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c73be61c DH |
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/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 | MODULE_LICENSE("GPL"); | |
33 | ||
34 | #define WATCH_QUEUE_NOTE_SIZE 128 | |
35 | #define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE) | |
36 | ||
37 | static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe, | |
38 | struct pipe_buffer *buf) | |
39 | { | |
40 | struct watch_queue *wqueue = (struct watch_queue *)buf->private; | |
41 | struct page *page; | |
42 | unsigned int bit; | |
43 | ||
44 | /* We need to work out which note within the page this refers to, but | |
45 | * the note might have been maximum size, so merely ANDing the offset | |
46 | * off doesn't work. OTOH, the note must've been more than zero size. | |
47 | */ | |
48 | bit = buf->offset + buf->len; | |
49 | if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0) | |
50 | bit -= WATCH_QUEUE_NOTE_SIZE; | |
51 | bit /= WATCH_QUEUE_NOTE_SIZE; | |
52 | ||
53 | page = buf->page; | |
54 | bit += page->index; | |
55 | ||
56 | set_bit(bit, wqueue->notes_bitmap); | |
c1853fba | 57 | generic_pipe_buf_release(pipe, buf); |
c73be61c DH |
58 | } |
59 | ||
6c329784 LT |
60 | // No try_steal function => no stealing |
61 | #define watch_queue_pipe_buf_try_steal NULL | |
c73be61c DH |
62 | |
63 | /* New data written to a pipe may be appended to a buffer with this type. */ | |
64 | static const struct pipe_buf_operations watch_queue_pipe_buf_ops = { | |
c73be61c | 65 | .release = watch_queue_pipe_buf_release, |
6c329784 | 66 | .try_steal = watch_queue_pipe_buf_try_steal, |
c73be61c DH |
67 | .get = generic_pipe_buf_get, |
68 | }; | |
69 | ||
70 | /* | |
71 | * Post a notification to a watch queue. | |
72 | */ | |
73 | static bool post_one_notification(struct watch_queue *wqueue, | |
74 | struct watch_notification *n) | |
75 | { | |
76 | void *p; | |
77 | struct pipe_inode_info *pipe = wqueue->pipe; | |
78 | struct pipe_buffer *buf; | |
79 | struct page *page; | |
80 | unsigned int head, tail, mask, note, offset, len; | |
81 | bool done = false; | |
82 | ||
83 | if (!pipe) | |
84 | return false; | |
85 | ||
86 | spin_lock_irq(&pipe->rd_wait.lock); | |
87 | ||
88 | if (wqueue->defunct) | |
89 | goto out; | |
90 | ||
91 | mask = pipe->ring_size - 1; | |
92 | head = pipe->head; | |
93 | tail = pipe->tail; | |
94 | if (pipe_full(head, tail, pipe->ring_size)) | |
95 | goto lost; | |
96 | ||
97 | note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes); | |
98 | if (note >= wqueue->nr_notes) | |
99 | goto lost; | |
100 | ||
101 | page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE]; | |
102 | offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE; | |
103 | get_page(page); | |
104 | len = n->info & WATCH_INFO_LENGTH; | |
105 | p = kmap_atomic(page); | |
106 | memcpy(p + offset, n, len); | |
107 | kunmap_atomic(p); | |
108 | ||
109 | buf = &pipe->bufs[head & mask]; | |
110 | buf->page = page; | |
111 | buf->private = (unsigned long)wqueue; | |
112 | buf->ops = &watch_queue_pipe_buf_ops; | |
113 | buf->offset = offset; | |
114 | buf->len = len; | |
8cfba763 | 115 | buf->flags = PIPE_BUF_FLAG_WHOLE; |
2ed147f0 | 116 | smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */ |
c73be61c DH |
117 | |
118 | if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { | |
119 | spin_unlock_irq(&pipe->rd_wait.lock); | |
120 | BUG(); | |
121 | } | |
122 | wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM); | |
123 | done = true; | |
124 | ||
125 | out: | |
126 | spin_unlock_irq(&pipe->rd_wait.lock); | |
