1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* Watch queue and general notification mechanism, built on pipes |
3 | * |
4 | * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved. |
5 | * Written by David Howells (dhowells@redhat.com) |
6 | * |
7 | * See Documentation/core-api/watch_queue.rst |
8 | */ |
9 | |
10 | #define pr_fmt(fmt) "watchq: " fmt |
11 | #include <linux/module.h> |
12 | #include <linux/init.h> |
13 | #include <linux/sched.h> |
14 | #include <linux/slab.h> |
15 | #include <linux/printk.h> |
16 | #include <linux/miscdevice.h> |
17 | #include <linux/fs.h> |
18 | #include <linux/mm.h> |
19 | #include <linux/pagemap.h> |
20 | #include <linux/poll.h> |
21 | #include <linux/uaccess.h> |
22 | #include <linux/vmalloc.h> |
23 | #include <linux/file.h> |
24 | #include <linux/security.h> |
25 | #include <linux/cred.h> |
26 | #include <linux/sched/signal.h> |
27 | #include <linux/watch_queue.h> |
28 | #include <linux/pipe_fs_i.h> |
29 | |
30 | MODULE_DESCRIPTION("Watch queue" ); |
31 | MODULE_AUTHOR("Red Hat, Inc." ); |
32 | |
33 | #define WATCH_QUEUE_NOTE_SIZE 128 |
34 | #define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE) |
35 | |
36 | /* |
37 | * This must be called under the RCU read-lock, which makes |
38 | * sure that the wqueue still exists. It can then take the lock, |
39 | * and check that the wqueue hasn't been destroyed, which in |
40 | * turn makes sure that the notification pipe still exists. |
41 | */ |
42 | static inline bool lock_wqueue(struct watch_queue *wqueue) |
43 | { |
44 | spin_lock_bh(lock: &wqueue->lock); |
45 | if (unlikely(!wqueue->pipe)) { |
46 | spin_unlock_bh(lock: &wqueue->lock); |
47 | return false; |
48 | } |
49 | return true; |
50 | } |
51 | |
52 | static inline void unlock_wqueue(struct watch_queue *wqueue) |
53 | { |
54 | spin_unlock_bh(lock: &wqueue->lock); |
55 | } |
56 | |
57 | static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe, |
58 | struct pipe_buffer *buf) |
59 | { |
60 | struct watch_queue *wqueue = (struct watch_queue *)buf->private; |
61 | struct page *page; |
62 | unsigned int bit; |
63 | |
64 | /* We need to work out which note within the page this refers to, but |
65 | * the note might have been maximum size, so merely ANDing the offset |
66 | * off doesn't work. OTOH, the note must've been more than zero size. |
67 | */ |
68 | bit = buf->offset + buf->len; |
69 | if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0) |
70 | bit -= WATCH_QUEUE_NOTE_SIZE; |
71 | bit /= WATCH_QUEUE_NOTE_SIZE; |
72 | |
73 | page = buf->page; |
74 | bit += page->index; |
75 | |
76 | set_bit(nr: bit, addr: wqueue->notes_bitmap); |
77 | generic_pipe_buf_release(pipe, buf); |
78 | } |
79 | |
80 | // No try_steal function => no stealing |
81 | #define watch_queue_pipe_buf_try_steal NULL |
82 | |
83 | /* New data written to a pipe may be appended to a buffer with this type. */ |
84 | static const struct pipe_buf_operations watch_queue_pipe_buf_ops = { |
85 | .release = watch_queue_pipe_buf_release, |
86 | .try_steal = watch_queue_pipe_buf_try_steal, |
87 | .get = generic_pipe_buf_get, |
88 | }; |
89 | |
90 | /* |
91 | * Post a notification to a watch queue. |
92 | * |
93 | * Must be called with the RCU lock for reading, and the |
