_color;
2266
2267        if (!wq->first_flusher) {
2268            /* no flush in progress, become the first flusher */
2269            BUG_ON(wq->flush_color != this_flusher.flush_color);
2270
2271            wq->first_flusher = &this_flusher;
2272
2273            if (!flush_workqueue_prep_cwqs(wq, wq->flush_color,
2274                               wq->work_color)) {
2275                /* nothing to flush, done */
2276                wq->flush_color = next_color;
2277                wq->first_flusher = NULL;
2278                goto out_unlock;
2279            }
2280        } else {
2281            /* wait in queue */
2282            BUG_ON(wq->flush_color == this_flusher.flush_color);
2283            list_add_tail(&this_flusher.list, &wq->flusher_queue);
2284            flush_workqueue_prep_cwqs(wq, -1, wq->work_color);
2285        }
2286    } else {
2287        /*
2288         * Oops, color space is full, wait on overflow queue.
2289         * The next flush completion will assign us
2290         * flush_color and transfer to flusher_queue.
2291         */
2292        list_add_tail(&this_flusher.list, &wq->flusher_overflow);
2293    }
2294
2295    mutex_unlock(&wq->flush_mutex);
2296
2297    wait_for_completion(&this_flusher.done);
2298
2299    /*
2300     * Wake-up-and-cascade phase
2301     *
2302     * First flushers are responsible for cascading flushes and
2303     * handling overflow. Non-first flushers can simply return.
2304     */
2305    if (wq->first_flusher != &this_flusher)
2306        return;
2307
2308    mutex_lock(&wq->flush_mutex);
2309
2310    /* we might have raced, check again with mutex held */
2311    if (wq->first_flusher != &this_flusher)
2312        goto out_unlock;
2313
2314    wq->first_flusher = NULL;
2315
2316    BUG_ON(!list_empty(&this_flusher.list));
2317    BUG_ON(wq->flush_color != this_flusher.flush_color);
2318
2319    while (true) {
2320        struct wq_flusher *next, *tmp;
2321
2322        /* complete all the flushers sharing the current flush color */
2323        list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
2324            if (next->flush_color != wq->flush_color)
2325                break;
2326            list_del_init(&next->list);
2327            complete(&next->done);
2328        }
2329
2330        BUG_ON(!list_empty(&wq->flusher_overflow) &&
2331               wq->flush_color != work_next_color(wq->work_color));
2332
2333        /* this flush_color is finished, advance by one */
2334        wq->flush_color = work_next_color(wq->flush_color);
2335
2336        /* one color has been freed, handle overflow queue */
2337        if (!list_empty(&wq->flusher_overflow)) {
2338            /*
2339             * Assign the same color to all overflowed
2340             * flushers, advance work_color and append to
2341             * flusher_queue. This is the start-to-wait
2342             * phase for these overflowed flushers.
2343             */
2344            list_for_each_entry(tmp, &wq->flusher_overflow, list)
2345                tmp->flush_color = wq->work_color;
2346
2347            wq->work_color = work_next_color(wq->work_color);
2348
2349            list_splice_tail_init(&wq->flusher_overflow,
2350                          &wq->flusher_queue);
2351            flush_workqueue_prep_cwqs(wq, -1, wq->work_color);
2352        }
2353
2354        if (list_empty(&wq->flusher_queue)) {
2355            BUG_ON(wq->flush_color != wq->work_color);
2356            break;
2357        }
2358
2359        /*
2360         * Need to flush more colors. Make the next flusher
2361         * the new first flusher and arm cwqs.
2362         */
2363        BUG_ON(wq->flush_color == wq->work_color);
2364        BUG_ON(wq->flush_color != next->flush_color);
2365
2366        list_del_init(&next->list);
2367        wq->first_flusher = next;
2368
2369        if (flush_workqueue_prep_cwqs(wq, wq->flush_color, -1))
2370            break;
2371
2372        /*
2373         * Meh... this color is already done, clear first
2374         * flusher and repeat cascading.
2375         */
2376        wq->first_flusher = NULL;
2377    }
2378
2379out_unlock:
2380    mutex_unlock(&wq->flush_mutex);
2381}
2382EXPORT_SYMBOL_GPL(flush_workqueue);
2383
2384static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
2385                 bool wait_executing)
2386{
2387    struct worker *worker = NULL;
2388    struct global_cwq *gcwq;
2389    struct cpu_workqueue_struct *cwq;
2390
2391    might_sleep();
2392    gcwq = get_work_gcwq(work);
2393    if (!gcwq)
2394        return false;
2395
2396    spin_lock_irq(&gcwq->lock);
2397    if (!list_empty(&work->entry)) {
2398        /*
2399         * See the comment near try_to_grab_pending()->smp_rmb().
2400         * If it was re-queued to a different gcwq under us, we
2401         * are not going to wait.
2402         */
2403        smp_rmb();
2404        cwq = get_work_cwq(work);
2405        if (unlikely(!cwq || gcwq != cwq->gcwq))
2406            goto already_gone;
2407    } else if (wait_executing) {
2408        worker = find_worker_executing_work(gcwq, work);
2409        if (!worker)
2410            goto already_gone;
2411        cwq = worker->current_cwq;
2412    } else
2413        goto already_gone;
2414
2415    insert_wq_barrier(cwq, barr, work, worker);
2416    spin_unlock_irq(&gcwq->lock);
2417
2418    /*
2419     * If @max_active is 1 or rescuer is in use, flushing another work
2420     * item on the same workqueue may lead to deadlock. Make sure the
2421     * flusher is not running on the same workqueue by verifying write
2422     * access.
2423     */
2424    if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
2425        lock_map_acquire(&cwq->wq->lockdep_map);
2426    else
2427        lock_map_acquire_read(&cwq->wq->lockdep_map);
2428    lock_map_release(&cwq->wq->lockdep_map);
2429
2430    return true;
2431already_gone:
2432    spin_unlock_irq(&gcwq->lock);
2433    return false;
2434}
2435
2436/**
2437 * flush_work - wait for a work to finish executing the last queueing instance
2438 * @work: the work to flush
2439 *
2440 * Wait until @work has finished execution. This function considers
2441 * only the last queueing instance of @work. If @work has been
2442 * enqueued across different CPUs on a non-reentrant workqueue or on
2443 * multiple workqueues, @work might still be executing on return on
2444 * some of the CPUs from earlier queueing.
2445 *
2446 * If @work was queued only on a non-reentrant, ordered or unbound
2447 * workqueue, @work is guaranteed to be idle on return if it hasn't
2448 * been requeued since flush started.
2449 *
2450 * RETURNS:
2451 * %true if flush_work() waited for the work to finish execution,
2452 * %false if it was already idle.
