Root/kernel/rcutree.h

1/*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions.
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 *
19 * Copyright IBM Corporation, 2008
20 *
21 * Author: Ingo Molnar <mingo@elte.hu>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
23 */
24
25#include <linux/cache.h>
26#include <linux/spinlock.h>
27#include <linux/threads.h>
28#include <linux/cpumask.h>
29#include <linux/seqlock.h>
30
31/*
32 * Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT.
33 * In theory, it should be possible to add more levels straightforwardly.
34 * In practice, this did work well going from three levels to four.
35 * Of course, your mileage may vary.
36 */
37#define MAX_RCU_LVLS 4
38#if CONFIG_RCU_FANOUT > 16
39#define RCU_FANOUT_LEAF 16
40#else /* #if CONFIG_RCU_FANOUT > 16 */
41#define RCU_FANOUT_LEAF (CONFIG_RCU_FANOUT)
42#endif /* #else #if CONFIG_RCU_FANOUT > 16 */
43#define RCU_FANOUT_1 (RCU_FANOUT_LEAF)
44#define RCU_FANOUT_2 (RCU_FANOUT_1 * CONFIG_RCU_FANOUT)
45#define RCU_FANOUT_3 (RCU_FANOUT_2 * CONFIG_RCU_FANOUT)
46#define RCU_FANOUT_4 (RCU_FANOUT_3 * CONFIG_RCU_FANOUT)
47
48#if NR_CPUS <= RCU_FANOUT_1
49# define NUM_RCU_LVLS 1
50# define NUM_RCU_LVL_0 1
51# define NUM_RCU_LVL_1 (NR_CPUS)
52# define NUM_RCU_LVL_2 0
53# define NUM_RCU_LVL_3 0
54# define NUM_RCU_LVL_4 0
55#elif NR_CPUS <= RCU_FANOUT_2
56# define NUM_RCU_LVLS 2
57# define NUM_RCU_LVL_0 1
58# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
59# define NUM_RCU_LVL_2 (NR_CPUS)
60# define NUM_RCU_LVL_3 0
61# define NUM_RCU_LVL_4 0
62#elif NR_CPUS <= RCU_FANOUT_3
63# define NUM_RCU_LVLS 3
64# define NUM_RCU_LVL_0 1
65# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
66# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
67# define NUM_RCU_LVL_3 (NR_CPUS)
68# define NUM_RCU_LVL_4 0
69#elif NR_CPUS <= RCU_FANOUT_4
70# define NUM_RCU_LVLS 4
71# define NUM_RCU_LVL_0 1
72# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
73# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
74# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
75# define NUM_RCU_LVL_4 (NR_CPUS)
76#else
77# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
78#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
79
80#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3 + NUM_RCU_LVL_4)
81#define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
82
83/*
84 * Dynticks per-CPU state.
85 */
86struct rcu_dynticks {
87    int dynticks_nesting; /* Track irq/process nesting level. */
88    int dynticks_nmi_nesting; /* Track NMI nesting level. */
89    atomic_t dynticks; /* Even value for dynticks-idle, else odd. */
90};
91
92/* RCU's kthread states for tracing. */
93#define RCU_KTHREAD_STOPPED 0
94#define RCU_KTHREAD_RUNNING 1
95#define RCU_KTHREAD_WAITING 2
96#define RCU_KTHREAD_OFFCPU 3
97#define RCU_KTHREAD_YIELDING 4
98#define RCU_KTHREAD_MAX 4
99
100/*
101 * Definition for node within the RCU grace-period-detection hierarchy.