127 | if (done) | |
128 | kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); | |
129 | return done; | |
130 | ||
131 | lost: | |
e7d553d6 DH |
132 | buf = &pipe->bufs[(head - 1) & mask]; |
133 | buf->flags |= PIPE_BUF_FLAG_LOSS; | |
c73be61c DH |
134 | goto out; |
135 | } | |
136 | ||
137 | /* | |
138 | * Apply filter rules to a notification. | |
139 | */ | |
140 | static bool filter_watch_notification(const struct watch_filter *wf, | |
141 | const struct watch_notification *n) | |
142 | { | |
143 | const struct watch_type_filter *wt; | |
144 | unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8; | |
145 | unsigned int st_index = n->subtype / st_bits; | |
146 | unsigned int st_bit = 1U << (n->subtype % st_bits); | |
147 | int i; | |
148 | ||
149 | if (!test_bit(n->type, wf->type_filter)) | |
150 | return false; | |
151 | ||
152 | for (i = 0; i < wf->nr_filters; i++) { | |
153 | wt = &wf->filters[i]; | |
154 | if (n->type == wt->type && | |
155 | (wt->subtype_filter[st_index] & st_bit) && | |
156 | (n->info & wt->info_mask) == wt->info_filter) | |
157 | return true; | |
158 | } | |
159 | ||
160 | return false; /* If there is a filter, the default is to reject. */ | |
161 | } | |
162 | ||
163 | /** | |
164 | * __post_watch_notification - Post an event notification | |
165 | * @wlist: The watch list to post the event to. | |
166 | * @n: The notification record to post. | |
167 | * @cred: The creds of the process that triggered the notification. | |
168 | * @id: The ID to match on the watch. | |
169 | * | |
170 | * Post a notification of an event into a set of watch queues and let the users | |
171 | * know. | |
172 | * | |
173 | * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and | |
174 | * should be in units of sizeof(*n). | |
175 | */ | |
176 | void __post_watch_notification(struct watch_list *wlist, | |
177 | struct watch_notification *n, | |
178 | const struct cred *cred, | |
179 | u64 id) | |
180 | { | |
181 | const struct watch_filter *wf; | |
182 | struct watch_queue *wqueue; | |
183 | struct watch *watch; | |
184 | ||
185 | if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) { | |
186 | WARN_ON(1); | |
187 | return; | |
188 | } | |
189 | ||
190 | rcu_read_lock(); | |
191 | ||
192 | hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) { | |
193 | if (watch->id != id) | |
194 | continue; | |
195 | n->info &= ~WATCH_INFO_ID; | |
196 | n->info |= watch->info_id; | |
197 | ||
198 | wqueue = rcu_dereference(watch->queue); | |
199 | wf = rcu_dereference(wqueue->filter); | |
200 | if (wf && !filter_watch_notification(wf, n)) | |
201 | continue; | |
202 | ||
203 | if (security_post_notification(watch->cred, cred, n) < 0) | |
204 | continue; | |
205 | ||
206 | post_one_notification(wqueue, n); | |
207 | } | |
208 | ||
209 | rcu_read_unlock(); | |
210 | } | |
211 | EXPORT_SYMBOL(__post_watch_notification); | |
212 | ||
213 | /* | |
214 | * Allocate sufficient pages to preallocation for the requested number of | |
215 | * notifications. | |
216 | */ | |
217 | long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) | |
218 | { | |
219 | struct watch_queue *wqueue = pipe->watch_queue; | |
220 | struct page **pages; | |
221 | unsigned long *bitmap; | |
222 | unsigned long user_bufs; | |
c73be61c DH |
223 | int ret, i, nr_pages; |
224 | ||
225 | if (!wqueue) | |
226 | return -ENODEV; | |
227 | if (wqueue->notes) | |
228 | return -EBUSY; | |
229 | ||
230 | if (nr_notes < 1 || | |
231 | nr_notes > 512) /* TODO: choose a better hard limit */ | |
232 | return -EINVAL; | |
233 | ||
234 | nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1); | |
