1 // SPDX-License-Identifier: GPL-2.0
3 * Functions related to io context handling
5 #include <linux/kernel.h>
6 #include <linux/module.h>
7 #include <linux/init.h>
9 #include <linux/blkdev.h>
10 #include <linux/slab.h>
11 #include <linux/sched/task.h>
16 * For io context allocations
18 static struct kmem_cache *iocontext_cachep;
21 * get_io_context - increment reference count to io_context
22 * @ioc: io_context to get
24 * Increment reference count to @ioc.
26 void get_io_context(struct io_context *ioc)
28 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
29 atomic_long_inc(&ioc->refcount);
31 EXPORT_SYMBOL(get_io_context);
33 static void icq_free_icq_rcu(struct rcu_head *head)
35 struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
37 kmem_cache_free(icq->__rcu_icq_cache, icq);
41 * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
42 * and queue locked for legacy.
44 static void ioc_exit_icq(struct io_cq *icq)
46 struct elevator_type *et = icq->q->elevator->type;
48 if (icq->flags & ICQ_EXITED)
51 if (et->uses_mq && et->ops.mq.exit_icq)
52 et->ops.mq.exit_icq(icq);
53 else if (!et->uses_mq && et->ops.sq.elevator_exit_icq_fn)
54 et->ops.sq.elevator_exit_icq_fn(icq);
56 icq->flags |= ICQ_EXITED;
60 * Release an icq. Called with ioc locked for blk-mq, and with both ioc
61 * and queue locked for legacy.
63 static void ioc_destroy_icq(struct io_cq *icq)
65 struct io_context *ioc = icq->ioc;
66 struct request_queue *q = icq->q;
67 struct elevator_type *et = q->elevator->type;
69 lockdep_assert_held(&ioc->lock);
71 radix_tree_delete(&ioc->icq_tree, icq->q->id);
72 hlist_del_init(&icq->ioc_node);
73 list_del_init(&icq->q_node);
76 * Both setting lookup hint to and clearing it from @icq are done
77 * under queue_lock. If it's not pointing to @icq now, it never
78 * will. Hint assignment itself can race safely.
80 if (rcu_access_pointer(ioc->icq_hint) == icq)
81 rcu_assign_pointer(ioc->icq_hint, NULL);
86 * @icq->q might have gone away by the time RCU callback runs
87 * making it impossible to determine icq_cache. Record it in @icq.
89 icq->__rcu_icq_cache = et->icq_cache;
90 icq->flags |= ICQ_DESTROYED;
91 call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
95 * Slow path for ioc release in put_io_context(). Performs double-lock
96 * dancing to unlink all icq's and then frees ioc.
98 static void ioc_release_fn(struct work_struct *work)
100 struct io_context *ioc = container_of(work, struct io_context,
105 * Exiting icq may call into put_io_context() through elevator
106 * which will trigger lockdep warning. The ioc's are guaranteed to
107 * be different, use a different locking subclass here. Use
108 * irqsave variant as there's no spin_lock_irq_nested().
110 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
112 while (!hlist_empty(&ioc->icq_list)) {
113 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
114 struct io_cq, ioc_node);
115 struct request_queue *q = icq->q;
117 if (spin_trylock(q->queue_lock)) {
118 ioc_destroy_icq(icq);
119 spin_unlock(q->queue_lock);
121 spin_unlock_irqrestore(&ioc->lock, flags);
123 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
127 spin_unlock_irqrestore(&ioc->lock, flags);
129 kmem_cache_free(iocontext_cachep, ioc);
133 * put_io_context - put a reference of io_context
134 * @ioc: io_context to put
136 * Decrement reference count of @ioc and release it if the count reaches
139 void put_io_context(struct io_context *ioc)
142 bool free_ioc = false;
147 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
150 * Releasing ioc requires reverse order double locking and we may
151 * already be holding a queue_lock. Do it asynchronously from wq.
153 if (atomic_long_dec_and_test(&ioc->refcount)) {
154 spin_lock_irqsave(&ioc->lock, flags);
155 if (!hlist_empty(&ioc->icq_list))
156 queue_work(system_power_efficient_wq,
160 spin_unlock_irqrestore(&ioc->lock, flags);
164 kmem_cache_free(iocontext_cachep, ioc);
166 EXPORT_SYMBOL(put_io_context);
169 * put_io_context_active - put active reference on ioc
170 * @ioc: ioc of interest
172 * Undo get_io_context_active(). If active reference reaches zero after
173 * put, @ioc can never issue further IOs and ioscheds are notified.
175 void put_io_context_active(struct io_context *ioc)
177 struct elevator_type *et;
181 if (!atomic_dec_and_test(&ioc->active_ref)) {
187 * Need ioc lock to walk icq_list and q lock to exit icq. Perform
188 * reverse double locking. Read comment in ioc_release_fn() for
189 * explanation on the nested locking annotation.
