f53c80ecaf076c69367b371a334c15bc76473d10
[deliverable/linux.git] / 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 */
17 static 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 */
25 void get_io_context(struct io_context *ioc)
26 {
27 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
28 atomic_long_inc(&ioc->refcount);
29 }
30 EXPORT_SYMBOL(get_io_context);
31
32 static 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 /*
40 * Exit and free an icq. Called with both ioc and q locked.
41 */
42 static void ioc_exit_icq(struct io_cq *icq)
43 {
44 struct io_context *ioc = icq->ioc;
45 struct request_queue *q = icq->q;
46 struct elevator_type *et = q->elevator->type;
47
48 lockdep_assert_held(&ioc->lock);
49 lockdep_assert_held(q->queue_lock);
50
51 radix_tree_delete(&ioc->icq_tree, icq->q->id);
52 hlist_del_init(&icq->ioc_node);
53 list_del_init(&icq->q_node);
54
55 /*
56 * Both setting lookup hint to and clearing it from @icq are done
57 * under queue_lock. If it's not pointing to @icq now, it never
58 * will. Hint assignment itself can race safely.
59 */
60 if (rcu_dereference_raw(ioc->icq_hint) == icq)
61 rcu_assign_pointer(ioc->icq_hint, NULL);
62
63 if (et->ops.elevator_exit_icq_fn)
64 et->ops.elevator_exit_icq_fn(icq);
65
66 /*
67 * @icq->q might have gone away by the time RCU callback runs
68 * making it impossible to determine icq_cache. Record it in @icq.
69 */
70 icq->__rcu_icq_cache = et->icq_cache;
71 call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
72 }
73
74 /*
75 * Slow path for ioc release in put_io_context(). Performs double-lock
76 * dancing to unlink all icq's and then frees ioc.
77 */
78 static void ioc_release_fn(struct work_struct *work)
79 {
80 struct io_context *ioc = container_of(work, struct io_context,
81 release_work);
82 unsigned long flags;
83
84 /*
85 * Exiting icq may call into put_io_context() through elevator
86 * which will trigger lockdep warning. The ioc's are guaranteed to
87 * be different, use a different locking subclass here. Use
88 * irqsave variant as there's no spin_lock_irq_nested().
89 */
90 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
91
92 while (!hlist_empty(&ioc->icq_list)) {
93 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
94 struct io_cq, ioc_node);
95 struct request_queue *q = icq->q;
96
97 if (spin_trylock(q->queue_lock)) {
98 ioc_exit_icq(icq);
99 spin_unlock(q->queue_lock);
100 } else {
101 spin_unlock_irqrestore(&ioc->lock, flags);
102 cpu_relax();
103 spin_lock_irqsave_nested(&ioc->lock, flags, 1);
104 }
105 }
106
107 spin_unlock_irqrestore(&ioc->lock, flags);
108
109 kmem_cache_free(iocontext_cachep, ioc);
110 }
111
112 /**
113 * put_io_context - put a reference of io_context
114 * @ioc: io_context to put
115 *
116 * Decrement reference count of @ioc and release it if the count reaches
117 * zero.
118 */
119 void put_io_context(struct io_context *ioc)
120 {
121 unsigned long flags;
122
123 if (ioc == NULL)
124 return;
125
126 BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
127
128 /*
129 * Releasing ioc requires reverse order double locking and we may
130 * already be holding a queue_lock. Do it asynchronously from wq.
131 */
132 if (atomic_long_dec_and_test(&ioc->refcount)) {
133 spin_lock_irqsave(&ioc->lock, flags);
134 if (!hlist_empty(&ioc->icq_list))
135 schedule_work(&ioc->release_work);
136 spin_unlock_irqrestore(&ioc->lock, flags);
137 }
138 }
139 EXPORT_SYMBOL(put_io_context);
140
141 /* Called by the exiting task */
142 void exit_io_context(struct task_struct *task)
143 {
144 struct io_context *ioc;
145
146 task_lock(task);
147 ioc = task->io_context;
148 task->io_context = NULL;
149 task_unlock(task);
150
151 atomic_dec(&ioc->nr_tasks);
152 put_io_context(ioc);
153 }
154
155 /**
156 * ioc_clear_queue - break any ioc association with the specified queue
157 * @q: request_queue being cleared
158 *
159 * Walk @q->icq_list and exit all io_cq's. Must be called with @q locked.
