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 /*
38 * This must be called under the RCU read-lock, which makes
39 * sure that the wqueue still exists. It can then take the lock,
40 * and check that the wqueue hasn't been destroyed, which in
41 * turn makes sure that the notification pipe still exists.
42 */
lock_wqueue(struct watch_queue * wqueue)43 static inline bool lock_wqueue(struct watch_queue *wqueue)
44 {
45 spin_lock_bh(&wqueue->lock);
46 if (unlikely(wqueue->defunct)) {
47 spin_unlock_bh(&wqueue->lock);
48 return false;
49 }
50 return true;
51 }
52
unlock_wqueue(struct watch_queue * wqueue)53 static inline void unlock_wqueue(struct watch_queue *wqueue)
54 {
55 spin_unlock_bh(&wqueue->lock);
56 }
57
watch_queue_pipe_buf_release(struct pipe_inode_info * pipe,struct pipe_buffer * buf)58 static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe,
59 struct pipe_buffer *buf)
60 {
61 struct watch_queue *wqueue = (struct watch_queue *)buf->private;
62 struct page *page;
63 unsigned int bit;
64
65 /* We need to work out which note within the page this refers to, but
66 * the note might have been maximum size, so merely ANDing the offset
67 * off doesn't work. OTOH, the note must've been more than zero size.
68 */
69 bit = buf->offset + buf->len;
70 if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0)
71 bit -= WATCH_QUEUE_NOTE_SIZE;
72 bit /= WATCH_QUEUE_NOTE_SIZE;
73
74 page = buf->page;
75 bit += page->index;
76
77 set_bit(bit, wqueue->notes_bitmap);
78 generic_pipe_buf_release(pipe, buf);
79 }
80
81 // No try_steal function => no stealing
82 #define watch_queue_pipe_buf_try_steal NULL
83
84 /* New data written to a pipe may be appended to a buffer with this type. */
85 static const struct pipe_buf_operations watch_queue_pipe_buf_ops = {
86 .release = watch_queue_pipe_buf_release,
87 .try_steal = watch_queue_pipe_buf_try_steal,
88 .get = generic_pipe_buf_get,
89 };
90
91 /*
92 * Post a notification to a watch queue.
93 *
94 * Must be called with the RCU lock for reading, and the
95 * watch_queue lock held, which guarantees that the pipe
96 * hasn't been released.
97 */
post_one_notification(struct watch_queue * wqueue,struct watch_notification * n)98 static bool post_one_notification(struct watch_queue *wqueue,
99 struct watch_notification *n)
100 {
101 void *p;
102 struct pipe_inode_info *pipe = wqueue->pipe;
103 struct pipe_buffer *buf;
104 struct page *page;
105 unsigned int head, tail, mask, note, offset, len;
106 bool done = false;
107
108 if (!pipe)
109 return false;
110
111 spin_lock_irq(&pipe->rd_wait.lock);
112
113 mask = pipe->ring_size - 1;
114 head = pipe->head;
115 tail = pipe->tail;
116 if (pipe_full(head, tail, pipe->ring_size))
117 goto lost;
118
119 note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
120 if (note >= wqueue->nr_notes)
121 goto lost;
122
123 page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE];
124 offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE;
125 get_page(page);
126 len = n->info & WATCH_INFO_LENGTH;
127 p = kmap_atomic(page);
128 memcpy(p + offset, n, len);
129 kunmap_atomic(p);
130
131 buf = &pipe->bufs[head & mask];
132 buf->page = page;
133 buf->private = (unsigned long)wqueue;
134 buf->ops = &watch_queue_pipe_buf_ops;
135 buf->offset = offset;
136 buf->len = len;
137 buf->flags = PIPE_BUF_FLAG_WHOLE;
138 smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */
139
140 if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {
141 spin_unlock_irq(&pipe->rd_wait.lock);
142 BUG();
143 }
144 wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
145 done = true;
146
147 out:
148 spin_unlock_irq(&pipe->rd_wait.lock);
149 if (done)
150 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
151 return done;
152
153 lost:
154 buf = &pipe->bufs[(head - 1) & mask];
155 buf->flags |= PIPE_BUF_FLAG_LOSS;
156 goto out;
157 }
158
159 /*
160 * Apply filter rules to a notification.