2453 */
2454bool flush_work(struct work_struct *work)
2455{
2456    struct wq_barrier barr;
2457
2458    if (start_flush_work(work, &barr, true)) {
2459        wait_for_completion(&barr.done);
2460        destroy_work_on_stack(&barr.work);
2461        return true;
2462    } else
2463        return false;
2464}
2465EXPORT_SYMBOL_GPL(flush_work);
2466
2467static bool wait_on_cpu_work(struct global_cwq *gcwq, struct work_struct *work)
2468{
2469    struct wq_barrier barr;
2470    struct worker *worker;
2471
2472    spin_lock_irq(&gcwq->lock);
2473
2474    worker = find_worker_executing_work(gcwq, work);
2475    if (unlikely(worker))
2476        insert_wq_barrier(worker->current_cwq, &barr, work, worker);
2477
2478    spin_unlock_irq(&gcwq->lock);
2479
2480    if (unlikely(worker)) {
2481        wait_for_completion(&barr.done);
2482        destroy_work_on_stack(&barr.work);
2483        return true;
2484    } else
2485        return false;
2486}
2487
2488static bool wait_on_work(struct work_struct *work)
2489{
2490    bool ret = false;
2491    int cpu;
2492
2493    might_sleep();
2494
2495    lock_map_acquire(&work->lockdep_map);
2496    lock_map_release(&work->lockdep_map);
2497
2498    for_each_gcwq_cpu(cpu)
2499        ret |= wait_on_cpu_work(get_gcwq(cpu), work);
2500    return ret;
2501}
2502
2503/**
2504 * flush_work_sync - wait until a work has finished execution
2505 * @work: the work to flush
2506 *
2507 * Wait until @work has finished execution. On return, it's
2508 * guaranteed that all queueing instances of @work which happened
2509 * before this function is called are finished. In other words, if
2510 * @work hasn't been requeued since this function was called, @work is
2511 * guaranteed to be idle on return.
2512 *
2513 * RETURNS:
2514 * %true if flush_work_sync() waited for the work to finish execution,
2515 * %false if it was already idle.
2516 */
2517bool flush_work_sync(struct work_struct *work)
2518{
2519    struct wq_barrier barr;
2520    bool pending, waited;
2521
2522    /* we'll wait for executions separately, queue barr only if pending */
2523    pending = start_flush_work(work, &barr, false);
2524
2525    /* wait for executions to finish */
2526    waited = wait_on_work(work);
2527
2528    /* wait for the pending one */
2529    if (pending) {
2530        wait_for_completion(&barr.done);
2531        destroy_work_on_stack(&barr.work);
2532    }
2533
2534    return pending || waited;
2535}
2536EXPORT_SYMBOL_GPL(flush_work_sync);
2537
2538/*
2539 * Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
2540 * so this work can't be re-armed in any way.
2541 */
2542static int try_to_grab_pending(struct work_struct *work)
2543{
2544    struct global_cwq *gcwq;
2545    int ret = -1;
2546
2547    if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
2548        return 0;
2549
2550    /*
2551     * The queueing is in progress, or it is already queued. Try to
2552     * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
2553     */
2554    gcwq = get_work_gcwq(work);
2555    if (!gcwq)
2556        return ret;
2557
2558    spin_lock_irq(&gcwq->lock);
2559    if (!list_empty(&work->entry)) {
2560        /*
2561         * This work is queued, but perhaps we locked the wrong gcwq.
2562         * In that case we must see the new value after rmb(), see
2563         * insert_work()->wmb().
2564         */
2565        smp_rmb();
2566        if (gcwq == get_work_gcwq(work)) {
2567            debug_work_deactivate(work);
2568            list_del_init(&work->entry);
2569            cwq_dec_nr_in_flight(get_work_cwq(work),
2570                get_work_color(work),
2571                *work_data_bits(work) & WORK_STRUCT_DELAYED);
2572            ret = 1;
2573        }
2574    }
2575    spin_unlock_irq(&gcwq->lock);
2576
2577    return ret;
2578}
2579
2580static bool __cancel_work_timer(struct work_struct *work,
2581                struct timer_list* timer)
2582{
2583    int ret;
2584
2585    do {
2586        ret = (timer && likely(del_timer(timer)));
2587        if (!ret)
2588            ret = try_to_grab_pending(work);
2589        wait_on_work(work);
2590    } while (unlikely(ret < 0));
2591
2592    clear_work_data(work);
2593    return ret;
2594}
2595
2596/**
2597 * cancel_work_sync - cancel a work and wait for it to finish
2598 * @work: the work to cancel
2599 *
2600 * Cancel @work and wait for its execution to finish. This function
2601 * can be used even if the work re-queues itself or migrates to
2602 * another workqueue. On return from this function, @work is
2603 * guaranteed to be not pending or executing on any CPU.
2604 *
2605 * cancel_work_sync(&delayed_work->work) must not be used for
2606 * delayed_work's. Use cancel_delayed_work_sync() instead.
2607 *
2608 * The caller must ensure that the workqueue on which @work was last
2609 * queued can't be destroyed before this function returns.
2610 *
2611 * RETURNS:
2612 * %true if @work was pending, %false otherwise.
2613 */
2614bool cancel_work_sync(struct work_struct *work)
2615{
2616    return __cancel_work_timer(work, NULL);
2617}
2618EXPORT_SYMBOL_GPL(cancel_work_sync);
2619
2620/**
2621 * flush_delayed_work - wait for a dwork to finish executing the last queueing
2622 * @dwork: the delayed work to flush
2623 *
2624 * Delayed timer is cancelled and the pending work is queued for
2625 * immediate execution. Like flush_work(), this function only
2626 * considers the last queueing instance of @dwork.
2627 *
2628 * RETURNS:
2629 * %true if flush_work() waited for the work to finish execution,
2630 * %false if it was already idle.
2631 */
2632bool flush_delayed_work(struct delayed_work *dwork)
2633{
2634    if (del_timer_sync(&dwork->timer))
2635        __queue_work(raw_smp_processor_id(),
2636                 get_work_cwq(&dwork->work)->wq, &dwork->work);
2637    return flush_work(&dwork->work);
2638}
2639EXPORT_SYMBOL(flush_delayed_work);
2640
2641/**
2642 * flush_delayed_work_sync - wait for a dwork to finish
2643 * @dwork: the delayed work to flush
2644 *
2645 * Delayed timer is cancelled and the pending work is queued for
2646 * execution immediately. Other than timer handling, its behavior
2647 * is identical to flush_work_sync().
2648 *
2649 * RETURNS:
2650 * %true if flush_work_sync() waited for the work to finish execution,
2651 * %false if it was already idle.
2652 */
2653bool flush_delayed_work_sync(struct delayed_work *dwork)
2654{
2655    if (del_timer_sync(&dwork->timer))
2656        __queue_work(raw_smp_processor_id(),
2657                 get_work_cwq(&dwork->work)->wq, &dwork->work);
2658    return flush_work_sync(&dwork->work);
2659}
2660EXPORT_SYMBOL(flush_delayed_work_sync);
2661
2662/**
2663 * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
2664 * @dwork: the delayed work cancel
2665 *
2666 * This is cancel_work_sync() for delayed works.
