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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/slab.h> |
10 | |
11 | #include "blk.h" |
12 | |
13 | /* |
14 | * For io context allocations |
15 | */ |
16 | static struct kmem_cache *iocontext_cachep; |
17 | |
18 | /** |
19 | * get_io_context - increment reference count to io_context |
20 | * @ioc: io_context to get |
21 | * |
22 | * Increment reference count to @ioc. |
23 | */ |
24 | void get_io_context(struct io_context *ioc) |
25 | { |
26 | BUG_ON(atomic_long_read(&ioc->refcount) <= 0); |
27 | atomic_long_inc(&ioc->refcount); |
28 | } |
29 | EXPORT_SYMBOL(get_io_context); |
30 | |
31 | static void icq_free_icq_rcu(struct rcu_head *head) |
32 | { |
33 | struct io_cq *icq = container_of(head, struct io_cq, __rcu_head); |
34 | |
35 | kmem_cache_free(icq->__rcu_icq_cache, icq); |
36 | } |
37 | |
38 | /* Exit an icq. Called with both ioc and q locked. */ |
39 | static void ioc_exit_icq(struct io_cq *icq) |
40 | { |
41 | struct elevator_type *et = icq->q->elevator->type; |
42 | |
43 | if (icq->flags & ICQ_EXITED) |
44 | return; |
45 | |
46 | if (et->ops.elevator_exit_icq_fn) |
47 | et->ops.elevator_exit_icq_fn(icq); |
48 | |
49 | icq->flags |= ICQ_EXITED; |
50 | } |
51 | |
52 | /* Release an icq. Called with both ioc and q locked. */ |
53 | static void ioc_destroy_icq(struct io_cq *icq) |
54 | { |
55 | struct io_context *ioc = icq->ioc; |
56 | struct request_queue *q = icq->q; |
57 | struct elevator_type *et = q->elevator->type; |
58 | |
59 | lockdep_assert_held(&ioc->lock); |
60 | lockdep_assert_held(q->queue_lock); |
61 | |
62 | radix_tree_delete(&ioc->icq_tree, icq->q->id); |
63 | hlist_del_init(&icq->ioc_node); |
64 | list_del_init(&icq->q_node); |
65 | |
66 | /* |
67 | * Both setting lookup hint to and clearing it from @icq are done |
68 | * under queue_lock. If it's not pointing to @icq now, it never |
69 | * will. Hint assignment itself can race safely. |
70 | */ |
71 | if (rcu_access_pointer(ioc->icq_hint) == icq) |
72 | rcu_assign_pointer(ioc->icq_hint, NULL); |
73 | |
74 | ioc_exit_icq(icq); |
75 | |
76 | /* |
77 | * @icq->q might have gone away by the time RCU callback runs |
78 | * making it impossible to determine icq_cache. Record it in @icq. |
79 | */ |
80 | icq->__rcu_icq_cache = et->icq_cache; |
81 | call_rcu(&icq->__rcu_head, icq_free_icq_rcu); |
82 | } |
83 | |
84 | /* |
85 | * Slow path for ioc release in put_io_context(). Performs double-lock |
86 | * dancing to unlink all icq's and then frees ioc. |
87 | */ |
88 | static void ioc_release_fn(struct work_struct *work) |
89 | { |
90 | struct io_context *ioc = container_of(work, struct io_context, |
91 | release_work); |
92 | unsigned long flags; |
93 | |
94 | /* |
95 | * Exiting icq may call into put_io_context() through elevator |
96 | * which will trigger lockdep warning. The ioc's are guaranteed to |
97 | * be different, use a different locking subclass here. Use |
98 | * irqsave variant as there's no spin_lock_irq_nested(). |
99 | */ |
100 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); |
101 | |
102 | while (!hlist_empty(&ioc->icq_list)) { |
103 | struct io_cq *icq = hlist_entry(ioc->icq_list.first, |
104 | struct io_cq, ioc_node); |
105 | struct request_queue *q = icq->q; |
106 | |
107 | if (spin_trylock(q->queue_lock)) { |
108 | ioc_destroy_icq(icq); |
109 | spin_unlock(q->queue_lock); |
110 | } else { |
111 | spin_unlock_irqrestore(&ioc->lock, flags); |
112 | cpu_relax(); |
113 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); |
114 | } |
115 | } |
116 | |
117 | spin_unlock_irqrestore(&ioc->lock, flags); |
118 | |
119 | kmem_cache_free(iocontext_cachep, ioc); |
120 | } |
121 | |
122 | /** |
123 | * put_io_context - put a reference of io_context |
124 | * @ioc: io_context to put |
125 | * |
126 | * Decrement reference count of @ioc and release it if the count reaches |
127 | * zero. |
128 | */ |
129 | void put_io_context(struct io_context *ioc) |
130 | { |
131 | unsigned long flags; |
132 | bool free_ioc = false; |
133 | |
134 | if (ioc == NULL) |
135 | return; |
136 | |
137 | BUG_ON(atomic_long_read(&ioc->refcount) <= 0); |
138 | |
139 | /* |
140 | * Releasing ioc requires reverse order double locking and we may |
141 | * already be holding a queue_lock. Do it asynchronously from wq. |
142 | */ |
143 | if (atomic_long_dec_and_test(&ioc->refcount)) { |
144 | spin_lock_irqsave(&ioc->lock, flags); |
145 | if (!hlist_empty(&ioc->icq_list)) |
146 | queue_work(system_power_efficient_wq, |
147 | &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 | } |
156 | EXPORT_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 | */ |
165 | void 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 | */ |
180 | retry: |
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 */ |
200 | void 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 | */ |
219 | void 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 | |
234 | int 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 | */ |
287 | struct 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 | } |
307 | EXPORT_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 | */ |
317 | struct 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; |
339 | out: |
340 | rcu_read_unlock(); |
341 | return icq; |
342 | } |
343 | EXPORT_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 | */ |
357 | struct 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_maybe_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 | |
401 | static 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 | } |
407 | subsys_initcall(blk_ioc_init); |
408 |
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