161 */
filter_watch_notification(const struct watch_filter * wf,const struct watch_notification * n)162 static bool filter_watch_notification(const struct watch_filter *wf,
163 const struct watch_notification *n)
164 {
165 const struct watch_type_filter *wt;
166 unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8;
167 unsigned int st_index = n->subtype / st_bits;
168 unsigned int st_bit = 1U << (n->subtype % st_bits);
169 int i;
170
171 if (!test_bit(n->type, wf->type_filter))
172 return false;
173
174 for (i = 0; i < wf->nr_filters; i++) {
175 wt = &wf->filters[i];
176 if (n->type == wt->type &&
177 (wt->subtype_filter[st_index] & st_bit) &&
178 (n->info & wt->info_mask) == wt->info_filter)
179 return true;
180 }
181
182 return false; /* If there is a filter, the default is to reject. */
183 }
184
185 /**
186 * __post_watch_notification - Post an event notification
187 * @wlist: The watch list to post the event to.
188 * @n: The notification record to post.
189 * @cred: The creds of the process that triggered the notification.
190 * @id: The ID to match on the watch.
191 *
192 * Post a notification of an event into a set of watch queues and let the users
193 * know.
194 *
195 * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and
196 * should be in units of sizeof(*n).
197 */
__post_watch_notification(struct watch_list * wlist,struct watch_notification * n,const struct cred * cred,u64 id)198 void __post_watch_notification(struct watch_list *wlist,
199 struct watch_notification *n,
200 const struct cred *cred,
201 u64 id)
202 {
203 const struct watch_filter *wf;
204 struct watch_queue *wqueue;
205 struct watch *watch;
206
207 if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) {
208 WARN_ON(1);
209 return;
210 }
211
212 rcu_read_lock();
213
214 hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) {
215 if (watch->id != id)
216 continue;
217 n->info &= ~WATCH_INFO_ID;
218 n->info |= watch->info_id;
219
220 wqueue = rcu_dereference(watch->queue);
221 wf = rcu_dereference(wqueue->filter);
222 if (wf && !filter_watch_notification(wf, n))
223 continue;
224
225 if (security_post_notification(watch->cred, cred, n) < 0)
226 continue;
227
228 if (lock_wqueue(wqueue)) {
229 post_one_notification(wqueue, n);
230 unlock_wqueue(wqueue);
231 }
232 }
233
234 rcu_read_unlock();
235 }
236 EXPORT_SYMBOL(__post_watch_notification);
237
238 /*
239 * Allocate sufficient pages to preallocation for the requested number of
240 * notifications.
241 */
watch_queue_set_size(struct pipe_inode_info * pipe,unsigned int nr_notes)242 long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
243 {
244 struct watch_queue *wqueue = pipe->watch_queue;
245 struct page **pages;
246 unsigned long *bitmap;
247 unsigned long user_bufs;
248 unsigned int bmsize;
249 int ret, i, nr_pages;
250
251 if (!wqueue)
252 return -ENODEV;
253 if (wqueue->notes)
254 return -EBUSY;
255
256 if (nr_notes < 1 ||
257 nr_notes > 512) /* TODO: choose a better hard limit */
258 return -EINVAL;
259
260 nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1);
261 nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE;
262 user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages);
263
264 if (nr_pages > pipe->max_usage &&
265 (too_many_pipe_buffers_hard(user_bufs) ||
266 too_many_pipe_buffers_soft(user_bufs)) &&
267 pipe_is_unprivileged_user()) {
268 ret = -EPERM;
269 goto error;
270 }
271
272 nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE;
273 ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes));
274 if (ret < 0)
275 goto error;
276
277 ret = -ENOMEM;
278 pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL);
279 if (!pages)
280 goto error;
281
282 for (i = 0; i < nr_pages; i++) {
283 pages[i] = alloc_page(GFP_KERNEL);
284 if (!pages[i])
285 goto error_p;
286 pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE;
287 }
288
289 bmsize = (nr_notes + BITS_PER_LONG - 1) / BITS_PER_LONG;
290 bmsize *= sizeof(unsigned long);
291 bitmap = kmalloc(bmsize, GFP_KERNEL);
292 if (!bitmap)
293 goto error_p;
294
295 memset(bitmap, 0xff, bmsize);
296 wqueue->notes = pages;
297 wqueue->notes_bitmap = bitmap;
298 wqueue->nr_pages = nr_pages;
299 wqueue->nr_notes = nr_notes;
300 return 0;
301
302 error_p:
303 while (--i >= 0)
304 __free_page(pages[i]);
305 kfree(pages);
306 error:
307 (void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted);
308 return ret;
309 }
310
311 /*
312 * Set the filter on a watch queue.