94 | * watch_queue lock held, which guarantees that the pipe |
95 | * hasn't been released. |
96 | */ |
97 | static bool post_one_notification(struct watch_queue *wqueue, |
98 | struct watch_notification *n) |
99 | { |
100 | void *p; |
101 | struct pipe_inode_info *pipe = wqueue->pipe; |
102 | struct pipe_buffer *buf; |
103 | struct page *page; |
104 | unsigned int head, tail, mask, note, offset, len; |
105 | bool done = false; |
106 | |
107 | spin_lock_irq(lock: &pipe->rd_wait.lock); |
108 | |
109 | mask = pipe->ring_size - 1; |
110 | head = pipe->head; |
111 | tail = pipe->tail; |
112 | if (pipe_full(head, tail, limit: pipe->ring_size)) |
113 | goto lost; |
114 | |
115 | note = find_first_bit(addr: wqueue->notes_bitmap, size: wqueue->nr_notes); |
116 | if (note >= wqueue->nr_notes) |
117 | goto lost; |
118 | |
119 | page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE]; |
120 | offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE; |
121 | get_page(page); |
122 | len = n->info & WATCH_INFO_LENGTH; |
123 | p = kmap_atomic(page); |
124 | memcpy(p + offset, n, len); |
125 | kunmap_atomic(p); |
126 | |
127 | buf = &pipe->bufs[head & mask]; |
128 | buf->page = page; |
129 | buf->private = (unsigned long)wqueue; |
130 | buf->ops = &watch_queue_pipe_buf_ops; |
131 | buf->offset = offset; |
132 | buf->len = len; |
133 | buf->flags = PIPE_BUF_FLAG_WHOLE; |
134 | smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */ |
135 | |
136 | if (!test_and_clear_bit(nr: note, addr: wqueue->notes_bitmap)) { |
137 | spin_unlock_irq(lock: &pipe->rd_wait.lock); |
138 | BUG(); |
139 | } |
140 | wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM); |
141 | done = true; |
142 | |
143 | out: |
144 | spin_unlock_irq(lock: &pipe->rd_wait.lock); |
145 | if (done) |
146 | kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); |
147 | return done; |
148 | |
149 | lost: |
150 | buf = &pipe->bufs[(head - 1) & mask]; |
151 | buf->flags |= PIPE_BUF_FLAG_LOSS; |
152 | goto out; |
153 | } |
154 | |
155 | /* |
156 | * Apply filter rules to a notification. |
157 | */ |
158 | static bool filter_watch_notification(const struct watch_filter *wf, |
159 | const struct watch_notification *n) |
160 | { |
161 | const struct watch_type_filter *wt; |
162 | unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8; |
163 | unsigned int st_index = n->subtype / st_bits; |
164 | unsigned int st_bit = 1U << (n->subtype % st_bits); |
165 | int i; |
166 | |
167 | if (!test_bit(n->type, wf->type_filter)) |
168 | return false; |
169 | |
170 | for (i = 0; i < wf->nr_filters; i++) { |
171 | wt = &wf->filters[i]; |
172 | if (n->type == wt->type && |
173 | (wt->subtype_filter[st_index] & st_bit) && |
174 | (n->info & wt->info_mask) == wt->info_filter) |
175 | return true; |
176 | } |
177 | |
178 | return false; /* If there is a filter, the default is to reject. */ |
179 | } |
180 | |
181 | /** |
182 | * __post_watch_notification - Post an event notification |
183 | * @wlist: The watch list to post the event to. |
184 | * @n: The notification record to post. |
185 | * @cred: The creds of the process that triggered the notification. |
186 | * @id: The ID to match on the watch. |
187 | * |