102 */
103struct rcu_node {
104    raw_spinlock_t lock; /* Root rcu_node's lock protects some */
105                /* rcu_state fields as well as following. */
106    unsigned long gpnum; /* Current grace period for this node. */
107                /* This will either be equal to or one */
108                /* behind the root rcu_node's gpnum. */
109    unsigned long completed; /* Last GP completed for this node. */
110                /* This will either be equal to or one */
111                /* behind the root rcu_node's gpnum. */
112    unsigned long qsmask; /* CPUs or groups that need to switch in */
113                /* order for current grace period to proceed.*/
114                /* In leaf rcu_node, each bit corresponds to */
115                /* an rcu_data structure, otherwise, each */
116                /* bit corresponds to a child rcu_node */
117                /* structure. */
118    unsigned long expmask; /* Groups that have ->blkd_tasks */
119                /* elements that need to drain to allow the */
120                /* current expedited grace period to */
121                /* complete (only for TREE_PREEMPT_RCU). */
122    atomic_t wakemask; /* CPUs whose kthread needs to be awakened. */
123                /* Since this has meaning only for leaf */
124                /* rcu_node structures, 32 bits suffices. */
125    unsigned long qsmaskinit;
126                /* Per-GP initial value for qsmask & expmask. */
127    unsigned long grpmask; /* Mask to apply to parent qsmask. */
128                /* Only one bit will be set in this mask. */
129    int grplo; /* lowest-numbered CPU or group here. */
130    int grphi; /* highest-numbered CPU or group here. */
131    u8 grpnum; /* CPU/group number for next level up. */
132    u8 level; /* root is at level 0. */
133    struct rcu_node *parent;
134    struct list_head blkd_tasks;
135                /* Tasks blocked in RCU read-side critical */
136                /* section. Tasks are placed at the head */
137                /* of this list and age towards the tail. */
138    struct list_head *gp_tasks;
139                /* Pointer to the first task blocking the */
140                /* current grace period, or NULL if there */
141                /* is no such task. */
142    struct list_head *exp_tasks;
143                /* Pointer to the first task blocking the */
144                /* current expedited grace period, or NULL */
145                /* if there is no such task. If there */
146                /* is no current expedited grace period, */
147                /* then there can cannot be any such task. */
148#ifdef CONFIG_RCU_BOOST
149    struct list_head *boost_tasks;
150                /* Pointer to first task that needs to be */
151                /* priority boosted, or NULL if no priority */
152                /* boosting is needed for this rcu_node */
153                /* structure. If there are no tasks */
154                /* queued on this rcu_node structure that */
155                /* are blocking the current grace period, */
156                /* there can be no such task. */
157    unsigned long boost_time;
158                /* When to start boosting (jiffies). */
159    struct task_struct *boost_kthread_task;
160                /* kthread that takes care of priority */
161                /* boosting for this rcu_node structure. */
162    unsigned int boost_kthread_status;
163                /* State of boost_kthread_task for tracing. */
164    unsigned long n_tasks_boosted;
165                /* Total number of tasks boosted. */
166    unsigned long n_exp_boosts;
167                /* Number of tasks boosted for expedited GP. */
168    unsigned long n_normal_boosts;
169                /* Number of tasks boosted for normal GP. */
170    unsigned long n_balk_blkd_tasks;
171                /* Refused to boost: no blocked tasks. */
172    unsigned long n_balk_exp_gp_tasks;
173                /* Refused to boost: nothing blocking GP. */
174    unsigned long n_balk_boost_tasks;
175                /* Refused to boost: already boosting. */
176    unsigned long n_balk_notblocked;
177                /* Refused to boost: RCU RS CS still running. */
178    unsigned long n_balk_notyet;
179                /* Refused to boost: not yet time. */
180    unsigned long n_balk_nos;
181                /* Refused to boost: not sure why, though. */
182                /* This can happen due to race conditions. */
183#endif /* #ifdef CONFIG_RCU_BOOST */
184    struct task_struct *node_kthread_task;
185                /* kthread that takes care of this rcu_node */
186                /* structure, for example, awakening the */
187                /* per-CPU kthreads as needed. */
188    unsigned int node_kthread_status;
189                /* State of node_kthread_task for tracing. */
190} ____cacheline_internodealigned_in_smp;
191
192/*
193 * Do a full breadth-first scan of the rcu_node structures for the
194 * specified rcu_state structure.