313 */
watch_queue_set_filter(struct pipe_inode_info * pipe,struct watch_notification_filter __user * _filter)314 long watch_queue_set_filter(struct pipe_inode_info *pipe,
315 struct watch_notification_filter __user *_filter)
316 {
317 struct watch_notification_type_filter *tf;
318 struct watch_notification_filter filter;
319 struct watch_type_filter *q;
320 struct watch_filter *wfilter;
321 struct watch_queue *wqueue = pipe->watch_queue;
322 int ret, nr_filter = 0, i;
323
324 if (!wqueue)
325 return -ENODEV;
326
327 if (!_filter) {
328 /* Remove the old filter */
329 wfilter = NULL;
330 goto set;
331 }
332
333 /* Grab the user's filter specification */
334 if (copy_from_user(&filter, _filter, sizeof(filter)) != 0)
335 return -EFAULT;
336 if (filter.nr_filters == 0 ||
337 filter.nr_filters > 16 ||
338 filter.__reserved != 0)
339 return -EINVAL;
340
341 tf = memdup_array_user(_filter->filters, filter.nr_filters, sizeof(*tf));
342 if (IS_ERR(tf))
343 return PTR_ERR(tf);
344
345 ret = -EINVAL;
346 for (i = 0; i < filter.nr_filters; i++) {
347 if ((tf[i].info_filter & ~tf[i].info_mask) ||
348 tf[i].info_mask & WATCH_INFO_LENGTH)
349 goto err_filter;
350 /* Ignore any unknown types */
351 if (tf[i].type >= WATCH_TYPE__NR)
352 continue;
353 nr_filter++;
354 }
355
356 /* Now we need to build the internal filter from only the relevant
357 * user-specified filters.
358 */
359 ret = -ENOMEM;
360 wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL);
361 if (!wfilter)
362 goto err_filter;
363 wfilter->nr_filters = nr_filter;
364
365 q = wfilter->filters;
366 for (i = 0; i < filter.nr_filters; i++) {
367 if (tf[i].type >= WATCH_TYPE__NR)
368 continue;
369
370 q->type = tf[i].type;
371 q->info_filter = tf[i].info_filter;
372 q->info_mask = tf[i].info_mask;
373 q->subtype_filter[0] = tf[i].subtype_filter[0];
374 __set_bit(q->type, wfilter->type_filter);
375 q++;
376 }
377
378 kfree(tf);
379 set:
380 pipe_lock(pipe);
381 wfilter = rcu_replace_pointer(wqueue->filter, wfilter,
382 lockdep_is_held(&pipe->mutex));
383 pipe_unlock(pipe);
384 if (wfilter)
385 kfree_rcu(wfilter, rcu);
386 return 0;
387
388 err_filter:
389 kfree(tf);
390 return ret;
391 }
392
__put_watch_queue(struct kref * kref)393 static void __put_watch_queue(struct kref *kref)
394 {
395 struct watch_queue *wqueue =
396 container_of(kref, struct watch_queue, usage);
397 struct watch_filter *wfilter;
398 int i;
399
400 for (i = 0; i < wqueue->nr_pages; i++)
401 __free_page(wqueue->notes[i]);
402 kfree(wqueue->notes);
403 bitmap_free(wqueue->notes_bitmap);
404
405 wfilter = rcu_access_pointer(wqueue->filter);
406 if (wfilter)
407 kfree_rcu(wfilter, rcu);
408 kfree_rcu(wqueue, rcu);
409 }
410
411 /**
412 * put_watch_queue - Dispose of a ref on a watchqueue.
413 * @wqueue: The watch queue to unref.
414 */
put_watch_queue(struct watch_queue * wqueue)415 void put_watch_queue(struct watch_queue *wqueue)
416 {
417 kref_put(&wqueue->usage, __put_watch_queue);
418 }
419 EXPORT_SYMBOL(put_watch_queue);
420
free_watch(struct rcu_head * rcu)421 static void free_watch(struct rcu_head *rcu)
422 {
423 struct watch *watch = container_of(rcu, struct watch, rcu);
424
425 put_watch_queue(rcu_access_pointer(watch->queue));
426 atomic_dec(&watch->cred->user->nr_watches);
427 put_cred(watch->cred);
428 kfree(watch);
429 }
430
__put_watch(struct kref * kref)431 static void __put_watch(struct kref *kref)
432 {
433 struct watch *watch = container_of(kref, struct watch, usage);
434
435 call_rcu(&watch->rcu, free_watch);
436 }
437
438 /*
439 * Discard a watch.
