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);
32 static void icq_free_icq_rcu(struct rcu_head *head)
34 struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
36 kmem_cache_free(icq->__rcu_icq_cache, icq);
40 * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
41 * and queue locked for legacy.
43 static void ioc_exit_icq(struct io_cq *icq)
45 struct elevator_type *et = icq->q->elevator->type;
47 if (icq->flags & ICQ_EXITED)
51 et->ops.exit_icq(icq);
53 icq->flags |= ICQ_EXITED;
57 * Release an icq. Called with ioc locked for blk-mq, and with both ioc
58 * and queue locked for legacy.
60 static void ioc_destroy_icq(struct io_cq *icq)
62 struct io_context *ioc = icq->ioc;
63 struct request_queue *q = icq->q;
64 struct elevator_type *et = q->elevator->type;
66 lockdep_assert_held(&ioc->lock);
68 radix_tree_delete(&ioc->icq_tree, icq->q->id);
69 hlist_del_init(&icq->ioc_node);
70 list_del_init(&icq->q_node);
73 * Both setting lookup hint to and clearing it from @icq are done
74 * under queue_lock. If it's not pointing to @icq now, it never
75 * will. Hint assignment itself can race safely.
77 if (rcu_access_pointer(ioc->icq_hint) == icq)
78 rcu_assign_pointer(ioc->icq_hint, NULL);
83 * @icq->q might have gone away by the time RCU callback runs
84 * making it impossible to determine icq_cache. Record it in @icq.
86 icq->__rcu_icq_cache = et->icq_cache;
87 icq->flags |= ICQ_DESTROYED;
88 call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
92 * Slow path for ioc release in put_io_context(). Performs double-lock
93 * dancing to unlink all icq's and then frees ioc.
95 static void ioc_release_fn(struct work_struct *work)
97 struct io_context *ioc = container_of(work, struct io_context,
102 * Exiting icq may call into put_io_context() through elevator
103 * which will trigger lockdep warning. The ioc's are guaranteed to
104 * be different, use a different locking subclass here. Use
105 * irqsave variant as there's no spin_lock_irq_nested().
107 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
109 while (!hlist_empty(&ioc->icq_list)) {
110 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
111 struct io_cq, ioc_node);
112 struct request_queue *q = icq->q;
114 if (spin_trylock(&q->queue_lock)) {
115 ioc_destroy_icq(icq);
116 spin_unlock(&q->queue_lock);
118 spin_unlock_irqrestore(&ioc->lock, flags);
120 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
124 spin_unlock_irqrestore(&ioc->lock, flags);
126 kmem_cache_free(iocontext_cachep, ioc);
130 * put_io_context - put a reference of io_context
131 * @ioc: io_context to put
133 * Decrement reference count of @ioc and release it if the count reaches
136 void put_io_context(struct io_context *ioc)
139 bool free_ioc = false;
144 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
147 * Releasing ioc requires reverse order double locking and we may
148 * already be holding a queue_lock. Do it asynchronously from wq.
150 if (atomic_long_dec_and_test(&ioc->refcount)) {
151 spin_lock_irqsave(&ioc->lock, flags);
152 if (!hlist_empty(&ioc->icq_list))
153 queue_work(system_power_efficient_wq,
157 spin_unlock_irqrestore(&ioc->lock, flags);
161 kmem_cache_free(iocontext_cachep, ioc);
165 * put_io_context_active - put active reference on ioc
166 * @ioc: ioc of interest
168 * Undo get_io_context_active(). If active reference reaches zero after
169 * put, @ioc can never issue further IOs and ioscheds are notified.
171 void put_io_context_active(struct io_context *ioc)
176 if (!atomic_dec_and_test(&ioc->active_ref)) {
182 * Need ioc lock to walk icq_list and q lock to exit icq. Perform
183 * reverse double locking. Read comment in ioc_release_fn() for
184 * explanation on the nested locking annotation.
186 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
187 hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
188 if (icq->flags & ICQ_EXITED)
193 spin_unlock_irqrestore(&ioc->lock, flags);
198 /* Called by the exiting task */
199 void exit_io_context(struct task_struct *task)
201 struct io_context *ioc;
204 ioc = task->io_context;
205 task->io_context = NULL;
208 atomic_dec(&ioc->nr_tasks);
209 put_io_context_active(ioc);
212 static void __ioc_clear_queue(struct list_head *icq_list)
217 while (!list_empty(icq_list)) {
218 struct io_cq *icq = list_entry(icq_list->next,
219 struct io_cq, q_node);
220 struct io_context *ioc = icq->ioc;
222 spin_lock_irqsave(&ioc->lock, flags);
223 if (icq->flags & ICQ_DESTROYED) {
224 spin_unlock_irqrestore(&ioc->lock, flags);
227 ioc_destroy_icq(icq);
228 spin_unlock_irqrestore(&ioc->lock, flags);
234 * ioc_clear_queue - break any ioc association with the specified queue
235 * @q: request_queue being cleared
237 * Walk @q->icq_list and exit all io_cq's.