2667 *
2668 * RETURNS:
2669 * %true if @dwork was pending, %false otherwise.
2670 */
2671bool cancel_delayed_work_sync(struct delayed_work *dwork)
2672{
2673    return __cancel_work_timer(&dwork->work, &dwork->timer);
2674}
2675EXPORT_SYMBOL(cancel_delayed_work_sync);
2676
2677/**
2678 * schedule_work - put work task in global workqueue
2679 * @work: job to be done
2680 *
2681 * Returns zero if @work was already on the kernel-global workqueue and
2682 * non-zero otherwise.
2683 *
2684 * This puts a job in the kernel-global workqueue if it was not already
2685 * queued and leaves it in the same position on the kernel-global
2686 * workqueue otherwise.
2687 */
2688int schedule_work(struct work_struct *work)
2689{
2690    return queue_work(system_wq, work);
2691}
2692EXPORT_SYMBOL(schedule_work);
2693
2694/*
2695 * schedule_work_on - put work task on a specific cpu
2696 * @cpu: cpu to put the work task on
2697 * @work: job to be done
2698 *
2699 * This puts a job on a specific cpu
2700 */
2701int schedule_work_on(int cpu, struct work_struct *work)
2702{
2703    return queue_work_on(cpu, system_wq, work);
2704}
2705EXPORT_SYMBOL(schedule_work_on);
2706
2707/**
2708 * schedule_delayed_work - put work task in global workqueue after delay
2709 * @dwork: job to be done
2710 * @delay: number of jiffies to wait or 0 for immediate execution
2711 *
2712 * After waiting for a given time this puts a job in the kernel-global
2713 * workqueue.
2714 */
2715int schedule_delayed_work(struct delayed_work *dwork,
2716                    unsigned long delay)
2717{
2718    return queue_delayed_work(system_wq, dwork, delay);
2719}
2720EXPORT_SYMBOL(schedule_delayed_work);
2721
2722/**
2723 * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
2724 * @cpu: cpu to use
2725 * @dwork: job to be done
2726 * @delay: number of jiffies to wait
2727 *
2728 * After waiting for a given time this puts a job in the kernel-global
2729 * workqueue on the specified CPU.
2730 */
2731int schedule_delayed_work_on(int cpu,
2732            struct delayed_work *dwork, unsigned long delay)
2733{
2734    return queue_delayed_work_on(cpu, system_wq, dwork, delay);
2735}
2736EXPORT_SYMBOL(schedule_delayed_work_on);
2737
2738/**
2739 * schedule_on_each_cpu - execute a function synchronously on each online CPU
2740 * @func: the function to call
2741 *
2742 * schedule_on_each_cpu() executes @func on each online CPU using the
2743 * system workqueue and blocks until all CPUs have completed.
2744 * schedule_on_each_cpu() is very slow.
2745 *
2746 * RETURNS:
2747 * 0 on success, -errno on failure.
2748 */
2749int schedule_on_each_cpu(work_func_t func)
2750{
2751    int cpu;
2752    struct work_struct __percpu *works;
2753
2754    works = alloc_percpu(struct work_struct);
2755    if (!works)
2756        return -ENOMEM;
2757
2758    get_online_cpus();
2759
2760    for_each_online_cpu(cpu) {
2761        struct work_struct *work = per_cpu_ptr(works, cpu);
2762
2763        INIT_WORK(work, func);
2764        schedule_work_on(cpu, work);
2765    }
2766
2767    for_each_online_cpu(cpu)
2768        flush_work(per_cpu_ptr(works, cpu));
2769
2770    put_online_cpus();
2771    free_percpu(works);
2772    return 0;
2773}
2774
2775/**
2776 * flush_scheduled_work - ensure that any scheduled work has run to completion.
2777 *
2778 * Forces execution of the kernel-global workqueue and blocks until its
2779 * completion.
2780 *
2781 * Think twice before calling this function! It's very easy to get into
2782 * trouble if you don't take great care. Either of the following situations
2783 * will lead to deadlock:
2784 *
2785 * One of the work items currently on the workqueue needs to acquire
2786 * a lock held by your code or its caller.
2787 *
2788 * Your code is running in the context of a work routine.
2789 *
2790 * They will be detected by lockdep when they occur, but the first might not
2791 * occur very often. It depends on what work items are on the workqueue and
2792 * what locks they need, which you have no control over.
2793 *
2794 * In most situations flushing the entire workqueue is overkill; you merely
2795 * need to know that a particular work item isn't queued and isn't running.
2796 * In such cases you should use cancel_delayed_work_sync() or
2797 * cancel_work_sync() instead.
2798 */
2799void flush_scheduled_work(void)
2800{
2801    flush_workqueue(system_wq);
2802}
2803EXPORT_SYMBOL(flush_scheduled_work);
2804
2805/**
2806 * execute_in_process_context - reliably execute the routine with user context
2807 * @fn: the function to execute
2808 * @ew: guaranteed storage for the execute work structure (must
2809 * be available when the work executes)
2810 *
2811 * Executes the function immediately if process context is available,
2812 * otherwise schedules the function for delayed execution.
2813 *
2814 * Returns: 0 - function was executed
2815 * 1 - function was scheduled for execution
2816 */
2817int execute_in_process_context(work_func_t fn, struct execute_work *ew)
2818{
2819    if (!in_interrupt()) {
2820        fn(&ew->work);
2821        return 0;
2822    }
2823
2824    INIT_WORK(&ew->work, fn);
2825    schedule_work(&ew->work);
2826
2827    return 1;
2828}
2829EXPORT_SYMBOL_GPL(execute_in_process_context);
2830
2831int keventd_up(void)
2832{
2833    return system_wq != NULL;
2834}
2835
2836static int alloc_cwqs(struct workqueue_struct *wq)
2837{
2838    /*
2839     * cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
2840     * Make sure that the alignment isn't lower than that of
2841     * unsigned long long.
2842     */
2843    const size_t size = sizeof(struct cpu_workqueue_struct);
2844    const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
2845                   __alignof__(unsigned long long));
2846#ifdef CONFIG_SMP
2847    bool percpu = !(wq->flags & WQ_UNBOUND);
2848#else
2849    bool percpu = false;
2850#endif
2851
2852    if (percpu)
2853        wq->cpu_wq.pcpu = __alloc_percpu(size, align);
2854    else {
2855        void *ptr;
2856
2857        /*
2858         * Allocate enough room to align cwq and put an extra
2859         * pointer at the end pointing back to the originally
2860         * allocated pointer which will be used for free.