192 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
193 hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
194 if (icq->flags & ICQ_EXITED)
197 et = icq->q->elevator->type;
201 if (spin_trylock(icq->q->queue_lock)) {
203 spin_unlock(icq->q->queue_lock);
205 spin_unlock_irqrestore(&ioc->lock, flags);
211 spin_unlock_irqrestore(&ioc->lock, flags);
216 /* Called by the exiting task */
217 void exit_io_context(struct task_struct *task)
219 struct io_context *ioc;
222 ioc = task->io_context;
223 task->io_context = NULL;
226 atomic_dec(&ioc->nr_tasks);
227 put_io_context_active(ioc);
230 static void __ioc_clear_queue(struct list_head *icq_list)
235 while (!list_empty(icq_list)) {
236 struct io_cq *icq = list_entry(icq_list->next,
237 struct io_cq, q_node);
238 struct io_context *ioc = icq->ioc;
240 spin_lock_irqsave(&ioc->lock, flags);
241 if (icq->flags & ICQ_DESTROYED) {
242 spin_unlock_irqrestore(&ioc->lock, flags);
245 ioc_destroy_icq(icq);
246 spin_unlock_irqrestore(&ioc->lock, flags);
252 * ioc_clear_queue - break any ioc association with the specified queue
253 * @q: request_queue being cleared
255 * Walk @q->icq_list and exit all io_cq's.
257 void ioc_clear_queue(struct request_queue *q)
261 spin_lock_irq(q->queue_lock);
262 list_splice_init(&q->icq_list, &icq_list);
265 spin_unlock_irq(q->queue_lock);
266 __ioc_clear_queue(&icq_list);
268 __ioc_clear_queue(&icq_list);
269 spin_unlock_irq(q->queue_lock);
273 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
275 struct io_context *ioc;
278 ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
284 atomic_long_set(&ioc->refcount, 1);
285 atomic_set(&ioc->nr_tasks, 1);
286 atomic_set(&ioc->active_ref, 1);
287 spin_lock_init(&ioc->lock);
288 INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
289 INIT_HLIST_HEAD(&ioc->icq_list);
290 INIT_WORK(&ioc->release_work, ioc_release_fn);
293 * Try to install. ioc shouldn't be installed if someone else
294 * already did or @task, which isn't %current, is exiting. Note
295 * that we need to allow ioc creation on exiting %current as exit
296 * path may issue IOs from e.g. exit_files(). The exit path is
297 * responsible for not issuing IO after exit_io_context().
300 if (!task->io_context &&
301 (task == current || !(task->flags & PF_EXITING)))
302 task->io_context = ioc;
304 kmem_cache_free(iocontext_cachep, ioc);
306 ret = task->io_context ? 0 : -EBUSY;
314 * get_task_io_context - get io_context of a task
315 * @task: task of interest
316 * @gfp_flags: allocation flags, used if allocation is necessary
317 * @node: allocation node, used if allocation is necessary
319 * Return io_context of @task. If it doesn't exist, it is created with
320 * @gfp_flags and @node. The returned io_context has its reference count
323 * This function always goes through task_lock() and it's better to use
324 * %current->io_context + get_io_context() for %current.
326 struct io_context *get_task_io_context(struct task_struct *task,
327 gfp_t gfp_flags, int node)
329 struct io_context *ioc;
331 might_sleep_if(gfpflags_allow_blocking(gfp_flags));
335 ioc = task->io_context;
342 } while (!create_task_io_context(task, gfp_flags, node));
346 EXPORT_SYMBOL(get_task_io_context);
349 * ioc_lookup_icq - lookup io_cq from ioc
350 * @ioc: the associated io_context
351 * @q: the associated request_queue
353 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
354 * with @q->queue_lock held.
356 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
360 lockdep_assert_held(q->queue_lock);
363 * icq's are indexed from @ioc using radix tree and hint pointer,
364 * both of which are protected with RCU. All removals are done
365 * holding both q and ioc locks, and we're holding q lock - if we
366 * find a icq which points to us, it's guaranteed to be valid.
369 icq = rcu_dereference(ioc->icq_hint);
370 if (icq && icq->q == q)
373 icq = radix_tree_lookup(&ioc->icq_tree, q->id);
374 if (icq && icq->q == q)
375 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
382 EXPORT_SYMBOL(ioc_lookup_icq);
385 * ioc_create_icq - create and link io_cq
386 * @ioc: io_context of interest
387 * @q: request_queue of interest
388 * @gfp_mask: allocation mask
390 * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
391 * will be created using @gfp_mask.
393 * The caller is responsible for ensuring @ioc won't go away and @q is
394 * alive and will stay alive until this function returns.
396 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
399 struct elevator_type *et = q->elevator->type;
403 icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
408 if (radix_tree_maybe_preload(gfp_mask) < 0) {
409 kmem_cache_free(et->icq_cache, icq);
415 INIT_LIST_HEAD(&icq->q_node);
416 INIT_HLIST_NODE(&icq->ioc_node);
418 /* lock both q and ioc and try to link @icq */
419 spin_lock_irq(q->queue_lock);
420 spin_lock(&ioc->lock);
422 if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
423 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
424 list_add(&icq->q_node, &q->icq_list);
425 if (et->uses_mq && et->ops.mq.init_icq)
426 et->ops.mq.init_icq(icq);
427 else if (!et->uses_mq && et->ops.sq.elevator_init_icq_fn)
428 et->ops.sq.elevator_init_icq_fn(icq);
430 kmem_cache_free(et->icq_cache, icq);
431 icq = ioc_lookup_icq(ioc, q);
433 printk(KERN_ERR "cfq: icq link failed!\n");
436 spin_unlock(&ioc->lock);
437 spin_unlock_irq(q->queue_lock);
438 radix_tree_preload_end();
442 static int __init blk_ioc_init(void)
444 iocontext_cachep = kmem_cache_create("blkdev_ioc",
445 sizeof(struct io_context), 0, SLAB_PANIC, NULL);
448 subsys_initcall(blk_ioc_init);