235 | nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE; | |
236 | user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages); | |
237 | ||
238 | if (nr_pages > pipe->max_usage && | |
239 | (too_many_pipe_buffers_hard(user_bufs) || | |
240 | too_many_pipe_buffers_soft(user_bufs)) && | |
241 | pipe_is_unprivileged_user()) { | |
242 | ret = -EPERM; | |
243 | goto error; | |
244 | } | |
245 | ||
3b4c0371 | 246 | nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE; |
96a4d891 | 247 | ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes)); |
c73be61c DH |
248 | if (ret < 0) |
249 | goto error; | |
250 | ||
251 | pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL); | |
252 | if (!pages) | |
253 | goto error; | |
254 | ||
255 | for (i = 0; i < nr_pages; i++) { | |
256 | pages[i] = alloc_page(GFP_KERNEL); | |
257 | if (!pages[i]) | |
258 | goto error_p; | |
259 | pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE; | |
260 | } | |
261 | ||
a66bd757 | 262 | bitmap = bitmap_alloc(nr_notes, GFP_KERNEL); |
c73be61c DH |
263 | if (!bitmap) |
264 | goto error_p; | |
265 | ||
a66bd757 | 266 | bitmap_fill(bitmap, nr_notes); |
c73be61c DH |
267 | wqueue->notes = pages; |
268 | wqueue->notes_bitmap = bitmap; | |
269 | wqueue->nr_pages = nr_pages; | |
3b4c0371 | 270 | wqueue->nr_notes = nr_notes; |
c73be61c DH |
271 | return 0; |
272 | ||
273 | error_p: | |
a635415a | 274 | while (--i >= 0) |
c73be61c DH |
275 | __free_page(pages[i]); |
276 | kfree(pages); | |
277 | error: | |
278 | (void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted); | |
279 | return ret; | |
280 | } | |
281 | ||
282 | /* | |
283 | * Set the filter on a watch queue. | |
284 | */ | |
285 | long watch_queue_set_filter(struct pipe_inode_info *pipe, | |
286 | struct watch_notification_filter __user *_filter) | |
287 | { | |
288 | struct watch_notification_type_filter *tf; | |
289 | struct watch_notification_filter filter; | |
290 | struct watch_type_filter *q; | |
291 | struct watch_filter *wfilter; | |
292 | struct watch_queue *wqueue = pipe->watch_queue; | |
293 | int ret, nr_filter = 0, i; | |
294 | ||
295 | if (!wqueue) | |
296 | return -ENODEV; | |
297 | ||
298 | if (!_filter) { | |
299 | /* Remove the old filter */ | |
300 | wfilter = NULL; | |
301 | goto set; | |
302 | } | |
303 | ||
304 | /* Grab the user's filter specification */ | |
305 | if (copy_from_user(&filter, _filter, sizeof(filter)) != 0) | |
306 | return -EFAULT; | |
307 | if (filter.nr_filters == 0 || | |
308 | filter.nr_filters > 16 || | |
309 | filter.__reserved != 0) | |
310 | return -EINVAL; | |
311 | ||
312 | tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf)); | |
313 | if (IS_ERR(tf)) | |
314 | return PTR_ERR(tf); | |
315 | ||
316 | ret = -EINVAL; | |
317 | for (i = 0; i < filter.nr_filters; i++) { | |
318 | if ((tf[i].info_filter & ~tf[i].info_mask) || | |
319 | tf[i].info_mask & WATCH_INFO_LENGTH) | |
320 | goto err_filter; | |
321 | /* Ignore any unknown types */ | |
c993ee0f | 322 | if (tf[i].type >= WATCH_TYPE__NR) |
c73be61c DH |
323 | continue; |
324 | nr_filter++; | |
325 | } | |
326 | ||
327 | /* Now we need to build the internal filter from only the relevant | |
328 | * user-specified filters. | |
329 | */ | |
330 | ret = -ENOMEM; | |
331 | wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL); | |
332 | if (!wfilter) | |
333 | goto err_filter; | |
334 | wfilter->nr_filters = nr_filter; | |
335 | ||
336 | q = wfilter->filters; | |
337 | for (i = 0; i < filter.nr_filters; i++) { | |
c993ee0f | 338 | if (tf[i].type >= WATCH_TYPE__NR) |
c73be61c DH |
339 | continue; |
340 | ||