2861         */
2862        ptr = kzalloc(size + align + sizeof(void *), GFP_KERNEL);
2863        if (ptr) {
2864            wq->cpu_wq.single = PTR_ALIGN(ptr, align);
2865            *(void **)(wq->cpu_wq.single + 1) = ptr;
2866        }
2867    }
2868
2869    /* just in case, make sure it's actually aligned */
2870    BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
2871    return wq->cpu_wq.v ? 0 : -ENOMEM;
2872}
2873
2874static void free_cwqs(struct workqueue_struct *wq)
2875{
2876#ifdef CONFIG_SMP
2877    bool percpu = !(wq->flags & WQ_UNBOUND);
2878#else
2879    bool percpu = false;
2880#endif
2881
2882    if (percpu)
2883        free_percpu(wq->cpu_wq.pcpu);
2884    else if (wq->cpu_wq.single) {
2885        /* the pointer to free is stored right after the cwq */
2886        kfree(*(void **)(wq->cpu_wq.single + 1));
2887    }
2888}
2889
2890static int wq_clamp_max_active(int max_active, unsigned int flags,
2891                   const char *name)
2892{
2893    int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
2894
2895    if (max_active < 1 || max_active > lim)
2896        printk(KERN_WARNING "workqueue: max_active %d requested for %s "
2897               "is out of range, clamping between %d and %d\n",
2898               max_active, name, 1, lim);
2899
2900    return clamp_val(max_active, 1, lim);
2901}
2902
2903struct workqueue_struct *__alloc_workqueue_key(const char *name,
2904                           unsigned int flags,
2905                           int max_active,
2906                           struct lock_class_key *key,
2907                           const char *lock_name)
2908{
2909    struct workqueue_struct *wq;
2910    unsigned int cpu;
2911
2912    /*
2913     * Workqueues which may be used during memory reclaim should
2914     * have a rescuer to guarantee forward progress.
2915     */
2916    if (flags & WQ_MEM_RECLAIM)
2917        flags |= WQ_RESCUER;
2918
2919    /*
2920     * Unbound workqueues aren't concurrency managed and should be
2921     * dispatched to workers immediately.
2922     */
2923    if (flags & WQ_UNBOUND)
2924        flags |= WQ_HIGHPRI;
2925
2926    max_active = max_active ?: WQ_DFL_ACTIVE;
2927    max_active = wq_clamp_max_active(max_active, flags, name);
2928
2929    wq = kzalloc(sizeof(*wq), GFP_KERNEL);
2930    if (!wq)
2931        goto err;
2932
2933    wq->flags = flags;
2934    wq->saved_max_active = max_active;
2935    mutex_init(&wq->flush_mutex);
2936    atomic_set(&wq->nr_cwqs_to_flush, 0);
2937    INIT_LIST_HEAD(&wq->flusher_queue);
2938    INIT_LIST_HEAD(&wq->flusher_overflow);
2939
2940    wq->name = name;
2941    lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
2942    INIT_LIST_HEAD(&wq->list);
2943
2944    if (alloc_cwqs(wq) < 0)
2945        goto err;
2946
2947    for_each_cwq_cpu(cpu, wq) {
2948        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
2949        struct global_cwq *gcwq = get_gcwq(cpu);
2950
2951        BUG_ON((unsigned long)cwq & WORK_STRUCT_FLAG_MASK);
2952        cwq->gcwq = gcwq;
2953        cwq->wq = wq;
2954        cwq->flush_color = -1;
2955        cwq->max_active = max_active;
2956        INIT_LIST_HEAD(&cwq->delayed_works);
2957    }
2958
2959    if (flags & WQ_RESCUER) {
2960        struct worker *rescuer;
2961
2962        if (!alloc_mayday_mask(&wq->mayday_mask, GFP_KERNEL))
2963            goto err;
2964
2965        wq->rescuer = rescuer = alloc_worker();
2966        if (!rescuer)
2967            goto err;
2968
2969        rescuer->task = kthread_create(rescuer_thread, wq, "%s", name);
2970        if (IS_ERR(rescuer->task))
2971            goto err;
2972
2973        rescuer->task->flags |= PF_THREAD_BOUND;
2974        wake_up_process(rescuer->task);
2975    }
2976
2977    /*
2978     * workqueue_lock protects global freeze state and workqueues
2979     * list. Grab it, set max_active accordingly and add the new
2980     * workqueue to workqueues list.
2981     */
2982    spin_lock(&workqueue_lock);
2983
2984    if (workqueue_freezing && wq->flags & WQ_FREEZABLE)
2985        for_each_cwq_cpu(cpu, wq)
2986            get_cwq(cpu, wq)->max_active = 0;
2987
2988    list_add(&wq->list, &workqueues);
2989
2990    spin_unlock(&workqueue_lock);
2991
2992    return wq;
2993err:
2994    if (wq) {
2995        free_cwqs(wq);
2996        free_mayday_mask(wq->mayday_mask);
2997        kfree(wq->rescuer);
2998        kfree(wq);
2999    }
3000    return NULL;
3001}
3002EXPORT_SYMBOL_GPL(__alloc_workqueue_key);
3003
3004/**
3005 * destroy_workqueue - safely terminate a workqueue
3006 * @wq: target workqueue
3007 *
3008 * Safely destroy a workqueue. All work currently pending will be done first.
3009 */
3010void destroy_workqueue(struct workqueue_struct *wq)
3011{
3012    unsigned int flush_cnt = 0;
3013    unsigned int cpu;
3014
3015    /*
3016     * Mark @wq dying and drain all pending works. Once WQ_DYING is
3017     * set, only chain queueing is allowed. IOW, only currently
3018     * pending or running work items on @wq can queue further work
3019     * items on it. @wq is flushed repeatedly until it becomes empty.
3020     * The number of flushing is detemined by the depth of chaining and
3021     * should be relatively short. Whine if it takes too long.
3022     */
3023    wq->flags |= WQ_DYING;
3024reflush:
3025    flush_workqueue(wq);
3026
3027    for_each_cwq_cpu(cpu, wq) {
3028        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
3029
3030        if (!cwq->nr_active && list_empty(&cwq->delayed_works))
3031            continue;
3032
3033        if (++flush_cnt == 10 ||
3034            (flush_cnt % 100 == 0 && flush_cnt <= 1000))
3035            printk(KERN_WARNING "workqueue %s: flush on "
3036                   "destruction isn't complete after %u tries\n",
3037                   wq->name, flush_cnt);
3038        goto reflush;
3039    }
3040
3041    /*
3042     * wq list is used to freeze wq, remove from list after
3043     * flushing is complete in case freeze races us.
3044     */
3045    spin_lock(&workqueue_lock);
3046    list_del(&wq->list);
3047    spin_unlock(&workqueue_lock);
3048
3049    /* sanity check */
3050    for_each_cwq_cpu(cpu, wq) {
3051        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
3052        int i;
3053
3054        for (i = 0; i < WORK_NR_COLORS; i++)
3055            BUG_ON(cwq->nr_in_flight[i]);
3056        BUG_ON(cwq->nr_active);
3057        BUG_ON(!list_empty(&cwq->delayed_works));
3058    }
3059
3060    if (wq->flags & WQ_RESCUER) {
3061        kthread_stop(wq->rescuer->task);
3062        free_mayday_mask(wq->mayday_mask);
3063        kfree(wq->rescuer);
3064    }
3065
3066    free_cwqs(wq);
3067    kfree(wq);
3068}
3069EXPORT_SYMBOL_GPL(destroy_workqueue);
3070
3071/**
3072 * workqueue_set_max_active - adjust max_active of a workqueue
3073 * @wq: target workqueue
3074 * @max_active: new max_active value.