160 */
161 void ioc_clear_queue(struct request_queue *q)
162 {
163 lockdep_assert_held(q->queue_lock);
164
165 while (!list_empty(&q->icq_list)) {
166 struct io_cq *icq = list_entry(q->icq_list.next,
167 struct io_cq, q_node);
168 struct io_context *ioc = icq->ioc;
169
170 spin_lock(&ioc->lock);
171 ioc_exit_icq(icq);
172 spin_unlock(&ioc->lock);
173 }
174 }
175
176 void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_flags,
177 int node)
178 {
179 struct io_context *ioc;
180
181 ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
182 node);
183 if (unlikely(!ioc))
184 return;
185
186 /* initialize */
187 atomic_long_set(&ioc->refcount, 1);
188 atomic_set(&ioc->nr_tasks, 1);
189 spin_lock_init(&ioc->lock);
190 INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
191 INIT_HLIST_HEAD(&ioc->icq_list);
192 INIT_WORK(&ioc->release_work, ioc_release_fn);
193
194 /*
195 * Try to install. ioc shouldn't be installed if someone else
196 * already did or @task, which isn't %current, is exiting. Note
197 * that we need to allow ioc creation on exiting %current as exit
198 * path may issue IOs from e.g. exit_files(). The exit path is
199 * responsible for not issuing IO after exit_io_context().
200 */
201 task_lock(task);
202 if (!task->io_context &&
203 (task == current || !(task->flags & PF_EXITING)))
204 task->io_context = ioc;
205 else
206 kmem_cache_free(iocontext_cachep, ioc);
207 task_unlock(task);
208 }
209
210 /**
211 * get_task_io_context - get io_context of a task
212 * @task: task of interest
213 * @gfp_flags: allocation flags, used if allocation is necessary
214 * @node: allocation node, used if allocation is necessary
215 *
216 * Return io_context of @task. If it doesn't exist, it is created with
217 * @gfp_flags and @node. The returned io_context has its reference count
218 * incremented.
219 *
220 * This function always goes through task_lock() and it's better to use
221 * %current->io_context + get_io_context() for %current.
222 */
223 struct io_context *get_task_io_context(struct task_struct *task,
224 gfp_t gfp_flags, int node)
225 {
226 struct io_context *ioc;
227
228 might_sleep_if(gfp_flags & __GFP_WAIT);
229
230 do {
231 task_lock(task);
232 ioc = task->io_context;
233 if (likely(ioc)) {
234 get_io_context(ioc);
235 task_unlock(task);
236 return ioc;
237 }
238 task_unlock(task);
239 } while (create_io_context(task, gfp_flags, node));
240
241 return NULL;
242 }
243 EXPORT_SYMBOL(get_task_io_context);
244
245 /**
246 * ioc_lookup_icq - lookup io_cq from ioc
247 * @ioc: the associated io_context
248 * @q: the associated request_queue
249 *
250 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
251 * with @q->queue_lock held.
252 */
253 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
254 {
255 struct io_cq *icq;
256
257 lockdep_assert_held(q->queue_lock);
258
259 /*
260 * icq's are indexed from @ioc using radix tree and hint pointer,
261 * both of which are protected with RCU. All removals are done
262 * holding both q and ioc locks, and we're holding q lock - if we
263 * find a icq which points to us, it's guaranteed to be valid.
264 */
265 rcu_read_lock();
266 icq = rcu_dereference(ioc->icq_hint);
267 if (icq && icq->q == q)
268 goto out;
269
270 icq = radix_tree_lookup(&ioc->icq_tree, q->id);
271 if (icq && icq->q == q)
272 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
273 else
274 icq = NULL;
275 out:
276 rcu_read_unlock();
277 return icq;
278 }
279 EXPORT_SYMBOL(ioc_lookup_icq);
280
281 /**
282 * ioc_create_icq - create and link io_cq
283 * @q: request_queue of interest
284 * @gfp_mask: allocation mask
285 *
286 * Make sure io_cq linking %current->io_context and @q exists. If either
287 * io_context and/or icq don't exist, they will be created using @gfp_mask.
288 *
289 * The caller is responsible for ensuring @ioc won't go away and @q is
290 * alive and will stay alive until this function returns.
