Root/block/blk-ioc.c

1/*
2 * Functions related to io context handling
3 */
4#include <linux/kernel.h>
5#include <linux/module.h>
6#include <linux/init.h>
7#include <linux/bio.h>
8#include <linux/blkdev.h>
9#include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
10#include <linux/slab.h>
11
12#include "blk.h"
13
14/*
15 * For io context allocations
16 */
17static struct kmem_cache *iocontext_cachep;
18
19/**
20 * get_io_context - increment reference count to io_context
21 * @ioc: io_context to get
22 *
23 * Increment reference count to @ioc.
24 */
25void get_io_context(struct io_context *ioc)
26{
27    BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
28    atomic_long_inc(&ioc->refcount);
29}
30EXPORT_SYMBOL(get_io_context);
31
32static void icq_free_icq_rcu(struct rcu_head *head)
33{
34    struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
35
36    kmem_cache_free(icq->__rcu_icq_cache, icq);
37}
38
39/* Exit an icq. Called with both ioc and q locked. */
40static void ioc_exit_icq(struct io_cq *icq)
41{
42    struct elevator_type *et = icq->q->elevator->type;
43
44    if (icq->flags & ICQ_EXITED)
45        return;
46
47    if (et->ops.elevator_exit_icq_fn)
48        et->ops.elevator_exit_icq_fn(icq);
49
50    icq->flags |= ICQ_EXITED;
51}
52
53/* Release an icq. Called with both ioc and q locked. */
54static void ioc_destroy_icq(struct io_cq *icq)
55{
56    struct io_context *ioc = icq->ioc;
57    struct request_queue *q = icq->q;
58    struct elevator_type *et = q->elevator->type;
59
60    lockdep_assert_held(&ioc->lock);
61    lockdep_assert_held(q->queue_lock);
62
63    radix_tree_delete(&ioc->icq_tree, icq->q->id);
64    hlist_del_init(&icq->ioc_node);
65    list_del_init(&icq->q_node);
66
67    /*
68     * Both setting lookup hint to and clearing it from @icq are done
69     * under queue_lock. If it's not pointing to @icq now, it never
70     * will. Hint assignment itself can race safely.
71     */
72    if (rcu_dereference_raw(ioc->icq_hint) == icq)
73        rcu_assign_pointer(ioc->icq_hint, NULL);
74
75    ioc_exit_icq(icq);
76
77    /*
78     * @icq->q might have gone away by the time RCU callback runs
79     * making it impossible to determine icq_cache. Record it in @icq.
80     */
81    icq->__rcu_icq_cache = et->icq_cache;
82    call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
83}
84
85/*
86 * Slow path for ioc release in put_io_context(). Performs double-lock
87 * dancing to unlink all icq's and then frees ioc.
88 */
89static void ioc_release_fn(struct work_struct *work)
90{
91    struct io_context *ioc = container_of(work, struct io_context,
92                          release_work);
93    unsigned long flags;
94
95    /*
96     * Exiting icq may call into put_io_context() through elevator
97     * which will trigger lockdep warning. The ioc's are guaranteed to
98     * be different, use a different locking subclass here. Use
99     * irqsave variant as there's no spin_lock_irq_nested().
100     */
101    spin_lock_irqsave_nested(&ioc->lock, flags, 1);
102
103    while (!hlist_empty(&ioc->icq_list)) {
104        struct io_cq *icq = hlist_entry(ioc->icq_list.first,
105                        struct io_cq, ioc_node);
106        struct request_queue *q = icq->q;
107
108        if (spin_trylock(q->queue_lock)) {
109            ioc_destroy_icq(icq);
110            spin_unlock(q->queue_lock);
111        } else {
112            spin_unlock_irqrestore(&ioc->lock, flags);
113            cpu_relax();
114            spin_lock_irqsave_nested(&ioc->lock, flags, 1);
115        }
116    }
117
118    spin_unlock_irqrestore(&ioc->lock, flags);
119
120    kmem_cache_free(iocontext_cachep, ioc);
121}
122
123/**
124 * put_io_context - put a reference of io_context
125 * @ioc: io_context to put
126 *
127 * Decrement reference count of @ioc and release it if the count reaches
128 * zero.