3075 *
3076 * Set max_active of @wq to @max_active.
3077 *
3078 * CONTEXT:
3079 * Don't call from IRQ context.
3080 */
3081void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
3082{
3083    unsigned int cpu;
3084
3085    max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
3086
3087    spin_lock(&workqueue_lock);
3088
3089    wq->saved_max_active = max_active;
3090
3091    for_each_cwq_cpu(cpu, wq) {
3092        struct global_cwq *gcwq = get_gcwq(cpu);
3093
3094        spin_lock_irq(&gcwq->lock);
3095
3096        if (!(wq->flags & WQ_FREEZABLE) ||
3097            !(gcwq->flags & GCWQ_FREEZING))
3098            get_cwq(gcwq->cpu, wq)->max_active = max_active;
3099
3100        spin_unlock_irq(&gcwq->lock);
3101    }
3102
3103    spin_unlock(&workqueue_lock);
3104}
3105EXPORT_SYMBOL_GPL(workqueue_set_max_active);
3106
3107/**
3108 * workqueue_congested - test whether a workqueue is congested
3109 * @cpu: CPU in question
3110 * @wq: target workqueue
3111 *
3112 * Test whether @wq's cpu workqueue for @cpu is congested. There is
3113 * no synchronization around this function and the test result is
3114 * unreliable and only useful as advisory hints or for debugging.
3115 *
3116 * RETURNS:
3117 * %true if congested, %false otherwise.
3118 */
3119bool workqueue_congested(unsigned int cpu, struct workqueue_struct *wq)
3120{
3121    struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
3122
3123    return !list_empty(&cwq->delayed_works);
3124}
3125EXPORT_SYMBOL_GPL(workqueue_congested);
3126
3127/**
3128 * work_cpu - return the last known associated cpu for @work
3129 * @work: the work of interest
3130 *
3131 * RETURNS:
3132 * CPU number if @work was ever queued. WORK_CPU_NONE otherwise.
3133 */
3134unsigned int work_cpu(struct work_struct *work)
3135{
3136    struct global_cwq *gcwq = get_work_gcwq(work);
3137
3138    return gcwq ? gcwq->cpu : WORK_CPU_NONE;
3139}
3140EXPORT_SYMBOL_GPL(work_cpu);
3141
3142/**
3143 * work_busy - test whether a work is currently pending or running
3144 * @work: the work to be tested
3145 *
3146 * Test whether @work is currently pending or running. There is no
3147 * synchronization around this function and the test result is
3148 * unreliable and only useful as advisory hints or for debugging.
3149 * Especially for reentrant wqs, the pending state might hide the
3150 * running state.
3151 *
3152 * RETURNS:
3153 * OR'd bitmask of WORK_BUSY_* bits.
3154 */
3155unsigned int work_busy(struct work_struct *work)
3156{
3157    struct global_cwq *gcwq = get_work_gcwq(work);
3158    unsigned long flags;
3159    unsigned int ret = 0;
3160
3161    if (!gcwq)
3162        return false;
3163
3164    spin_lock_irqsave(&gcwq->lock, flags);
3165
3166    if (work_pending(work))
3167        ret |= WORK_BUSY_PENDING;
3168    if (find_worker_executing_work(gcwq, work))
3169        ret |= WORK_BUSY_RUNNING;
3170
3171    spin_unlock_irqrestore(&gcwq->lock, flags);
3172
3173    return ret;
3174}
3175EXPORT_SYMBOL_GPL(work_busy);
3176
3177/*
3178 * CPU hotplug.
3179 *
3180 * There are two challenges in supporting CPU hotplug. Firstly, there
3181 * are a lot of assumptions on strong associations among work, cwq and
3182 * gcwq which make migrating pending and scheduled works very
3183 * difficult to implement without impacting hot paths. Secondly,
3184 * gcwqs serve mix of short, long and very long running works making
3185 * blocked draining impractical.
3186 *
3187 * This is solved by allowing a gcwq to be detached from CPU, running
3188 * it with unbound (rogue) workers and allowing it to be reattached
3189 * later if the cpu comes back online. A separate thread is created
3190 * to govern a gcwq in such state and is called the trustee of the
3191 * gcwq.
3192 *
3193 * Trustee states and their descriptions.
3194 *
3195 * START Command state used on startup. On CPU_DOWN_PREPARE, a
3196 * new trustee is started with this state.
3197 *
3198 * IN_CHARGE Once started, trustee will enter this state after
3199 * assuming the manager role and making all existing
3200 * workers rogue. DOWN_PREPARE waits for trustee to
3201 * enter this state. After reaching IN_CHARGE, trustee
3202 * tries to execute the pending worklist until it's empty
3203 * and the state is set to BUTCHER, or the state is set
3204 * to RELEASE.
3205 *
3206 * BUTCHER Command state which is set by the cpu callback after
3207 * the cpu has went down. Once this state is set trustee
3208 * knows that there will be no new works on the worklist
3209 * and once the worklist is empty it can proceed to
3210 * killing idle workers.
3211 *
3212 * RELEASE Command state which is set by the cpu callback if the
3213 * cpu down has been canceled or it has come online
3214 * again. After recognizing this state, trustee stops
3215 * trying to drain or butcher and clears ROGUE, rebinds
3216 * all remaining workers back to the cpu and releases
3217 * manager role.
3218 *
3219 * DONE Trustee will enter this state after BUTCHER or RELEASE
3220 * is complete.
3221 *
3222 * trustee CPU draining
3223 * took over down complete
3224 * START -----------> IN_CHARGE -----------> BUTCHER -----------> DONE
3225 * | | ^
3226 * | CPU is back online v return workers |
3227 * ----------------> RELEASE --------------
3228 */
3229
3230/**
3231 * trustee_wait_event_timeout - timed event wait for trustee
3232 * @cond: condition to wait for
3233 * @timeout: timeout in jiffies
3234 *
3235 * wait_event_timeout() for trustee to use. Handles locking and
3236 * checks for RELEASE request.
3237 *
3238 * CONTEXT:
3239 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
3240 * multiple times. To be used by trustee.
3241 *
3242 * RETURNS:
3243 * Positive indicating left time if @cond is satisfied, 0 if timed
3244 * out, -1 if canceled.
