kernel/watch_queue.c

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