129 */
130void put_io_context(struct io_context *ioc)
131{
132    unsigned long flags;
133    bool free_ioc = false;
134
135    if (ioc == NULL)
136        return;
137
138    BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
139
140    /*
141     * Releasing ioc requires reverse order double locking and we may
142     * already be holding a queue_lock. Do it asynchronously from wq.
143     */
144    if (atomic_long_dec_and_test(&ioc->refcount)) {
145        spin_lock_irqsave(&ioc->lock, flags);
146        if (!hlist_empty(&ioc->icq_list))
147            schedule_work(&ioc->release_work);
148        else
149            free_ioc = true;
150        spin_unlock_irqrestore(&ioc->lock, flags);
151    }
152
153    if (free_ioc)
154        kmem_cache_free(iocontext_cachep, ioc);
155}
156EXPORT_SYMBOL(put_io_context);
157
158/**
159 * put_io_context_active - put active reference on ioc
160 * @ioc: ioc of interest
161 *
162 * Undo get_io_context_active(). If active reference reaches zero after
163 * put, @ioc can never issue further IOs and ioscheds are notified.
164 */
165void put_io_context_active(struct io_context *ioc)
166{
167    unsigned long flags;
168    struct io_cq *icq;
169
170    if (!atomic_dec_and_test(&ioc->active_ref)) {
171        put_io_context(ioc);
172        return;
173    }
174
175    /*
176     * Need ioc lock to walk icq_list and q lock to exit icq. Perform
177     * reverse double locking. Read comment in ioc_release_fn() for
178     * explanation on the nested locking annotation.
179     */
180retry:
181    spin_lock_irqsave_nested(&ioc->lock, flags, 1);
182    hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
183        if (icq->flags & ICQ_EXITED)
184            continue;
185        if (spin_trylock(icq->q->queue_lock)) {
186            ioc_exit_icq(icq);
187            spin_unlock(icq->q->queue_lock);
188        } else {
189            spin_unlock_irqrestore(&ioc->lock, flags);
190            cpu_relax();
191            goto retry;
192        }
193    }
194    spin_unlock_irqrestore(&ioc->lock, flags);
195
196    put_io_context(ioc);
197}
198
199/* Called by the exiting task */
200void exit_io_context(struct task_struct *task)
201{
202    struct io_context *ioc;
203
204    task_lock(task);
205    ioc = task->io_context;
206    task->io_context = NULL;
207    task_unlock(task);
208
209    atomic_dec(&ioc->nr_tasks);
210    put_io_context_active(ioc);
211}
212
213/**
214 * ioc_clear_queue - break any ioc association with the specified queue
215 * @q: request_queue being cleared
216 *
217 * Walk @q->icq_list and exit all io_cq's. Must be called with @q locked.
218 */
219void ioc_clear_queue(struct request_queue *q)
220{
221    lockdep_assert_held(q->queue_lock);
222
223    while (!list_empty(&q->icq_list)) {
224        struct io_cq *icq = list_entry(q->icq_list.next,
225                           struct io_cq, q_node);
226        struct io_context *ioc = icq->ioc;
227
228        spin_lock(&ioc->lock);
229        ioc_destroy_icq(icq);
230        spin_unlock(&ioc->lock);
231    }
232}
233
234int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
235{
236    struct io_context *ioc;
237    int ret;
238
239    ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
240                    node);
241    if (unlikely(!ioc))
242        return -ENOMEM;
243
244    /* initialize */
245    atomic_long_set(&ioc->refcount, 1);
246    atomic_set(&ioc->nr_tasks, 1);
247    atomic_set(&ioc->active_ref, 1);
248    spin_lock_init(&ioc->lock);
249    INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
250    INIT_HLIST_HEAD(&ioc->icq_list);
251    INIT_WORK(&ioc->release_work, ioc_release_fn);
252
253    /*
254     * Try to install. ioc shouldn't be installed if someone else
255     * already did or @task, which isn't %current, is exiting. Note
256     * that we need to allow ioc creation on exiting %current as exit
257     * path may issue IOs from e.g. exit_files(). The exit path is
258     * responsible for not issuing IO after exit_io_context().