291 */
292 struct io_cq *ioc_create_icq(struct request_queue *q, gfp_t gfp_mask)
293 {
294 struct elevator_type *et = q->elevator->type;
295 struct io_context *ioc;
296 struct io_cq *icq;
297
298 /* allocate stuff */
299 ioc = create_io_context(current, gfp_mask, q->node);
300 if (!ioc)
301 return NULL;
302
303 icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
304 q->node);
305 if (!icq)
306 return NULL;
307
308 if (radix_tree_preload(gfp_mask) < 0) {
309 kmem_cache_free(et->icq_cache, icq);
310 return NULL;
311 }
312
313 icq->ioc = ioc;
314 icq->q = q;
315 INIT_LIST_HEAD(&icq->q_node);
316 INIT_HLIST_NODE(&icq->ioc_node);
317
318 /* lock both q and ioc and try to link @icq */
319 spin_lock_irq(q->queue_lock);
320 spin_lock(&ioc->lock);
321
322 if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
323 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
324 list_add(&icq->q_node, &q->icq_list);
325 if (et->ops.elevator_init_icq_fn)
326 et->ops.elevator_init_icq_fn(icq);
327 } else {
328 kmem_cache_free(et->icq_cache, icq);
329 icq = ioc_lookup_icq(ioc, q);
330 if (!icq)
331 printk(KERN_ERR "cfq: icq link failed!\n");
332 }
333
334 spin_unlock(&ioc->lock);
335 spin_unlock_irq(q->queue_lock);
336 radix_tree_preload_end();
337 return icq;
338 }
339
340 void ioc_set_icq_flags(struct io_context *ioc, unsigned int flags)
341 {
342 struct io_cq *icq;
343 struct hlist_node *n;
344
345 hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node)
346 icq->flags |= flags;
347 }
348
349 /**
350 * ioc_ioprio_changed - notify ioprio change
351 * @ioc: io_context of interest
352 * @ioprio: new ioprio
353 *
354 * @ioc's ioprio has changed to @ioprio. Set %ICQ_IOPRIO_CHANGED for all
355 * icq's. iosched is responsible for checking the bit and applying it on
356 * request issue path.
357 */
358 void ioc_ioprio_changed(struct io_context *ioc, int ioprio)
359 {
360 unsigned long flags;
361
362 spin_lock_irqsave(&ioc->lock, flags);
363 ioc->ioprio = ioprio;
364 ioc_set_icq_flags(ioc, ICQ_IOPRIO_CHANGED);
365 spin_unlock_irqrestore(&ioc->lock, flags);
366 }
367
368 /**
369 * ioc_cgroup_changed - notify cgroup change
370 * @ioc: io_context of interest
371 *
372 * @ioc's cgroup has changed. Set %ICQ_CGROUP_CHANGED for all icq's.
373 * iosched is responsible for checking the bit and applying it on request
374 * issue path.
375 */
376 void ioc_cgroup_changed(struct io_context *ioc)
377 {
378 unsigned long flags;
379
380 spin_lock_irqsave(&ioc->lock, flags);
381 ioc_set_icq_flags(ioc, ICQ_CGROUP_CHANGED);
382 spin_unlock_irqrestore(&ioc->lock, flags);
383 }
384 EXPORT_SYMBOL(ioc_cgroup_changed);
385
386 /**
387 * icq_get_changed - fetch and clear icq changed mask
388 * @icq: icq of interest
389 *
390 * Fetch and clear ICQ_*_CHANGED bits from @icq. Grabs and releases
391 * @icq->ioc->lock.
392 */
393 unsigned icq_get_changed(struct io_cq *icq)
394 {
395 unsigned int changed = 0;
396 unsigned long flags;
397
398 if (unlikely(icq->flags & ICQ_CHANGED_MASK)) {
399 spin_lock_irqsave(&icq->ioc->lock, flags);
400 changed = icq->flags & ICQ_CHANGED_MASK;
401 icq->flags &= ~ICQ_CHANGED_MASK;
402 spin_unlock_irqrestore(&icq->ioc->lock, flags);
403 }
404 return changed;
405 }
406 EXPORT_SYMBOL(icq_get_changed);
407
408 static int __init blk_ioc_init(void)
409 {
410 iocontext_cachep = kmem_cache_create("blkdev_ioc",
411 sizeof(struct io_context), 0, SLAB_PANIC, NULL);
412 return 0;
413 }
414 subsys_initcall(blk_ioc_init);
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