2 * Functions related to io context handling
4 #include <linux/kernel.h>
5 #include <linux/module.h>
6 #include <linux/init.h>
8 #include <linux/blkdev.h>
9 #include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
10 #include <linux/slab.h>
15 * For io context allocations
17 static struct kmem_cache *iocontext_cachep;
20 * get_io_context - increment reference count to io_context
21 * @ioc: io_context to get
23 * Increment reference count to @ioc.
25 void get_io_context(struct io_context *ioc)
27 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
28 atomic_long_inc(&ioc->refcount);
30 EXPORT_SYMBOL(get_io_context);
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);
39 /* Exit an icq. Called with both ioc and q locked. */
40 static void ioc_exit_icq(struct io_cq *icq)
42 struct elevator_type *et = icq->q->elevator->type;
44 if (icq->flags & ICQ_EXITED)
47 if (et->ops.elevator_exit_icq_fn)
48 et->ops.elevator_exit_icq_fn(icq);
50 icq->flags |= ICQ_EXITED;
53 /* Release an icq. Called with both ioc and q locked. */
54 static void ioc_destroy_icq(struct io_cq *icq)
56 struct io_context *ioc = icq->ioc;
57 struct request_queue *q = icq->q;
58 struct elevator_type *et = q->elevator->type;
60 lockdep_assert_held(&ioc->lock);
61 lockdep_assert_held(q->queue_lock);
63 radix_tree_delete(&ioc->icq_tree, icq->q->id);
64 hlist_del_init(&icq->ioc_node);
65 list_del_init(&icq->q_node);
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.
72 if (rcu_dereference_raw(ioc->icq_hint) == icq)
73 rcu_assign_pointer(ioc->icq_hint, NULL);
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.
81 icq->__rcu_icq_cache = et->icq_cache;
82 call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
86 * Slow path for ioc release in put_io_context(). Performs double-lock
87 * dancing to unlink all icq's and then frees ioc.
89 static void ioc_release_fn(struct work_struct *work)
91 struct io_context *ioc = container_of(work, struct io_context,
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().
101 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
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;
108 if (spin_trylock(q->queue_lock)) {
109 ioc_destroy_icq(icq);
110 spin_unlock(q->queue_lock);
112 spin_unlock_irqrestore(&ioc->lock, flags);
114 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
118 spin_unlock_irqrestore(&ioc->lock, flags);
120 kmem_cache_free(iocontext_cachep, ioc);
124 * put_io_context - put a reference of io_context
125 * @ioc: io_context to put
127 * Decrement reference count of @ioc and release it if the count reaches
130 void put_io_context(struct io_context *ioc)
133 bool free_ioc = false;
138 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
141 * Releasing ioc requires reverse order double locking and we may
142 * already be holding a queue_lock. Do it asynchronously from wq.
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);
150 spin_unlock_irqrestore(&ioc->lock, flags);
154 kmem_cache_free(iocontext_cachep, ioc);
156 EXPORT_SYMBOL(put_io_context);
159 * put_io_context_active - put active reference on ioc
160 * @ioc: ioc of interest
162 * Undo get_io_context_active(). If active reference reaches zero after
163 * put, @ioc can never issue further IOs and ioscheds are notified.
165 void put_io_context_active(struct io_context *ioc)
167 struct hlist_node *n;
171 if (!atomic_dec_and_test(&ioc->active_ref)) {
177 * Need ioc lock to walk icq_list and q lock to exit icq. Perform
178 * reverse double locking. Read comment in ioc_release_fn() for
179 * explanation on the nested locking annotation.
182 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
183 hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node) {
184 if (icq->flags & ICQ_EXITED)
186 if (spin_trylock(icq->q->queue_lock)) {
188 spin_unlock(icq->q->queue_lock);
190 spin_unlock_irqrestore(&ioc->lock, flags);
195 spin_unlock_irqrestore(&ioc->lock, flags);
200 /* Called by the exiting task */
201 void exit_io_context(struct task_struct *task)
203 struct io_context *ioc;
206 ioc = task->io_context;
207 task->io_context = NULL;
210 atomic_dec(&ioc->nr_tasks);
211 put_io_context_active(ioc);
215 * ioc_clear_queue - break any ioc association with the specified queue
216 * @q: request_queue being cleared
218 * Walk @q->icq_list and exit all io_cq's. Must be called with @q locked.