440 */
put_watch(struct watch * watch)441 static void put_watch(struct watch *watch)
442 {
443 kref_put(&watch->usage, __put_watch);
444 }
445
446 /**
447 * init_watch - Initialise a watch
448 * @watch: The watch to initialise.
449 * @wqueue: The queue to assign.
450 *
451 * Initialise a watch and set the watch queue.
452 */
init_watch(struct watch * watch,struct watch_queue * wqueue)453 void init_watch(struct watch *watch, struct watch_queue *wqueue)
454 {
455 kref_init(&watch->usage);
456 INIT_HLIST_NODE(&watch->list_node);
457 INIT_HLIST_NODE(&watch->queue_node);
458 rcu_assign_pointer(watch->queue, wqueue);
459 }
460
add_one_watch(struct watch * watch,struct watch_list * wlist,struct watch_queue * wqueue)461 static int add_one_watch(struct watch *watch, struct watch_list *wlist, struct watch_queue *wqueue)
462 {
463 const struct cred *cred;
464 struct watch *w;
465
466 hlist_for_each_entry(w, &wlist->watchers, list_node) {
467 struct watch_queue *wq = rcu_access_pointer(w->queue);
468 if (wqueue == wq && watch->id == w->id)
469 return -EBUSY;
470 }
471
472 cred = current_cred();
473 if (atomic_inc_return(&cred->user->nr_watches) > task_rlimit(current, RLIMIT_NOFILE)) {
474 atomic_dec(&cred->user->nr_watches);
475 return -EAGAIN;
476 }
477
478 watch->cred = get_cred(cred);
479 rcu_assign_pointer(watch->watch_list, wlist);
480
481 kref_get(&wqueue->usage);
482 kref_get(&watch->usage);
483 hlist_add_head(&watch->queue_node, &wqueue->watches);
484 hlist_add_head_rcu(&watch->list_node, &wlist->watchers);
485 return 0;
486 }
487
488 /**
489 * add_watch_to_object - Add a watch on an object to a watch list
490 * @watch: The watch to add
491 * @wlist: The watch list to add to
492 *
493 * @watch->queue must have been set to point to the queue to post notifications
494 * to and the watch list of the object to be watched. @watch->cred must also
495 * have been set to the appropriate credentials and a ref taken on them.
496 *
497 * The caller must pin the queue and the list both and must hold the list
498 * locked against racing watch additions/removals.
499 */
add_watch_to_object(struct watch * watch,struct watch_list * wlist)500 int add_watch_to_object(struct watch *watch, struct watch_list *wlist)
501 {
502 struct watch_queue *wqueue;
503 int ret = -ENOENT;
504
505 rcu_read_lock();
506
507 wqueue = rcu_access_pointer(watch->queue);
508 if (lock_wqueue(wqueue)) {
509 spin_lock(&wlist->lock);
510 ret = add_one_watch(watch, wlist, wqueue);
511 spin_unlock(&wlist->lock);
512 unlock_wqueue(wqueue);
513 }
514
515 rcu_read_unlock();
516 return ret;
517 }
518 EXPORT_SYMBOL(add_watch_to_object);
519
520 /**
521 * remove_watch_from_object - Remove a watch or all watches from an object.
522 * @wlist: The watch list to remove from
523 * @wq: The watch queue of interest (ignored if @all is true)
524 * @id: The ID of the watch to remove (ignored if @all is true)
525 * @all: True to remove all objects
526 *
527 * Remove a specific watch or all watches from an object. A notification is
528 * sent to the watcher to tell them that this happened.