195 */
196#define rcu_for_each_node_breadth_first(rsp, rnp) \
197    for ((rnp) = &(rsp)->node[0]; \
198         (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
199
200/*
201 * Do a breadth-first scan of the non-leaf rcu_node structures for the
202 * specified rcu_state structure. Note that if there is a singleton
203 * rcu_node tree with but one rcu_node structure, this loop is a no-op.
204 */
205#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
206    for ((rnp) = &(rsp)->node[0]; \
207         (rnp) < (rsp)->level[NUM_RCU_LVLS - 1]; (rnp)++)
208
209/*
210 * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
211 * structure. Note that if there is a singleton rcu_node tree with but
212 * one rcu_node structure, this loop -will- visit the rcu_node structure.
213 * It is still a leaf node, even if it is also the root node.
214 */
215#define rcu_for_each_leaf_node(rsp, rnp) \
216    for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \
217         (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
218
219/* Index values for nxttail array in struct rcu_data. */
220#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
221#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
222#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
223#define RCU_NEXT_TAIL 3
224#define RCU_NEXT_SIZE 4
225
226/* Per-CPU data for read-copy update. */
227struct rcu_data {
228    /* 1) quiescent-state and grace-period handling : */
229    unsigned long completed; /* Track rsp->completed gp number */
230                    /* in order to detect GP end. */
231    unsigned long gpnum; /* Highest gp number that this CPU */
232                    /* is aware of having started. */
233    unsigned long passed_quiesc_completed;
234                    /* Value of completed at time of qs. */
235    bool passed_quiesc; /* User-mode/idle loop etc. */
236    bool qs_pending; /* Core waits for quiesc state. */
237    bool beenonline; /* CPU online at least once. */
238    bool preemptible; /* Preemptible RCU? */
239    struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
240    unsigned long grpmask; /* Mask to apply to leaf qsmask. */
241
242    /* 2) batch handling */
243    /*
244     * If nxtlist is not NULL, it is partitioned as follows.
245     * Any of the partitions might be empty, in which case the
246     * pointer to that partition will be equal to the pointer for
247     * the following partition. When the list is empty, all of
248     * the nxttail elements point to the ->nxtlist pointer itself,
249     * which in that case is NULL.
250     *
251     * [nxtlist, *nxttail[RCU_DONE_TAIL]):
252     * Entries that batch # <= ->completed
253     * The grace period for these entries has completed, and
254     * the other grace-period-completed entries may be moved
255     * here temporarily in rcu_process_callbacks().
256     * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
257     * Entries that batch # <= ->completed - 1: waiting for current GP
258     * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
259     * Entries known to have arrived before current GP ended
260     * [*nxttail[RCU_NEXT_READY_TAIL], *nxttail[RCU_NEXT_TAIL]):
261     * Entries that might have arrived after current GP ended
262     * Note that the value of *nxttail[RCU_NEXT_TAIL] will
263     * always be NULL, as this is the end of the list.