239 void ioc_clear_queue(struct request_queue *q)
243 spin_lock_irq(&q->queue_lock);
244 list_splice_init(&q->icq_list, &icq_list);
245 spin_unlock_irq(&q->queue_lock);
247 __ioc_clear_queue(&icq_list);
250 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
252 struct io_context *ioc;
255 ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
261 atomic_long_set(&ioc->refcount, 1);
262 atomic_set(&ioc->nr_tasks, 1);
263 atomic_set(&ioc->active_ref, 1);
264 spin_lock_init(&ioc->lock);
265 INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
266 INIT_HLIST_HEAD(&ioc->icq_list);
267 INIT_WORK(&ioc->release_work, ioc_release_fn);
270 * Try to install. ioc shouldn't be installed if someone else
271 * already did or @task, which isn't %current, is exiting. Note
272 * that we need to allow ioc creation on exiting %current as exit
273 * path may issue IOs from e.g. exit_files(). The exit path is
274 * responsible for not issuing IO after exit_io_context().
277 if (!task->io_context &&
278 (task == current || !(task->flags & PF_EXITING)))
279 task->io_context = ioc;
281 kmem_cache_free(iocontext_cachep, ioc);
283 ret = task->io_context ? 0 : -EBUSY;
291 * get_task_io_context - get io_context of a task
292 * @task: task of interest
293 * @gfp_flags: allocation flags, used if allocation is necessary
294 * @node: allocation node, used if allocation is necessary
296 * Return io_context of @task. If it doesn't exist, it is created with
297 * @gfp_flags and @node. The returned io_context has its reference count
300 * This function always goes through task_lock() and it's better to use
301 * %current->io_context + get_io_context() for %current.
303 struct io_context *get_task_io_context(struct task_struct *task,
304 gfp_t gfp_flags, int node)
306 struct io_context *ioc;
308 might_sleep_if(gfpflags_allow_blocking(gfp_flags));
312 ioc = task->io_context;
319 } while (!create_task_io_context(task, gfp_flags, node));
325 * ioc_lookup_icq - lookup io_cq from ioc
326 * @ioc: the associated io_context
327 * @q: the associated request_queue
329 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
330 * with @q->queue_lock held.
332 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
336 lockdep_assert_held(&q->queue_lock);
339 * icq's are indexed from @ioc using radix tree and hint pointer,
340 * both of which are protected with RCU. All removals are done
341 * holding both q and ioc locks, and we're holding q lock - if we
342 * find a icq which points to us, it's guaranteed to be valid.
345 icq = rcu_dereference(ioc->icq_hint);
346 if (icq && icq->q == q)
349 icq = radix_tree_lookup(&ioc->icq_tree, q->id);
350 if (icq && icq->q == q)
351 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
358 EXPORT_SYMBOL(ioc_lookup_icq);
361 * ioc_create_icq - create and link io_cq
362 * @ioc: io_context of interest
363 * @q: request_queue of interest
364 * @gfp_mask: allocation mask
366 * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
367 * will be created using @gfp_mask.
369 * The caller is responsible for ensuring @ioc won't go away and @q is
370 * alive and will stay alive until this function returns.
372 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
375 struct elevator_type *et = q->elevator->type;
379 icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
384 if (radix_tree_maybe_preload(gfp_mask) < 0) {
385 kmem_cache_free(et->icq_cache, icq);
391 INIT_LIST_HEAD(&icq->q_node);
392 INIT_HLIST_NODE(&icq->ioc_node);
394 /* lock both q and ioc and try to link @icq */
395 spin_lock_irq(&q->queue_lock);
396 spin_lock(&ioc->lock);
398 if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
399 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
400 list_add(&icq->q_node, &q->icq_list);
401 if (et->ops.init_icq)
402 et->ops.init_icq(icq);
404 kmem_cache_free(et->icq_cache, icq);
405 icq = ioc_lookup_icq(ioc, q);
407 printk(KERN_ERR "cfq: icq link failed!\n");
410 spin_unlock(&ioc->lock);
411 spin_unlock_irq(&q->queue_lock);
412 radix_tree_preload_end();
416 static int __init blk_ioc_init(void)
418 iocontext_cachep = kmem_cache_create("blkdev_ioc",
419 sizeof(struct io_context), 0, SLAB_PANIC, NULL);
422 subsys_initcall(blk_ioc_init);