188 | * Post a notification of an event into a set of watch queues and let the users |
189 | * know. |
190 | * |
191 | * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and |
192 | * should be in units of sizeof(*n). |
193 | */ |
194 | void __post_watch_notification(struct watch_list *wlist, |
195 | struct watch_notification *n, |
196 | const struct cred *cred, |
197 | u64 id) |
198 | { |
199 | const struct watch_filter *wf; |
200 | struct watch_queue *wqueue; |
201 | struct watch *watch; |
202 | |
203 | if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) { |
204 | WARN_ON(1); |
205 | return; |
206 | } |
207 | |
208 | rcu_read_lock(); |
209 | |
210 | hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) { |
211 | if (watch->id != id) |
212 | continue; |
213 | n->info &= ~WATCH_INFO_ID; |
214 | n->info |= watch->info_id; |
215 | |
216 | wqueue = rcu_dereference(watch->queue); |
217 | wf = rcu_dereference(wqueue->filter); |
218 | if (wf && !filter_watch_notification(wf, n)) |
219 | continue; |
220 | |
221 | if (security_post_notification(w_cred: watch->cred, cred, n) < 0) |
222 | continue; |
223 | |
224 | if (lock_wqueue(wqueue)) { |
225 | post_one_notification(wqueue, n); |
226 | unlock_wqueue(wqueue); |
227 | } |
228 | } |
229 | |
230 | rcu_read_unlock(); |
231 | } |
232 | EXPORT_SYMBOL(__post_watch_notification); |
233 | |
234 | /* |
235 | * Allocate sufficient pages to preallocation for the requested number of |
236 | * notifications. |
237 | */ |
238 | long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) |
239 | { |
240 | struct watch_queue *wqueue = pipe->watch_queue; |
241 | struct page **pages; |
242 | unsigned long *bitmap; |
243 | unsigned long user_bufs; |
244 | int ret, i, nr_pages; |
245 | |
246 | if (!wqueue) |
247 | return -ENODEV; |
248 | if (wqueue->notes) |
249 | return -EBUSY; |
250 | |
251 | if (nr_notes < 1 || |
252 | nr_notes > 512) /* TODO: choose a better hard limit */ |
253 | return -EINVAL; |
254 | |
255 | nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1); |
256 | nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE; |
257 | user_bufs = account_pipe_buffers(user: pipe->user, old: pipe->nr_accounted, new: nr_pages); |
258 | |
259 | if (nr_pages > pipe->max_usage && |
260 | (too_many_pipe_buffers_hard(user_bufs) || |
261 | too_many_pipe_buffers_soft(user_bufs)) && |
262 | pipe_is_unprivileged_user()) { |
263 | ret = -EPERM; |
264 | goto error; |
265 | } |
266 | |
267 | nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE; |
268 | ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes)); |
269 | if (ret < 0) |
270 | goto error; |
271 | |
272 | ret = -ENOMEM; |
273 | pages = kcalloc(n: sizeof(struct page *), size: nr_pages, GFP_KERNEL); |
274 | if (!pages) |
275 | goto error; |
276 | |
277 | for (i = 0; i < nr_pages; i++) { |
278 | pages[i] = alloc_page(GFP_KERNEL); |
279 | if (!pages[i]) |
280 | goto error_p; |
281 | pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE; |
282 | } |
283 | |
284 | bitmap = bitmap_alloc(nbits: nr_notes, GFP_KERNEL); |
285 | if (!bitmap) |
286 | goto error_p; |
287 | |
288 | bitmap_fill(dst: bitmap, nbits: nr_notes); |
289 | wqueue->notes = pages; |
290 | wqueue->notes_bitmap = bitmap; |
291 | wqueue->nr_pages = nr_pages; |