259     */
260    task_lock(task);
261    if (!task->io_context &&
262        (task == current || !(task->flags & PF_EXITING)))
263        task->io_context = ioc;
264    else
265        kmem_cache_free(iocontext_cachep, ioc);
266
267    ret = task->io_context ? 0 : -EBUSY;
268
269    task_unlock(task);
270
271    return ret;
272}
273
274/**
275 * get_task_io_context - get io_context of a task
276 * @task: task of interest
277 * @gfp_flags: allocation flags, used if allocation is necessary
278 * @node: allocation node, used if allocation is necessary
279 *
280 * Return io_context of @task. If it doesn't exist, it is created with
281 * @gfp_flags and @node. The returned io_context has its reference count
282 * incremented.
283 *
284 * This function always goes through task_lock() and it's better to use
285 * %current->io_context + get_io_context() for %current.
286 */
287struct io_context *get_task_io_context(struct task_struct *task,
288                       gfp_t gfp_flags, int node)
289{
290    struct io_context *ioc;
291
292    might_sleep_if(gfp_flags & __GFP_WAIT);
293
294    do {
295        task_lock(task);
296        ioc = task->io_context;
297        if (likely(ioc)) {
298            get_io_context(ioc);
299            task_unlock(task);
300            return ioc;
301        }
302        task_unlock(task);
303    } while (!create_task_io_context(task, gfp_flags, node));
304
305    return NULL;
306}
307EXPORT_SYMBOL(get_task_io_context);
308
309/**
310 * ioc_lookup_icq - lookup io_cq from ioc
311 * @ioc: the associated io_context
312 * @q: the associated request_queue
313 *
314 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
315 * with @q->queue_lock held.
316 */
317struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
318{
319    struct io_cq *icq;
320
321    lockdep_assert_held(q->queue_lock);
322
323    /*
324     * icq's are indexed from @ioc using radix tree and hint pointer,
325     * both of which are protected with RCU. All removals are done
326     * holding both q and ioc locks, and we're holding q lock - if we
327     * find a icq which points to us, it's guaranteed to be valid.
328     */
329    rcu_read_lock();
330    icq = rcu_dereference(ioc->icq_hint);
331    if (icq && icq->q == q)
332        goto out;
333
334    icq = radix_tree_lookup(&ioc->icq_tree, q->id);
335    if (icq && icq->q == q)
336        rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
337    else
338        icq = NULL;
339out:
340    rcu_read_unlock();
341    return icq;
342}
343EXPORT_SYMBOL(ioc_lookup_icq);
344
345/**
346 * ioc_create_icq - create and link io_cq
347 * @ioc: io_context of interest
348 * @q: request_queue of interest
349 * @gfp_mask: allocation mask
350 *
351 * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
352 * will be created using @gfp_mask.
353 *
354 * The caller is responsible for ensuring @ioc won't go away and @q is
355 * alive and will stay alive until this function returns.
356 */
357struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
358                 gfp_t gfp_mask)
359{
360    struct elevator_type *et = q->elevator->type;
361    struct io_cq *icq;
362
363    /* allocate stuff */
364    icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
365                    q->node);
366    if (!icq)
367        return NULL;
368
369    if (radix_tree_preload(gfp_mask) < 0) {
370        kmem_cache_free(et->icq_cache, icq);
371        return NULL;
372    }
373
374    icq->ioc = ioc;
375    icq->q = q;
376    INIT_LIST_HEAD(&icq->q_node);
377    INIT_HLIST_NODE(&icq->ioc_node);
378
379    /* lock both q and ioc and try to link @icq */
380    spin_lock_irq(q->queue_lock);
381    spin_lock(&ioc->lock);
382
383    if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
384        hlist_add_head(&icq->ioc_node, &ioc->icq_list);
385        list_add(&icq->q_node, &q->icq_list);
386        if (et->ops.elevator_init_icq_fn)
387            et->ops.elevator_init_icq_fn(icq);
388    } else {
389        kmem_cache_free(et->icq_cache, icq);
390        icq = ioc_lookup_icq(ioc, q);
391        if (!icq)
392            printk(KERN_ERR "cfq: icq link failed!\n");
393    }
394
395    spin_unlock(&ioc->lock);
396    spin_unlock_irq(q->queue_lock);
397    radix_tree_preload_end();
398    return icq;
399}
400
401static int __init blk_ioc_init(void)
402{
403    iocontext_cachep = kmem_cache_create("blkdev_ioc",
404            sizeof(struct io_context), 0, SLAB_PANIC, NULL);
405    return 0;
406}
407subsys_initcall(blk_ioc_init);
408

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