341 | q->type = tf[i].type; | |
342 | q->info_filter = tf[i].info_filter; | |
343 | q->info_mask = tf[i].info_mask; | |
344 | q->subtype_filter[0] = tf[i].subtype_filter[0]; | |
345 | __set_bit(q->type, wfilter->type_filter); | |
346 | q++; | |
347 | } | |
348 | ||
349 | kfree(tf); | |
350 | set: | |
351 | pipe_lock(pipe); | |
352 | wfilter = rcu_replace_pointer(wqueue->filter, wfilter, | |
353 | lockdep_is_held(&pipe->mutex)); | |
354 | pipe_unlock(pipe); | |
355 | if (wfilter) | |
356 | kfree_rcu(wfilter, rcu); | |
357 | return 0; | |
358 | ||
359 | err_filter: | |
360 | kfree(tf); | |
361 | return ret; | |
362 | } | |
363 | ||
364 | static void __put_watch_queue(struct kref *kref) | |
365 | { | |
366 | struct watch_queue *wqueue = | |
367 | container_of(kref, struct watch_queue, usage); | |
368 | struct watch_filter *wfilter; | |
369 | int i; | |
370 | ||
371 | for (i = 0; i < wqueue->nr_pages; i++) | |
372 | __free_page(wqueue->notes[i]); | |
b4902070 | 373 | kfree(wqueue->notes); |
7ea1a012 | 374 | bitmap_free(wqueue->notes_bitmap); |
c73be61c DH |
375 | |
376 | wfilter = rcu_access_pointer(wqueue->filter); | |
377 | if (wfilter) | |
378 | kfree_rcu(wfilter, rcu); | |
379 | kfree_rcu(wqueue, rcu); | |
380 | } | |
381 | ||
382 | /** | |
383 | * put_watch_queue - Dispose of a ref on a watchqueue. | |
384 | * @wqueue: The watch queue to unref. | |
385 | */ | |
386 | void put_watch_queue(struct watch_queue *wqueue) | |
387 | { | |
388 | kref_put(&wqueue->usage, __put_watch_queue); | |
389 | } | |
390 | EXPORT_SYMBOL(put_watch_queue); | |
391 | ||
392 | static void free_watch(struct rcu_head *rcu) | |
393 | { | |
394 | struct watch *watch = container_of(rcu, struct watch, rcu); | |
395 | ||
396 | put_watch_queue(rcu_access_pointer(watch->queue)); | |
29e44f45 | 397 | atomic_dec(&watch->cred->user->nr_watches); |
c73be61c | 398 | put_cred(watch->cred); |
3d8dcf27 | 399 | kfree(watch); |
c73be61c DH |
400 | } |
401 | ||
402 | static void __put_watch(struct kref *kref) | |
403 | { | |
404 | struct watch *watch = container_of(kref, struct watch, usage); | |
405 | ||
406 | call_rcu(&watch->rcu, free_watch); | |
407 | } | |
408 | ||
409 | /* | |
410 | * Discard a watch. | |
411 | */ | |
412 | static void put_watch(struct watch *watch) | |
413 | { | |
414 | kref_put(&watch->usage, __put_watch); | |
415 | } | |
416 | ||
417 | /** | |
8f0bfc25 | 418 | * init_watch - Initialise a watch |
c73be61c DH |
419 | * @watch: The watch to initialise. |
420 | * @wqueue: The queue to assign. | |
421 | * | |
422 | * Initialise a watch and set the watch queue. | |
423 | */ | |
424 | void init_watch(struct watch *watch, struct watch_queue *wqueue) | |
425 | { | |
426 | kref_init(&watch->usage); | |
427 | INIT_HLIST_NODE(&watch->list_node); | |
428 | INIT_HLIST_NODE(&watch->queue_node); | |
429 | rcu_assign_pointer(watch->queue, wqueue); | |
430 | } | |
431 | ||
432 | /** | |
433 | * add_watch_to_object - Add a watch on an object to a watch list | |
434 | * @watch: The watch to add | |
435 | * @wlist: The watch list to add to | |
436 | * | |
437 | * @watch->queue must have been set to point to the queue to post notifications | |
438 | * to and the watch list of the object to be watched. @watch->cred must also | |
439 | * have been set to the appropriate credentials and a ref taken on them. | |
440 | * | |
441 | * The caller must pin the queue and the list both and must hold the list | |
442 | * locked against racing watch additions/removals. | |
443 | */ | |
444 | int add_watch_to_object(struct watch *watch, struct watch_list *wlist) | |
445 | { | |