264     */
265    struct rcu_head *nxtlist;
266    struct rcu_head **nxttail[RCU_NEXT_SIZE];
267    long qlen; /* # of queued callbacks */
268    long qlen_last_fqs_check;
269                    /* qlen at last check for QS forcing */
270    unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */
271    unsigned long n_cbs_orphaned; /* RCU cbs orphaned by dying CPU */
272    unsigned long n_cbs_adopted; /* RCU cbs adopted from dying CPU */
273    unsigned long n_force_qs_snap;
274                    /* did other CPU force QS recently? */
275    long blimit; /* Upper limit on a processed batch */
276
277#ifdef CONFIG_NO_HZ
278    /* 3) dynticks interface. */
279    struct rcu_dynticks *dynticks; /* Shared per-CPU dynticks state. */
280    int dynticks_snap; /* Per-GP tracking for dynticks. */
281#endif /* #ifdef CONFIG_NO_HZ */
282
283    /* 4) reasons this CPU needed to be kicked by force_quiescent_state */
284#ifdef CONFIG_NO_HZ
285    unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */
286#endif /* #ifdef CONFIG_NO_HZ */
287    unsigned long offline_fqs; /* Kicked due to being offline. */
288    unsigned long resched_ipi; /* Sent a resched IPI. */
289
290    /* 5) __rcu_pending() statistics. */
291    unsigned long n_rcu_pending; /* rcu_pending() calls since boot. */
292    unsigned long n_rp_qs_pending;
293    unsigned long n_rp_report_qs;
294    unsigned long n_rp_cb_ready;
295    unsigned long n_rp_cpu_needs_gp;
296    unsigned long n_rp_gp_completed;
297    unsigned long n_rp_gp_started;
298    unsigned long n_rp_need_fqs;
299    unsigned long n_rp_need_nothing;
300
301    int cpu;
302};
303
304/* Values for signaled field in struct rcu_state. */
305#define RCU_GP_IDLE 0 /* No grace period in progress. */
306#define RCU_GP_INIT 1 /* Grace period being initialized. */
307#define RCU_SAVE_DYNTICK 2 /* Need to scan dyntick state. */
308#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
309#ifdef CONFIG_NO_HZ
310#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
311#else /* #ifdef CONFIG_NO_HZ */
312#define RCU_SIGNAL_INIT RCU_FORCE_QS
313#endif /* #else #ifdef CONFIG_NO_HZ */
314
315#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
316
317#ifdef CONFIG_PROVE_RCU
318#define RCU_STALL_DELAY_DELTA (5 * HZ)
319#else
320#define RCU_STALL_DELAY_DELTA 0
321#endif
322
323#define RCU_SECONDS_TILL_STALL_CHECK (CONFIG_RCU_CPU_STALL_TIMEOUT * HZ + \
324                    RCU_STALL_DELAY_DELTA)
325                        /* for rsp->jiffies_stall */
326#define RCU_SECONDS_TILL_STALL_RECHECK (3 * RCU_SECONDS_TILL_STALL_CHECK + 30)
327                        /* for rsp->jiffies_stall */
328#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
329                        /* to take at least one */
330                        /* scheduling clock irq */
331                        /* before ratting on them. */
332
333#define rcu_wait(cond) \
334do { \
335    for (;;) { \
336        set_current_state(TASK_INTERRUPTIBLE); \
337        if (cond) \
338            break; \
339        schedule(); \
340    } \
341    __set_current_state(TASK_RUNNING); \
342} while (0)
343
344/*
345 * RCU global state, including node hierarchy. This hierarchy is
346 * represented in "heap" form in a dense array. The root (first level)
347 * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
348 * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
349 * and the third level in ->node[m+1] and following (->node[m+1] referenced
350 * by ->level[2]). The number of levels is determined by the number of
351 * CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy"
352 * consisting of a single rcu_node.