292 | wqueue->nr_notes = nr_notes; |
293 | return 0; |
294 | |
295 | error_p: |
296 | while (--i >= 0) |
297 | __free_page(pages[i]); |
298 | kfree(objp: pages); |
299 | error: |
300 | (void) account_pipe_buffers(user: pipe->user, old: nr_pages, new: pipe->nr_accounted); |
301 | return ret; |
302 | } |
303 | |
304 | /* |
305 | * Set the filter on a watch queue. |
306 | */ |
307 | long watch_queue_set_filter(struct pipe_inode_info *pipe, |
308 | struct watch_notification_filter __user *_filter) |
309 | { |
310 | struct watch_notification_type_filter *tf; |
311 | struct watch_notification_filter filter; |
312 | struct watch_type_filter *q; |
313 | struct watch_filter *wfilter; |
314 | struct watch_queue *wqueue = pipe->watch_queue; |
315 | int ret, nr_filter = 0, i; |
316 | |
317 | if (!wqueue) |
318 | return -ENODEV; |
319 | |
320 | if (!_filter) { |
321 | /* Remove the old filter */ |
322 | wfilter = NULL; |
323 | goto set; |
324 | } |
325 | |
326 | /* Grab the user's filter specification */ |
327 | if (copy_from_user(to: &filter, from: _filter, n: sizeof(filter)) != 0) |
328 | return -EFAULT; |
329 | if (filter.nr_filters == 0 || |
330 | filter.nr_filters > 16 || |
331 | filter.__reserved != 0) |
332 | return -EINVAL; |
333 | |
334 | tf = memdup_array_user(src: _filter->filters, n: filter.nr_filters, size: sizeof(*tf)); |
335 | if (IS_ERR(ptr: tf)) |
336 | return PTR_ERR(ptr: tf); |
337 | |
338 | ret = -EINVAL; |
339 | for (i = 0; i < filter.nr_filters; i++) { |
340 | if ((tf[i].info_filter & ~tf[i].info_mask) || |
341 | tf[i].info_mask & WATCH_INFO_LENGTH) |
342 | goto err_filter; |
343 | /* Ignore any unknown types */ |
344 | if (tf[i].type >= WATCH_TYPE__NR) |
345 | continue; |
346 | nr_filter++; |
347 | } |
348 | |
349 | /* Now we need to build the internal filter from only the relevant |
350 | * user-specified filters. |
351 | */ |
352 | ret = -ENOMEM; |
353 | wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL); |
354 | if (!wfilter) |
355 | goto err_filter; |
356 | wfilter->nr_filters = nr_filter; |
357 | |
358 | q = wfilter->filters; |
359 | for (i = 0; i < filter.nr_filters; i++) { |
360 | if (tf[i].type >= WATCH_TYPE__NR) |
361 | continue; |
362 | |
363 | q->type = tf[i].type; |
364 | q->info_filter = tf[i].info_filter; |
365 | q->info_mask = tf[i].info_mask; |
366 | q->subtype_filter[0] = tf[i].subtype_filter[0]; |
367 | __set_bit(q->type, wfilter->type_filter); |
368 | q++; |
369 | } |
370 | |
371 | kfree(objp: tf); |
372 | set: |
373 | pipe_lock(pipe); |
374 | wfilter = rcu_replace_pointer(wqueue->filter, wfilter, |
375 | lockdep_is_held(&pipe->mutex)); |
376 | pipe_unlock(pipe); |
377 | if (wfilter) |
378 | kfree_rcu(wfilter, rcu); |
379 | return 0; |
380 | |
381 | err_filter: |
382 | kfree(objp: tf); |
383 | return ret; |
384 | } |
385 | |
386 | static void __put_watch_queue(struct kref *kref) |
387 | { |
388 | struct watch_queue *wqueue = |
389 | container_of(kref, struct watch_queue, usage); |
390 | struct watch_filter *wfilter; |
391 | int i; |
392 | |
393 | for (i = 0; i < wqueue->nr_pages; i++) |
394 | __free_page(wqueue->notes[i]); |
395 | kfree(objp: wqueue->notes); |
396 | bitmap_free(bitmap: wqueue->notes_bitmap); |
397 | |