220 void ioc_clear_queue(struct request_queue *q)
222 lockdep_assert_held(q->queue_lock);
224 while (!list_empty(&q->icq_list)) {
225 struct io_cq *icq = list_entry(q->icq_list.next,
226 struct io_cq, q_node);
227 struct io_context *ioc = icq->ioc;
229 spin_lock(&ioc->lock);
230 ioc_destroy_icq(icq);
231 spin_unlock(&ioc->lock);
235 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
237 struct io_context *ioc;
240 ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
246 atomic_long_set(&ioc->refcount, 1);
247 atomic_set(&ioc->nr_tasks, 1);
248 atomic_set(&ioc->active_ref, 1);
249 spin_lock_init(&ioc->lock);
250 INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
251 INIT_HLIST_HEAD(&ioc->icq_list);
252 INIT_WORK(&ioc->release_work, ioc_release_fn);
255 * Try to install. ioc shouldn't be installed if someone else
256 * already did or @task, which isn't %current, is exiting. Note
257 * that we need to allow ioc creation on exiting %current as exit
258 * path may issue IOs from e.g. exit_files(). The exit path is
259 * responsible for not issuing IO after exit_io_context().
262 if (!task->io_context &&
263 (task == current || !(task->flags & PF_EXITING)))
264 task->io_context = ioc;
266 kmem_cache_free(iocontext_cachep, ioc);
268 ret = task->io_context ? 0 : -EBUSY;
276 * get_task_io_context - get io_context of a task
277 * @task: task of interest
278 * @gfp_flags: allocation flags, used if allocation is necessary
279 * @node: allocation node, used if allocation is necessary
281 * Return io_context of @task. If it doesn't exist, it is created with
282 * @gfp_flags and @node. The returned io_context has its reference count
285 * This function always goes through task_lock() and it's better to use
286 * %current->io_context + get_io_context() for %current.
288 struct io_context *get_task_io_context(struct task_struct *task,
289 gfp_t gfp_flags, int node)
291 struct io_context *ioc;
293 might_sleep_if(gfp_flags & __GFP_WAIT);
297 ioc = task->io_context;
304 } while (!create_task_io_context(task, gfp_flags, node));
308 EXPORT_SYMBOL(get_task_io_context);
311 * ioc_lookup_icq - lookup io_cq from ioc
312 * @ioc: the associated io_context
313 * @q: the associated request_queue
315 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
316 * with @q->queue_lock held.
318 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
322 lockdep_assert_held(q->queue_lock);
325 * icq's are indexed from @ioc using radix tree and hint pointer,
326 * both of which are protected with RCU. All removals are done
327 * holding both q and ioc locks, and we're holding q lock - if we
328 * find a icq which points to us, it's guaranteed to be valid.
331 icq = rcu_dereference(ioc->icq_hint);
332 if (icq && icq->q == q)
335 icq = radix_tree_lookup(&ioc->icq_tree, q->id);
336 if (icq && icq->q == q)
337 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
344 EXPORT_SYMBOL(ioc_lookup_icq);
347 * ioc_create_icq - create and link io_cq
348 * @ioc: io_context of interest
349 * @q: request_queue of interest
350 * @gfp_mask: allocation mask
352 * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
353 * will be created using @gfp_mask.
355 * The caller is responsible for ensuring @ioc won't go away and @q is
356 * alive and will stay alive until this function returns.
358 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
361 struct elevator_type *et = q->elevator->type;
365 icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
370 if (radix_tree_preload(gfp_mask) < 0) {
371 kmem_cache_free(et->icq_cache, icq);
377 INIT_LIST_HEAD(&icq->q_node);
378 INIT_HLIST_NODE(&icq->ioc_node);
380 /* lock both q and ioc and try to link @icq */
381 spin_lock_irq(q->queue_lock);
382 spin_lock(&ioc->lock);
384 if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
385 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
386 list_add(&icq->q_node, &q->icq_list);
387 if (et->ops.elevator_init_icq_fn)
388 et->ops.elevator_init_icq_fn(icq);
390 kmem_cache_free(et->icq_cache, icq);
391 icq = ioc_lookup_icq(ioc, q);
393 printk(KERN_ERR "cfq: icq link failed!\n");
396 spin_unlock(&ioc->lock);
397 spin_unlock_irq(q->queue_lock);
398 radix_tree_preload_end();
402 static int __init blk_ioc_init(void)
404 iocontext_cachep = kmem_cache_create("blkdev_ioc",
405 sizeof(struct io_context), 0, SLAB_PANIC, NULL);
408 subsys_initcall(blk_ioc_init);