3245 */
3246#define trustee_wait_event_timeout(cond, timeout) ({ \
3247    long __ret = (timeout); \
3248    while (!((cond) || (gcwq->trustee_state == TRUSTEE_RELEASE)) && \
3249           __ret) { \
3250        spin_unlock_irq(&gcwq->lock); \
3251        __wait_event_timeout(gcwq->trustee_wait, (cond) || \
3252            (gcwq->trustee_state == TRUSTEE_RELEASE), \
3253            __ret); \
3254        spin_lock_irq(&gcwq->lock); \
3255    } \
3256    gcwq->trustee_state == TRUSTEE_RELEASE ? -1 : (__ret); \
3257})
3258
3259/**
3260 * trustee_wait_event - event wait for trustee
3261 * @cond: condition to wait for
3262 *
3263 * wait_event() for trustee to use. Automatically handles locking and
3264 * checks for CANCEL request.
3265 *
3266 * CONTEXT:
3267 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
3268 * multiple times. To be used by trustee.
3269 *
3270 * RETURNS:
3271 * 0 if @cond is satisfied, -1 if canceled.
3272 */
3273#define trustee_wait_event(cond) ({ \
3274    long __ret1; \
3275    __ret1 = trustee_wait_event_timeout(cond, MAX_SCHEDULE_TIMEOUT);\
3276    __ret1 < 0 ? -1 : 0; \
3277})
3278
3279static int __cpuinit trustee_thread(void *__gcwq)
3280{
3281    struct global_cwq *gcwq = __gcwq;
3282    struct worker *worker;
3283    struct work_struct *work;
3284    struct hlist_node *pos;
3285    long rc;
3286    int i;
3287
3288    BUG_ON(gcwq->cpu != smp_processor_id());
3289
3290    spin_lock_irq(&gcwq->lock);
3291    /*
3292     * Claim the manager position and make all workers rogue.
3293     * Trustee must be bound to the target cpu and can't be
3294     * cancelled.
3295     */
3296    BUG_ON(gcwq->cpu != smp_processor_id());
3297    rc = trustee_wait_event(!(gcwq->flags & GCWQ_MANAGING_WORKERS));
3298    BUG_ON(rc < 0);
3299
3300    gcwq->flags |= GCWQ_MANAGING_WORKERS;
3301
3302    list_for_each_entry(worker, &gcwq->idle_list, entry)
3303        worker->flags |= WORKER_ROGUE;
3304
3305    for_each_busy_worker(worker, i, pos, gcwq)
3306        worker->flags |= WORKER_ROGUE;
3307
3308    /*
3309     * Call schedule() so that we cross rq->lock and thus can
3310     * guarantee sched callbacks see the rogue flag. This is
3311     * necessary as scheduler callbacks may be invoked from other
3312     * cpus.
3313     */
3314    spin_unlock_irq(&gcwq->lock);
3315    schedule();
3316    spin_lock_irq(&gcwq->lock);
3317
3318    /*
3319     * Sched callbacks are disabled now. Zap nr_running. After
3320     * this, nr_running stays zero and need_more_worker() and
3321     * keep_working() are always true as long as the worklist is
3322     * not empty.
3323     */
3324    atomic_set(get_gcwq_nr_running(gcwq->cpu), 0);
3325
3326    spin_unlock_irq(&gcwq->lock);
3327    del_timer_sync(&gcwq->idle_timer);
3328    spin_lock_irq(&gcwq->lock);
3329
3330    /*
3331     * We're now in charge. Notify and proceed to drain. We need
3332     * to keep the gcwq running during the whole CPU down
3333     * procedure as other cpu hotunplug callbacks may need to
3334     * flush currently running tasks.
3335     */
3336    gcwq->trustee_state = TRUSTEE_IN_CHARGE;
3337    wake_up_all(&gcwq->trustee_wait);
3338
3339    /*
3340     * The original cpu is in the process of dying and may go away
3341     * anytime now. When that happens, we and all workers would
3342     * be migrated to other cpus. Try draining any left work. We
3343     * want to get it over with ASAP - spam rescuers, wake up as
3344     * many idlers as necessary and create new ones till the
3345     * worklist is empty. Note that if the gcwq is frozen, there
3346     * may be frozen works in freezable cwqs. Don't declare
3347     * completion while frozen.
3348     */
3349    while (gcwq->nr_workers != gcwq->nr_idle ||
3350           gcwq->flags & GCWQ_FREEZING ||
3351           gcwq->trustee_state == TRUSTEE_IN_CHARGE) {
3352        int nr_works = 0;
3353
3354        list_for_each_entry(work, &gcwq->worklist, entry) {
3355            send_mayday(work);
3356            nr_works++;
3357        }
3358
3359        list_for_each_entry(worker, &gcwq->idle_list, entry) {
3360            if (!nr_works--)
3361                break;
3362            wake_up_process(worker->task);
3363        }
3364
3365        if (need_to_create_worker(gcwq)) {
3366            spin_unlock_irq(&gcwq->lock);
3367            worker = create_worker(gcwq, false);
3368            spin_lock_irq(&gcwq->lock);
3369            if (worker) {
3370                worker->flags |= WORKER_ROGUE;
3371                start_worker(worker);
3372            }
3373        }
3374
3375        /* give a breather */
3376        if (trustee_wait_event_timeout(false, TRUSTEE_COOLDOWN) < 0)
3377            break;
3378    }
3379
3380    /*
3381     * Either all works have been scheduled and cpu is down, or
3382     * cpu down has already been canceled. Wait for and butcher
3383     * all workers till we're canceled.
3384     */
3385    do {
3386        rc = trustee_wait_event(!list_empty(&gcwq->idle_list));
3387        while (!list_empty(&gcwq->idle_list))
3388            destroy_worker(list_first_entry(&gcwq->idle_list,
3389                            struct worker, entry));
3390    } while (gcwq->nr_workers && rc >= 0);
3391
3392    /*
3393     * At this point, either draining has completed and no worker
3394     * is left, or cpu down has been canceled or the cpu is being
3395     * brought back up. There shouldn't be any idle one left.
3396     * Tell the remaining busy ones to rebind once it finishes the
3397     * currently scheduled works by scheduling the rebind_work.
3398     */
3399    WARN_ON(!list_empty(&gcwq->idle_list));
3400
3401    for_each_busy_worker(worker, i, pos, gcwq) {
3402        struct work_struct *rebind_work = &worker->rebind_work;
3403
3404        /*
3405         * Rebind_work may race with future cpu hotplug
3406         * operations. Use a separate flag to mark that
3407         * rebinding is scheduled.