398 | wfilter = rcu_access_pointer(wqueue->filter); |
399 | if (wfilter) |
400 | kfree_rcu(wfilter, rcu); |
401 | kfree_rcu(wqueue, rcu); |
402 | } |
403 | |
404 | /** |
405 | * put_watch_queue - Dispose of a ref on a watchqueue. |
406 | * @wqueue: The watch queue to unref. |
407 | */ |
408 | void put_watch_queue(struct watch_queue *wqueue) |
409 | { |
410 | kref_put(kref: &wqueue->usage, release: __put_watch_queue); |
411 | } |
412 | EXPORT_SYMBOL(put_watch_queue); |
413 | |
414 | static void free_watch(struct rcu_head *rcu) |
415 | { |
416 | struct watch *watch = container_of(rcu, struct watch, rcu); |
417 | |
418 | put_watch_queue(rcu_access_pointer(watch->queue)); |
419 | atomic_dec(v: &watch->cred->user->nr_watches); |
420 | put_cred(cred: watch->cred); |
421 | kfree(objp: watch); |
422 | } |
423 | |
424 | static void __put_watch(struct kref *kref) |
425 | { |
426 | struct watch *watch = container_of(kref, struct watch, usage); |
427 | |
428 | call_rcu(head: &watch->rcu, func: free_watch); |
429 | } |
430 | |
431 | /* |
432 | * Discard a watch. |
433 | */ |
434 | static void put_watch(struct watch *watch) |
435 | { |
436 | kref_put(kref: &watch->usage, release: __put_watch); |
437 | } |
438 | |
439 | /** |
440 | * init_watch - Initialise a watch |
441 | * @watch: The watch to initialise. |
442 | * @wqueue: The queue to assign. |
443 | * |
444 | * Initialise a watch and set the watch queue. |
445 | */ |
446 | void init_watch(struct watch *watch, struct watch_queue *wqueue) |
447 | { |
448 | kref_init(kref: &watch->usage); |
449 | INIT_HLIST_NODE(h: &watch->list_node); |
450 | INIT_HLIST_NODE(h: &watch->queue_node); |
451 | rcu_assign_pointer(watch->queue, wqueue); |
452 | } |
453 | |
454 | static int add_one_watch(struct watch *watch, struct watch_list *wlist, struct watch_queue *wqueue) |
455 | { |
456 | const struct cred *cred; |
457 | struct watch *w; |
458 | |
459 | hlist_for_each_entry(w, &wlist->watchers, list_node) { |
460 | struct watch_queue *wq = rcu_access_pointer(w->queue); |
461 | if (wqueue == wq && watch->id == w->id) |
462 | return -EBUSY; |
463 | } |
464 | |
465 | cred = current_cred(); |
466 | if (atomic_inc_return(v: &cred->user->nr_watches) > task_rlimit(current, RLIMIT_NOFILE)) { |
467 | atomic_dec(v: &cred->user->nr_watches); |
468 | return -EAGAIN; |
469 | } |
470 | |
471 | watch->cred = get_cred(cred); |
472 | rcu_assign_pointer(watch->watch_list, wlist); |
473 | |
474 | kref_get(kref: &wqueue->usage); |
475 | kref_get(kref: &watch->usage); |
476 | hlist_add_head(n: &watch->queue_node, h: &wqueue->watches); |
477 | hlist_add_head_rcu(n: &watch->list_node, h: &wlist->watchers); |
478 | return 0; |
479 | } |
480 | |
481 | /** |
482 | * add_watch_to_object - Add a watch on an object to a watch list |
483 | * @watch: The watch to add |
484 | * @wlist: The watch list to add to |
485 | * |
486 | * @watch->queue must have been set to point to the queue to post notifications |
487 | * to and the watch list of the object to be watched. @watch->cred must also |
488 | * have been set to the appropriate credentials and a ref taken on them. |
489 | * |
490 | * The caller must pin the queue and the list both and must hold the list |
491 | * locked against racing watch additions/removals. |