446 | struct watch_queue *wqueue = rcu_access_pointer(watch->queue); | |
447 | struct watch *w; | |
448 | ||
449 | hlist_for_each_entry(w, &wlist->watchers, list_node) { | |
450 | struct watch_queue *wq = rcu_access_pointer(w->queue); | |
451 | if (wqueue == wq && watch->id == w->id) | |
452 | return -EBUSY; | |
453 | } | |
454 | ||
455 | watch->cred = get_current_cred(); | |
456 | rcu_assign_pointer(watch->watch_list, wlist); | |
457 | ||
29e44f45 DH |
458 | if (atomic_inc_return(&watch->cred->user->nr_watches) > |
459 | task_rlimit(current, RLIMIT_NOFILE)) { | |
460 | atomic_dec(&watch->cred->user->nr_watches); | |
461 | put_cred(watch->cred); | |
462 | return -EAGAIN; | |
463 | } | |
464 | ||
c73be61c DH |
465 | spin_lock_bh(&wqueue->lock); |
466 | kref_get(&wqueue->usage); | |
467 | kref_get(&watch->usage); | |
468 | hlist_add_head(&watch->queue_node, &wqueue->watches); | |
469 | spin_unlock_bh(&wqueue->lock); | |
470 | ||
471 | hlist_add_head(&watch->list_node, &wlist->watchers); | |
472 | return 0; | |
473 | } | |
474 | EXPORT_SYMBOL(add_watch_to_object); | |
475 | ||
476 | /** | |
477 | * remove_watch_from_object - Remove a watch or all watches from an object. | |
478 | * @wlist: The watch list to remove from | |
479 | * @wq: The watch queue of interest (ignored if @all is true) | |
480 | * @id: The ID of the watch to remove (ignored if @all is true) | |
481 | * @all: True to remove all objects | |
482 | * | |
483 | * Remove a specific watch or all watches from an object. A notification is | |
484 | * sent to the watcher to tell them that this happened. | |
485 | */ | |
486 | int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq, | |
487 | u64 id, bool all) | |
488 | { | |
489 | struct watch_notification_removal n; | |
490 | struct watch_queue *wqueue; | |
491 | struct watch *watch; | |
492 | int ret = -EBADSLT; | |
493 | ||
494 | rcu_read_lock(); | |
495 | ||
496 | again: | |
497 | spin_lock(&wlist->lock); | |
498 | hlist_for_each_entry(watch, &wlist->watchers, list_node) { | |
499 | if (all || | |
500 | (watch->id == id && rcu_access_pointer(watch->queue) == wq)) | |
501 | goto found; | |
502 | } | |
503 | spin_unlock(&wlist->lock); | |
504 | goto out; | |
505 | ||
506 | found: | |
507 | ret = 0; | |
508 | hlist_del_init_rcu(&watch->list_node); | |
509 | rcu_assign_pointer(watch->watch_list, NULL); | |
510 | spin_unlock(&wlist->lock); | |
511 | ||
512 | /* We now own the reference on watch that used to belong to wlist. */ | |
513 | ||
514 | n.watch.type = WATCH_TYPE_META; | |
515 | n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION; | |
516 | n.watch.info = watch->info_id | watch_sizeof(n.watch); | |
517 | n.id = id; | |
518 | if (id != 0) | |
519 | n.watch.info = watch->info_id | watch_sizeof(n); | |
520 | ||
521 | wqueue = rcu_dereference(watch->queue); | |
522 | ||
523 | /* We don't need the watch list lock for the next bit as RCU is | |
524 | * protecting *wqueue from deallocation. | |
525 | */ | |
526 | if (wqueue) { | |
527 | post_one_notification(wqueue, &n.watch); | |
528 | ||
529 | spin_lock_bh(&wqueue->lock); | |
530 | ||
531 | if (!hlist_unhashed(&watch->queue_node)) { | |
532 | hlist_del_init_rcu(&watch->queue_node); | |
533 | put_watch(watch); | |
534 | } | |
535 | ||
536 | spin_unlock_bh(&wqueue->lock); | |
537 | } | |
538 | ||
539 | if (wlist->release_watch) { | |
540 | void (*release_watch)(struct watch *); | |
541 | ||
542 | release_watch = wlist->release_watch; | |
543 | rcu_read_unlock(); | |
544 | (*release_watch)(watch); | |
545 | rcu_read_lock(); | |
546 | } | |
547 | put_watch(watch); | |
548 | ||
549 | if (all && !hlist_empty(&wlist->watchers)) | |