529 */
remove_watch_from_object(struct watch_list * wlist,struct watch_queue * wq,u64 id,bool all)530 int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq,
531 u64 id, bool all)
532 {
533 struct watch_notification_removal n;
534 struct watch_queue *wqueue;
535 struct watch *watch;
536 int ret = -EBADSLT;
537
538 rcu_read_lock();
539
540 again:
541 spin_lock(&wlist->lock);
542 hlist_for_each_entry(watch, &wlist->watchers, list_node) {
543 if (all ||
544 (watch->id == id && rcu_access_pointer(watch->queue) == wq))
545 goto found;
546 }
547 spin_unlock(&wlist->lock);
548 goto out;
549
550 found:
551 ret = 0;
552 hlist_del_init_rcu(&watch->list_node);
553 rcu_assign_pointer(watch->watch_list, NULL);
554 spin_unlock(&wlist->lock);
555
556 /* We now own the reference on watch that used to belong to wlist. */
557
558 n.watch.type = WATCH_TYPE_META;
559 n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION;
560 n.watch.info = watch->info_id | watch_sizeof(n.watch);
561 n.id = id;
562 if (id != 0)
563 n.watch.info = watch->info_id | watch_sizeof(n);
564
565 wqueue = rcu_dereference(watch->queue);
566
567 if (lock_wqueue(wqueue)) {
568 post_one_notification(wqueue, &n.watch);
569
570 if (!hlist_unhashed(&watch->queue_node)) {
571 hlist_del_init_rcu(&watch->queue_node);
572 put_watch(watch);
573 }
574
575 unlock_wqueue(wqueue);
576 }
577
578 if (wlist->release_watch) {
579 void (*release_watch)(struct watch *);
580
581 release_watch = wlist->release_watch;
582 rcu_read_unlock();
583 (*release_watch)(watch);
584 rcu_read_lock();
585 }
586 put_watch(watch);
587
588 if (all && !hlist_empty(&wlist->watchers))
589 goto again;
590 out:
591 rcu_read_unlock();
592 return ret;
593 }
594 EXPORT_SYMBOL(remove_watch_from_object);
595
596 /*
597 * Remove all the watches that are contributory to a queue. This has the
598 * potential to race with removal of the watches by the destruction of the
599 * objects being watched or with the distribution of notifications.
600 */
watch_queue_clear(struct watch_queue * wqueue)601 void watch_queue_clear(struct watch_queue *wqueue)
602 {
603 struct watch_list *wlist;
604 struct watch *watch;
605 bool release;
606
607 rcu_read_lock();
608 spin_lock_bh(&wqueue->lock);
609
610 /* Prevent new notifications from being stored. */
611 wqueue->defunct = true;
612
613 while (!hlist_empty(&wqueue->watches)) {
614 watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);
615 hlist_del_init_rcu(&watch->queue_node);
616 /* We now own a ref on the watch. */
617 spin_unlock_bh(&wqueue->lock);
618
619 /* We can't do the next bit under the queue lock as we need to
620 * get the list lock - which would cause a deadlock if someone
621 * was removing from the opposite direction at the same time or
622 * posting a notification.
623 */
624 wlist = rcu_dereference(watch->watch_list);
625 if (wlist) {
626 void (*release_watch)(struct watch *);
627
628 spin_lock(&wlist->lock);
629
630 release = !hlist_unhashed(&watch->list_node);
631 if (release) {
632 hlist_del_init_rcu(&watch->list_node);
633 rcu_assign_pointer(watch->watch_list, NULL);
634
635 /* We now own a second ref on the watch. */
636 }
637
638 release_watch = wlist->release_watch;
639 spin_unlock(&wlist->lock);
640
641 if (release) {
642 if (release_watch) {
643 rcu_read_unlock();
644 /* This might need to call dput(), so
645 * we have to drop all the locks.
646 */
647 (*release_watch)(watch);
648 rcu_read_lock();
649 }
650 put_watch(watch);
651 }
652 }
653
654 put_watch(watch);
655 spin_lock_bh(&wqueue->lock);
656 }
657
658 spin_unlock_bh(&wqueue->lock);
659 rcu_read_unlock();
660 }
661
662 /**
663 * get_watch_queue - Get a watch queue from its file descriptor.
664 * @fd: The fd to query.
665 */
get_watch_queue(int fd)666 struct watch_queue *get_watch_queue(int fd)
667 {
668 struct pipe_inode_info *pipe;
669 struct watch_queue *wqueue = ERR_PTR(-EINVAL);
670 struct fd f;
671
672 f = fdget(fd);
673 if (f.file) {
674 pipe = get_pipe_info(f.file, false);
675 if (pipe && pipe->watch_queue) {
676 wqueue = pipe->watch_queue;
677 kref_get(&wqueue->usage);
678 }
679 fdput(f);
680 }
681
682 return wqueue;
683 }
684 EXPORT_SYMBOL(get_watch_queue);
685
686 /*
687 * Initialise a watch queue
688 */
watch_queue_init(struct pipe_inode_info * pipe)689 int watch_queue_init(struct pipe_inode_info *pipe)
690 {
691 struct watch_queue *wqueue;
692
693 wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL);
694 if (!wqueue)
695 return -ENOMEM;
696
697 wqueue->pipe = pipe;
698 kref_init(&wqueue->usage);
699 spin_lock_init(&wqueue->lock);
700 INIT_HLIST_HEAD(&wqueue->watches);
701
702 pipe->watch_queue = wqueue;
703 return 0;
704 }
705