492 | */ |
493 | int add_watch_to_object(struct watch *watch, struct watch_list *wlist) |
494 | { |
495 | struct watch_queue *wqueue; |
496 | int ret = -ENOENT; |
497 | |
498 | rcu_read_lock(); |
499 | |
500 | wqueue = rcu_access_pointer(watch->queue); |
501 | if (lock_wqueue(wqueue)) { |
502 | spin_lock(lock: &wlist->lock); |
503 | ret = add_one_watch(watch, wlist, wqueue); |
504 | spin_unlock(lock: &wlist->lock); |
505 | unlock_wqueue(wqueue); |
506 | } |
507 | |
508 | rcu_read_unlock(); |
509 | return ret; |
510 | } |
511 | EXPORT_SYMBOL(add_watch_to_object); |
512 | |
513 | /** |
514 | * remove_watch_from_object - Remove a watch or all watches from an object. |
515 | * @wlist: The watch list to remove from |
516 | * @wq: The watch queue of interest (ignored if @all is true) |
517 | * @id: The ID of the watch to remove (ignored if @all is true) |
518 | * @all: True to remove all objects |
519 | * |
520 | * Remove a specific watch or all watches from an object. A notification is |
521 | * sent to the watcher to tell them that this happened. |
522 | */ |
523 | int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq, |
524 | u64 id, bool all) |
525 | { |
526 | struct watch_notification_removal n; |
527 | struct watch_queue *wqueue; |
528 | struct watch *watch; |
529 | int ret = -EBADSLT; |
530 | |
531 | rcu_read_lock(); |
532 | |
533 | again: |
534 | spin_lock(lock: &wlist->lock); |
535 | hlist_for_each_entry(watch, &wlist->watchers, list_node) { |
536 | if (all || |
537 | (watch->id == id && rcu_access_pointer(watch->queue) == wq)) |
538 | goto found; |
539 | } |
540 | spin_unlock(lock: &wlist->lock); |
541 | goto out; |
542 | |
543 | found: |
544 | ret = 0; |
545 | hlist_del_init_rcu(n: &watch->list_node); |
546 | rcu_assign_pointer(watch->watch_list, NULL); |
547 | spin_unlock(lock: &wlist->lock); |
548 | |
549 | /* We now own the reference on watch that used to belong to wlist. */ |
550 | |
551 | n.watch.type = WATCH_TYPE_META; |
552 | n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION; |
553 | n.watch.info = watch->info_id | watch_sizeof(n.watch); |
554 | n.id = id; |
555 | if (id != 0) |
556 | n.watch.info = watch->info_id | watch_sizeof(n); |
557 | |
558 | wqueue = rcu_dereference(watch->queue); |
559 | |
560 | if (lock_wqueue(wqueue)) { |
561 | post_one_notification(wqueue, n: &n.watch); |
562 | |
563 | if (!hlist_unhashed(h: &watch->queue_node)) { |
564 | hlist_del_init_rcu(n: &watch->queue_node); |
565 | put_watch(watch); |
566 | } |
567 | |
568 | unlock_wqueue(wqueue); |
569 | } |
570 | |
571 | if (wlist->release_watch) { |
572 | void (*release_watch)(struct watch *); |
573 | |
574 | release_watch = wlist->release_watch; |
575 | rcu_read_unlock(); |
576 | (*release_watch)(watch); |
577 | rcu_read_lock(); |
578 | } |
579 | put_watch(watch); |
580 | |
581 | if (all && !hlist_empty(h: &wlist->watchers)) |
582 | goto again; |
583 | out: |
584 | rcu_read_unlock(); |
585 | return ret; |
586 | } |
587 | EXPORT_SYMBOL(remove_watch_from_object); |
588 | |
589 | /* |
590 | * Remove all the watches that are contributory to a queue. This has the |
591 | * potential to race with removal of the watches by the destruction of the |