550 | goto again; | |
551 | out: | |
552 | rcu_read_unlock(); | |
553 | return ret; | |
554 | } | |
555 | EXPORT_SYMBOL(remove_watch_from_object); | |
556 | ||
557 | /* | |
558 | * Remove all the watches that are contributory to a queue. This has the | |
559 | * potential to race with removal of the watches by the destruction of the | |
560 | * objects being watched or with the distribution of notifications. | |
561 | */ | |
562 | void watch_queue_clear(struct watch_queue *wqueue) | |
563 | { | |
564 | struct watch_list *wlist; | |
565 | struct watch *watch; | |
566 | bool release; | |
567 | ||
568 | rcu_read_lock(); | |
569 | spin_lock_bh(&wqueue->lock); | |
570 | ||
4edc0760 | 571 | /* Prevent new notifications from being stored. */ |
c73be61c DH |
572 | wqueue->defunct = true; |
573 | ||
574 | while (!hlist_empty(&wqueue->watches)) { | |
575 | watch = hlist_entry(wqueue->watches.first, struct watch, queue_node); | |
576 | hlist_del_init_rcu(&watch->queue_node); | |
577 | /* We now own a ref on the watch. */ | |
578 | spin_unlock_bh(&wqueue->lock); | |
579 | ||
580 | /* We can't do the next bit under the queue lock as we need to | |
581 | * get the list lock - which would cause a deadlock if someone | |
582 | * was removing from the opposite direction at the same time or | |
583 | * posting a notification. | |
584 | */ | |
585 | wlist = rcu_dereference(watch->watch_list); | |
586 | if (wlist) { | |
587 | void (*release_watch)(struct watch *); | |
588 | ||
589 | spin_lock(&wlist->lock); | |
590 | ||
591 | release = !hlist_unhashed(&watch->list_node); | |
592 | if (release) { | |
593 | hlist_del_init_rcu(&watch->list_node); | |
594 | rcu_assign_pointer(watch->watch_list, NULL); | |
595 | ||
596 | /* We now own a second ref on the watch. */ | |
597 | } | |
598 | ||
599 | release_watch = wlist->release_watch; | |
600 | spin_unlock(&wlist->lock); | |
601 | ||
602 | if (release) { | |
603 | if (release_watch) { | |
604 | rcu_read_unlock(); | |
605 | /* This might need to call dput(), so | |
606 | * we have to drop all the locks. | |
607 | */ | |
608 | (*release_watch)(watch); | |
609 | rcu_read_lock(); | |
610 | } | |
611 | put_watch(watch); | |
612 | } | |
613 | } | |
614 | ||
615 | put_watch(watch); | |
616 | spin_lock_bh(&wqueue->lock); | |
617 | } | |
618 | ||
619 | spin_unlock_bh(&wqueue->lock); | |
620 | rcu_read_unlock(); | |
621 | } | |
622 | ||
623 | /** | |
624 | * get_watch_queue - Get a watch queue from its file descriptor. | |
625 | * @fd: The fd to query. | |
626 | */ | |
627 | struct watch_queue *get_watch_queue(int fd) | |
628 | { | |
629 | struct pipe_inode_info *pipe; | |
630 | struct watch_queue *wqueue = ERR_PTR(-EINVAL); | |
631 | struct fd f; | |
632 | ||
633 | f = fdget(fd); | |
634 | if (f.file) { | |
635 | pipe = get_pipe_info(f.file, false); | |
636 | if (pipe && pipe->watch_queue) { | |
637 | wqueue = pipe->watch_queue; | |
638 | kref_get(&wqueue->usage); | |
639 | } | |
640 | fdput(f); | |
641 | } | |
642 | ||
643 | return wqueue; | |
644 | } | |
645 | EXPORT_SYMBOL(get_watch_queue); | |
646 | ||
647 | /* | |
648 | * Initialise a watch queue | |
649 | */ | |
650 | int watch_queue_init(struct pipe_inode_info *pipe) | |
651 | { | |
652 | struct watch_queue *wqueue; | |
653 | ||
654 | wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL); | |
655 | if (!wqueue) | |
656 | return -ENOMEM; | |
657 | ||
658 | wqueue->pipe = pipe; | |
659 | kref_init(&wqueue->usage); | |
660 | spin_lock_init(&wqueue->lock); | |
661 | INIT_HLIST_HEAD(&wqueue->watches); | |
662 | ||
663 | pipe->watch_queue = wqueue; | |
664 | return 0; | |
665 | } |