3408         */
3409        worker->flags |= WORKER_REBIND;
3410        worker->flags &= ~WORKER_ROGUE;
3411
3412        /* queue rebind_work, wq doesn't matter, use the default one */
3413        if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
3414                     work_data_bits(rebind_work)))
3415            continue;
3416
3417        debug_work_activate(rebind_work);
3418        insert_work(get_cwq(gcwq->cpu, system_wq), rebind_work,
3419                worker->scheduled.next,
3420                work_color_to_flags(WORK_NO_COLOR));
3421    }
3422
3423    /* relinquish manager role */
3424    gcwq->flags &= ~GCWQ_MANAGING_WORKERS;
3425
3426    /* notify completion */
3427    gcwq->trustee = NULL;
3428    gcwq->trustee_state = TRUSTEE_DONE;
3429    wake_up_all(&gcwq->trustee_wait);
3430    spin_unlock_irq(&gcwq->lock);
3431    return 0;
3432}
3433
3434/**
3435 * wait_trustee_state - wait for trustee to enter the specified state
3436 * @gcwq: gcwq the trustee of interest belongs to
3437 * @state: target state to wait for
3438 *
3439 * Wait for the trustee to reach @state. DONE is already matched.
3440 *
3441 * CONTEXT:
3442 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
3443 * multiple times. To be used by cpu_callback.
3444 */
3445static void __cpuinit wait_trustee_state(struct global_cwq *gcwq, int state)
3446__releases(&gcwq->lock)
3447__acquires(&gcwq->lock)
3448{
3449    if (!(gcwq->trustee_state == state ||
3450          gcwq->trustee_state == TRUSTEE_DONE)) {
3451        spin_unlock_irq(&gcwq->lock);
3452        __wait_event(gcwq->trustee_wait,
3453                 gcwq->trustee_state == state ||
3454                 gcwq->trustee_state == TRUSTEE_DONE);
3455        spin_lock_irq(&gcwq->lock);
3456    }
3457}
3458
3459static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
3460                        unsigned long action,
3461                        void *hcpu)
3462{
3463    unsigned int cpu = (unsigned long)hcpu;
3464    struct global_cwq *gcwq = get_gcwq(cpu);
3465    struct task_struct *new_trustee = NULL;
3466    struct worker *uninitialized_var(new_worker);
3467    unsigned long flags;
3468
3469    action &= ~CPU_TASKS_FROZEN;
3470
3471    switch (action) {
3472    case CPU_DOWN_PREPARE:
3473        new_trustee = kthread_create(trustee_thread, gcwq,
3474                         "workqueue_trustee/%d\n", cpu);
3475        if (IS_ERR(new_trustee))
3476            return notifier_from_errno(PTR_ERR(new_trustee));
3477        kthread_bind(new_trustee, cpu);
3478        /* fall through */
3479    case CPU_UP_PREPARE:
3480        BUG_ON(gcwq->first_idle);
3481        new_worker = create_worker(gcwq, false);
3482        if (!new_worker) {
3483            if (new_trustee)
3484                kthread_stop(new_trustee);
3485            return NOTIFY_BAD;
3486        }
3487    }
3488
3489    /* some are called w/ irq disabled, don't disturb irq status */
3490    spin_lock_irqsave(&gcwq->lock, flags);
3491
3492    switch (action) {
3493    case CPU_DOWN_PREPARE:
3494        /* initialize trustee and tell it to acquire the gcwq */
3495        BUG_ON(gcwq->trustee || gcwq->trustee_state != TRUSTEE_DONE);
3496        gcwq->trustee = new_trustee;
3497        gcwq->trustee_state = TRUSTEE_START;
3498        wake_up_process(gcwq->trustee);
3499        wait_trustee_state(gcwq, TRUSTEE_IN_CHARGE);
3500        /* fall through */
3501    case CPU_UP_PREPARE:
3502        BUG_ON(gcwq->first_idle);
3503        gcwq->first_idle = new_worker;
3504        break;
3505
3506    case CPU_DYING:
3507        /*
3508         * Before this, the trustee and all workers except for
3509         * the ones which are still executing works from
3510         * before the last CPU down must be on the cpu. After
3511         * this, they'll all be diasporas.
3512         */
3513        gcwq->flags |= GCWQ_DISASSOCIATED;
3514        break;
3515
3516    case CPU_POST_DEAD:
3517        gcwq->trustee_state = TRUSTEE_BUTCHER;
3518        /* fall through */
3519    case CPU_UP_CANCELED:
3520        destroy_worker(gcwq->first_idle);
3521        gcwq->first_idle = NULL;
3522        break;
3523
3524    case CPU_DOWN_FAILED:
3525    case CPU_ONLINE:
3526        gcwq->flags &= ~GCWQ_DISASSOCIATED;
3527        if (gcwq->trustee_state != TRUSTEE_DONE) {
3528            gcwq->trustee_state = TRUSTEE_RELEASE;
3529            wake_up_process(gcwq->trustee);
3530            wait_trustee_state(gcwq, TRUSTEE_DONE);
3531        }
3532
3533        /*
3534         * Trustee is done and there might be no worker left.
3535         * Put the first_idle in and request a real manager to
3536         * take a look.
3537         */
3538        spin_unlock_irq(&gcwq->lock);
3539        kthread_bind(gcwq->first_idle->task, cpu);
3540        spin_lock_irq(&gcwq->lock);
3541        gcwq->flags |= GCWQ_MANAGE_WORKERS;
3542        start_worker(gcwq->first_idle);
3543        gcwq->first_idle = NULL;
3544        break;
3545    }
3546
3547    spin_unlock_irqrestore(&gcwq->lock, flags);
3548
3549    return notifier_from_errno(0);
3550}
3551
3552#ifdef CONFIG_SMP
3553
3554struct work_for_cpu {
3555    struct completion completion;
3556    long (*fn)(void *);
3557    void *arg;
3558    long ret;
3559};
3560
3561static int do_work_for_cpu(void *_wfc)
3562{
3563    struct work_for_cpu *wfc = _wfc;
3564    wfc->ret = wfc->fn(wfc->arg);
3565    complete(&wfc->completion);
3566    return 0;
3567}
3568
3569/**
3570 * work_on_cpu - run a function in user context on a particular cpu
3571 * @cpu: the cpu to run on
3572 * @fn: the function to run
3573 * @arg: the function arg
3574 *
3575 * This will return the value @fn returns.
3576 * It is up to the caller to ensure that the cpu doesn't go offline.
3577 * The caller must not hold any locks which would prevent @fn from completing.
3578 */
3579long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
3580{
3581    struct task_struct *sub_thread;
3582    struct work_for_cpu wfc = {
3583        .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
3584        .fn = fn,
3585        .arg = arg,
3586    };
3587
3588    sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
3589    if (IS_ERR(sub_thread))
3590        return PTR_ERR(sub_thread);
3591    kthread_bind(sub_thread, cpu);
3592    wake_up_process(sub_thread);
3593    wait_for_completion(&wfc.completion);
3594    return wfc.ret;
3595}
3596EXPORT_SYMBOL_GPL(work_on_cpu);
3597#endif /* CONFIG_SMP */
3598
3599#ifdef CONFIG_FREEZER
3600
3601/**
3602 * freeze_workqueues_begin - begin freezing workqueues
3603 *
3604 * Start freezing workqueues. After this function returns, all freezable
3605 * workqueues will queue new works to their frozen_works list instead of
3606 * gcwq->worklist.