592 | * objects being watched or with the distribution of notifications. |
593 | */ |
594 | void watch_queue_clear(struct watch_queue *wqueue) |
595 | { |
596 | struct watch_list *wlist; |
597 | struct watch *watch; |
598 | bool release; |
599 | |
600 | rcu_read_lock(); |
601 | spin_lock_bh(lock: &wqueue->lock); |
602 | |
603 | /* |
604 | * This pipe can be freed by callers like free_pipe_info(). |
605 | * Removing this reference also prevents new notifications. |
606 | */ |
607 | wqueue->pipe = NULL; |
608 | |
609 | while (!hlist_empty(h: &wqueue->watches)) { |
610 | watch = hlist_entry(wqueue->watches.first, struct watch, queue_node); |
611 | hlist_del_init_rcu(n: &watch->queue_node); |
612 | /* We now own a ref on the watch. */ |
613 | spin_unlock_bh(lock: &wqueue->lock); |
614 | |
615 | /* We can't do the next bit under the queue lock as we need to |
616 | * get the list lock - which would cause a deadlock if someone |
617 | * was removing from the opposite direction at the same time or |
618 | * posting a notification. |
619 | */ |
620 | wlist = rcu_dereference(watch->watch_list); |
621 | if (wlist) { |
622 | void (*release_watch)(struct watch *); |
623 | |
624 | spin_lock(lock: &wlist->lock); |
625 | |
626 | release = !hlist_unhashed(h: &watch->list_node); |
627 | if (release) { |
628 | hlist_del_init_rcu(n: &watch->list_node); |
629 | rcu_assign_pointer(watch->watch_list, NULL); |
630 | |
631 | /* We now own a second ref on the watch. */ |
632 | } |
633 | |
634 | release_watch = wlist->release_watch; |
635 | spin_unlock(lock: &wlist->lock); |
636 | |
637 | if (release) { |
638 | if (release_watch) { |
639 | rcu_read_unlock(); |
640 | /* This might need to call dput(), so |
641 | * we have to drop all the locks. |
642 | */ |
643 | (*release_watch)(watch); |
644 | rcu_read_lock(); |
645 | } |
646 | put_watch(watch); |
647 | } |
648 | } |
649 | |
650 | put_watch(watch); |
651 | spin_lock_bh(lock: &wqueue->lock); |
652 | } |
653 | |
654 | spin_unlock_bh(lock: &wqueue->lock); |
655 | rcu_read_unlock(); |
656 | } |
657 | |
658 | /** |
659 | * get_watch_queue - Get a watch queue from its file descriptor. |
660 | * @fd: The fd to query. |
661 | */ |
662 | struct watch_queue *get_watch_queue(int fd) |
663 | { |
664 | struct pipe_inode_info *pipe; |
665 | struct watch_queue *wqueue = ERR_PTR(error: -EINVAL); |
666 | struct fd f; |
667 | |
668 | f = fdget(fd); |
669 | if (f.file) { |
670 | pipe = get_pipe_info(file: f.file, for_splice: false); |
671 | if (pipe && pipe->watch_queue) { |
672 | wqueue = pipe->watch_queue; |
673 | kref_get(kref: &wqueue->usage); |
674 | } |
675 | fdput(fd: f); |
676 | } |
677 | |
678 | return wqueue; |
679 | } |
680 | EXPORT_SYMBOL(get_watch_queue); |
681 | |
682 | /* |
683 | * Initialise a watch queue |
684 | */ |
685 | int watch_queue_init(struct pipe_inode_info *pipe) |
686 | { |
687 | struct watch_queue *wqueue; |
688 | |
689 | wqueue = kzalloc(size: sizeof(*wqueue), GFP_KERNEL); |
690 | if (!wqueue) |
691 | return -ENOMEM; |
692 | |
693 | wqueue->pipe = pipe; |
694 | kref_init(kref: &wqueue->usage); |
695 | spin_lock_init(&wqueue->lock); |
696 | INIT_HLIST_HEAD(&wqueue->watches); |
697 | |
698 | pipe->watch_queue = wqueue; |
699 | return 0; |
700 | } |
701 | |