353 */
354struct rcu_state {
355    struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
356    struct rcu_node *level[NUM_RCU_LVLS]; /* Hierarchy levels. */
357    u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */
358    u8 levelspread[NUM_RCU_LVLS]; /* kids/node in each level. */
359    struct rcu_data __percpu *rda; /* pointer of percu rcu_data. */
360
361    /* The following fields are guarded by the root rcu_node's lock. */
362
363    u8 signaled ____cacheline_internodealigned_in_smp;
364                        /* Force QS state. */
365    u8 fqs_active; /* force_quiescent_state() */
366                        /* is running. */
367    u8 fqs_need_gp; /* A CPU was prevented from */
368                        /* starting a new grace */
369                        /* period because */
370                        /* force_quiescent_state() */
371                        /* was running. */
372    u8 boost; /* Subject to priority boost. */
373    unsigned long gpnum; /* Current gp number. */
374    unsigned long completed; /* # of last completed gp. */
375
376    /* End of fields guarded by root rcu_node's lock. */
377
378    raw_spinlock_t onofflock; /* exclude on/offline and */
379                        /* starting new GP. */
380    raw_spinlock_t fqslock; /* Only one task forcing */
381                        /* quiescent states. */
382    unsigned long jiffies_force_qs; /* Time at which to invoke */
383                        /* force_quiescent_state(). */
384    unsigned long n_force_qs; /* Number of calls to */
385                        /* force_quiescent_state(). */
386    unsigned long n_force_qs_lh; /* ~Number of calls leaving */
387                        /* due to lock unavailable. */
388    unsigned long n_force_qs_ngp; /* Number of calls leaving */
389                        /* due to no GP active. */
390    unsigned long gp_start; /* Time at which GP started, */
391                        /* but in jiffies. */
392    unsigned long jiffies_stall; /* Time at which to check */
393                        /* for CPU stalls. */
394    unsigned long gp_max; /* Maximum GP duration in */
395                        /* jiffies. */
396    char *name; /* Name of structure. */
397};
398
399/* Return values for rcu_preempt_offline_tasks(). */
400
401#define RCU_OFL_TASKS_NORM_GP 0x1 /* Tasks blocking normal */
402                        /* GP were moved to root. */
403#define RCU_OFL_TASKS_EXP_GP 0x2 /* Tasks blocking expedited */
404                        /* GP were moved to root. */
405
406/*
407 * RCU implementation internal declarations:
408 */
409extern struct rcu_state rcu_sched_state;
410DECLARE_PER_CPU(struct rcu_data, rcu_sched_data);
411
412extern struct rcu_state rcu_bh_state;
413DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
414
415#ifdef CONFIG_TREE_PREEMPT_RCU
416extern struct rcu_state rcu_preempt_state;
417DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data);
418#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
419
420#ifndef RCU_TREE_NONCORE
421
422/* Forward declarations for rcutree_plugin.h */
423static void rcu_bootup_announce(void);
424long rcu_batches_completed(void);
425static void rcu_preempt_note_context_switch(int cpu);
426static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
427#ifdef CONFIG_HOTPLUG_CPU
428static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
429                      unsigned long flags);
430static void rcu_stop_cpu_kthread(int cpu);
431#endif /* #ifdef CONFIG_HOTPLUG_CPU */
432static void rcu_print_detail_task_stall(struct rcu_state *rsp);
433static void rcu_print_task_stall(struct rcu_node *rnp);
434static void rcu_preempt_stall_reset(void);
435static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
436#ifdef CONFIG_HOTPLUG_CPU
437static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
438                     struct rcu_node *rnp,
439                     struct rcu_data *rdp);
440static void rcu_preempt_offline_cpu(int cpu);
441#endif /* #ifdef CONFIG_HOTPLUG_CPU */
442static void rcu_preempt_check_callbacks(int cpu);
443static void rcu_preempt_process_callbacks(void);
444void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
445#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
446static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
447#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */
448static int rcu_preempt_pending(int cpu);
449static int rcu_preempt_needs_cpu(int cpu);
450static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
451static void rcu_preempt_send_cbs_to_online(void);
452static void __init __rcu_init_preempt(void);
453static void rcu_needs_cpu_flush(void);
454static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
455static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
456static void invoke_rcu_callbacks_kthread(void);
457#ifdef CONFIG_RCU_BOOST
458static void rcu_preempt_do_callbacks(void);
459static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
460                      cpumask_var_t cm);
461static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
462                         struct rcu_node *rnp,
463                         int rnp_index);
464static void invoke_rcu_node_kthread(struct rcu_node *rnp);
465static void rcu_yield(void (*f)(unsigned long), unsigned long arg);
466#endif /* #ifdef CONFIG_RCU_BOOST */
467static void rcu_cpu_kthread_setrt(int cpu, int to_rt);
468static void __cpuinit rcu_prepare_kthreads(int cpu);
469
470#endif /* #ifndef RCU_TREE_NONCORE */
471

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