3607 *
3608 * CONTEXT:
3609 * Grabs and releases workqueue_lock and gcwq->lock's.
3610 */
3611void freeze_workqueues_begin(void)
3612{
3613    unsigned int cpu;
3614
3615    spin_lock(&workqueue_lock);
3616
3617    BUG_ON(workqueue_freezing);
3618    workqueue_freezing = true;
3619
3620    for_each_gcwq_cpu(cpu) {
3621        struct global_cwq *gcwq = get_gcwq(cpu);
3622        struct workqueue_struct *wq;
3623
3624        spin_lock_irq(&gcwq->lock);
3625
3626        BUG_ON(gcwq->flags & GCWQ_FREEZING);
3627        gcwq->flags |= GCWQ_FREEZING;
3628
3629        list_for_each_entry(wq, &workqueues, list) {
3630            struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
3631
3632            if (cwq && wq->flags & WQ_FREEZABLE)
3633                cwq->max_active = 0;
3634        }
3635
3636        spin_unlock_irq(&gcwq->lock);
3637    }
3638
3639    spin_unlock(&workqueue_lock);
3640}
3641
3642/**
3643 * freeze_workqueues_busy - are freezable workqueues still busy?
3644 *
3645 * Check whether freezing is complete. This function must be called
3646 * between freeze_workqueues_begin() and thaw_workqueues().
3647 *
3648 * CONTEXT:
3649 * Grabs and releases workqueue_lock.
3650 *
3651 * RETURNS:
3652 * %true if some freezable workqueues are still busy. %false if freezing
3653 * is complete.
3654 */
3655bool freeze_workqueues_busy(void)
3656{
3657    unsigned int cpu;
3658    bool busy = false;
3659
3660    spin_lock(&workqueue_lock);
3661
3662    BUG_ON(!workqueue_freezing);
3663
3664    for_each_gcwq_cpu(cpu) {
3665        struct workqueue_struct *wq;
3666        /*
3667         * nr_active is monotonically decreasing. It's safe
3668         * to peek without lock.
3669         */
3670        list_for_each_entry(wq, &workqueues, list) {
3671            struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
3672
3673            if (!cwq || !(wq->flags & WQ_FREEZABLE))
3674                continue;
3675
3676            BUG_ON(cwq->nr_active < 0);
3677            if (cwq->nr_active) {
3678                busy = true;
3679                goto out_unlock;
3680            }
3681        }
3682    }
3683out_unlock:
3684    spin_unlock(&workqueue_lock);
3685    return busy;
3686}
3687
3688/**
3689 * thaw_workqueues - thaw workqueues
3690 *
3691 * Thaw workqueues. Normal queueing is restored and all collected
3692 * frozen works are transferred to their respective gcwq worklists.
3693 *
3694 * CONTEXT:
3695 * Grabs and releases workqueue_lock and gcwq->lock's.
3696 */
3697void thaw_workqueues(void)
3698{
3699    unsigned int cpu;
3700
3701    spin_lock(&workqueue_lock);
3702
3703    if (!workqueue_freezing)
3704        goto out_unlock;
3705
3706    for_each_gcwq_cpu(cpu) {
3707        struct global_cwq *gcwq = get_gcwq(cpu);
3708        struct workqueue_struct *wq;
3709
3710        spin_lock_irq(&gcwq->lock);
3711
3712        BUG_ON(!(gcwq->flags & GCWQ_FREEZING));
3713        gcwq->flags &= ~GCWQ_FREEZING;
3714
3715        list_for_each_entry(wq, &workqueues, list) {
3716            struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
3717
3718            if (!cwq || !(wq->flags & WQ_FREEZABLE))
3719                continue;
3720
3721            /* restore max_active and repopulate worklist */
3722            cwq->max_active = wq->saved_max_active;
3723
3724            while (!list_empty(&cwq->delayed_works) &&
3725                   cwq->nr_active < cwq->max_active)
3726                cwq_activate_first_delayed(cwq);
3727        }
3728
3729        wake_up_worker(gcwq);
3730
3731        spin_unlock_irq(&gcwq->lock);
3732    }
3733
3734    workqueue_freezing = false;
3735out_unlock:
3736    spin_unlock(&workqueue_lock);
3737}
3738#endif /* CONFIG_FREEZER */
3739
3740static int __init init_workqueues(void)
3741{
3742    unsigned int cpu;
3743    int i;
3744
3745    cpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);
3746
3747    /* initialize gcwqs */
3748    for_each_gcwq_cpu(cpu) {
3749        struct global_cwq *gcwq = get_gcwq(cpu);
3750
3751        spin_lock_init(&gcwq->lock);
3752        INIT_LIST_HEAD(&gcwq->worklist);
3753        gcwq->cpu = cpu;
3754        gcwq->flags |= GCWQ_DISASSOCIATED;
3755
3756        INIT_LIST_HEAD(&gcwq->idle_list);
3757        for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)
3758            INIT_HLIST_HEAD(&gcwq->busy_hash[i]);
3759
3760        init_timer_deferrable(&gcwq->idle_timer);
3761        gcwq->idle_timer.function = idle_worker_timeout;
3762        gcwq->idle_timer.data = (unsigned long)gcwq;
3763
3764        setup_timer(&gcwq->mayday_timer, gcwq_mayday_timeout,
3765                (unsigned long)gcwq);
3766
3767        ida_init(&gcwq->worker_ida);
3768
3769        gcwq->trustee_state = TRUSTEE_DONE;
3770        init_waitqueue_head(&gcwq->trustee_wait);
3771    }
3772
3773    /* create the initial worker */
3774    for_each_online_gcwq_cpu(cpu) {
3775        struct global_cwq *gcwq = get_gcwq(cpu);
3776        struct worker *worker;
3777
3778        if (cpu != WORK_CPU_UNBOUND)
3779            gcwq->flags &= ~GCWQ_DISASSOCIATED;
3780        worker = create_worker(gcwq, true);
3781        BUG_ON(!worker);
3782        spin_lock_irq(&gcwq->lock);
3783        start_worker(worker);
3784        spin_unlock_irq(&gcwq->lock);
3785    }
3786
3787    system_wq = alloc_workqueue("events", 0, 0);
3788    system_long_wq = alloc_workqueue("events_long", 0, 0);
3789    system_nrt_wq = alloc_workqueue("events_nrt", WQ_NON_REENTRANT, 0);
3790    system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
3791                        WQ_UNBOUND_MAX_ACTIVE);
3792    system_freezable_wq = alloc_workqueue("events_freezable",
3793                          WQ_FREEZABLE, 0);
3794    BUG_ON(!system_wq || !system_long_wq || !system_nrt_wq ||
3795           !system_unbound_wq || !system_freezable_wq);
3796    return 0;
3797}
3798early_initcall(init_workqueues);
3799

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