root/fs/notify/mark.c

DEFINITIONS

1. fsnotify_get_mark
2. fsnotify_conn_mask_p
3. fsnotify_conn_mask
4. __fsnotify_recalc_mask
5. fsnotify_recalc_mask
6. fsnotify_connector_destroy_workfn
7. fsnotify_detach_connector_from_object
8. fsnotify_final_mark_destroy
9. fsnotify_drop_object
10. fsnotify_put_mark
11. fsnotify_get_mark_safe
12. fsnotify_put_mark_wake
13. fsnotify_prepare_user_wait
14. fsnotify_finish_user_wait
15. fsnotify_detach_mark
16. fsnotify_free_mark
17. fsnotify_destroy_mark
18. fsnotify_compare_groups
19. fsnotify_attach_connector_to_object
20. fsnotify_grab_connector
21. fsnotify_add_mark_list
22. fsnotify_add_mark_locked
23. fsnotify_add_mark
24. fsnotify_find_mark
25. fsnotify_clear_marks_by_group
26. fsnotify_destroy_marks
27. fsnotify_init_mark
28. fsnotify_mark_destroy_workfn
29. fsnotify_wait_marks_destroyed

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
   4  */
   5 
   6 /*
   7  * fsnotify inode mark locking/lifetime/and refcnting
   8  *
   9  * REFCNT:
  10  * The group->recnt and mark->refcnt tell how many "things" in the kernel
  11  * currently are referencing the objects. Both kind of objects typically will
  12  * live inside the kernel with a refcnt of 2, one for its creation and one for
  13  * the reference a group and a mark hold to each other.
  14  * If you are holding the appropriate locks, you can take a reference and the
  15  * object itself is guaranteed to survive until the reference is dropped.
  16  *
  17  * LOCKING:
  18  * There are 3 locks involved with fsnotify inode marks and they MUST be taken
  19  * in order as follows:
  20  *
  21  * group->mark_mutex
  22  * mark->lock
  23  * mark->connector->lock
  24  *
  25  * group->mark_mutex protects the marks_list anchored inside a given group and
  26  * each mark is hooked via the g_list.  It also protects the groups private
  27  * data (i.e group limits).
  28 
  29  * mark->lock protects the marks attributes like its masks and flags.
  30  * Furthermore it protects the access to a reference of the group that the mark
  31  * is assigned to as well as the access to a reference of the inode/vfsmount
  32  * that is being watched by the mark.
  33  *
  34  * mark->connector->lock protects the list of marks anchored inside an
  35  * inode / vfsmount and each mark is hooked via the i_list.
  36  *
  37  * A list of notification marks relating to inode / mnt is contained in
  38  * fsnotify_mark_connector. That structure is alive as long as there are any
  39  * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
  40  * detached from fsnotify_mark_connector when last reference to the mark is
  41  * dropped.  Thus having mark reference is enough to protect mark->connector
  42  * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
  43  * because we remove mark from g_list before dropping mark reference associated
  44  * with that, any mark found through g_list is guaranteed to have
  45  * mark->connector set until we drop group->mark_mutex.
  46  *
  47  * LIFETIME:
  48  * Inode marks survive between when they are added to an inode and when their
  49  * refcnt==0. Marks are also protected by fsnotify_mark_srcu.
  50  *
  51  * The inode mark can be cleared for a number of different reasons including:
  52  * - The inode is unlinked for the last time.  (fsnotify_inode_remove)
  53  * - The inode is being evicted from cache. (fsnotify_inode_delete)
  54  * - The fs the inode is on is unmounted.  (fsnotify_inode_delete/fsnotify_unmount_inodes)
  55  * - Something explicitly requests that it be removed.  (fsnotify_destroy_mark)
  56  * - The fsnotify_group associated with the mark is going away and all such marks
  57  *   need to be cleaned up. (fsnotify_clear_marks_by_group)
  58  *
  59  * This has the very interesting property of being able to run concurrently with
  60  * any (or all) other directions.
  61  */
  62 
  63 #include <linux/fs.h>
  64 #include <linux/init.h>
  65 #include <linux/kernel.h>
  66 #include <linux/kthread.h>
  67 #include <linux/module.h>
  68 #include <linux/mutex.h>
  69 #include <linux/slab.h>
  70 #include <linux/spinlock.h>
  71 #include <linux/srcu.h>
  72 #include <linux/ratelimit.h>
  73 
  74 #include <linux/atomic.h>
  75 
  76 #include <linux/fsnotify_backend.h>
  77 #include "fsnotify.h"
  78 
  79 #define FSNOTIFY_REAPER_DELAY   (1)     /* 1 jiffy */
  80 
  81 struct srcu_struct fsnotify_mark_srcu;
  82 struct kmem_cache *fsnotify_mark_connector_cachep;
  83 
  84 static DEFINE_SPINLOCK(destroy_lock);
  85 static LIST_HEAD(destroy_list);
  86 static struct fsnotify_mark_connector *connector_destroy_list;
  87 
  88 static void fsnotify_mark_destroy_workfn(struct work_struct *work);
  89 static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn);
  90 
  91 static void fsnotify_connector_destroy_workfn(struct work_struct *work);
  92 static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
  93 
  94 void fsnotify_get_mark(struct fsnotify_mark *mark)
  95 {
  96         WARN_ON_ONCE(!refcount_read(&mark->refcnt));
  97         refcount_inc(&mark->refcnt);
  98 }
  99 
 100 static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn)
 101 {
 102         if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
 103                 return &fsnotify_conn_inode(conn)->i_fsnotify_mask;
 104         else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
 105                 return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask;
 106         else if (conn->type == FSNOTIFY_OBJ_TYPE_SB)
 107                 return &fsnotify_conn_sb(conn)->s_fsnotify_mask;
 108         return NULL;
 109 }
 110 
 111 __u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn)
 112 {
 113         if (WARN_ON(!fsnotify_valid_obj_type(conn->type)))
 114                 return 0;
 115 
 116         return *fsnotify_conn_mask_p(conn);
 117 }
 118 
 119 static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 120 {
 121         u32 new_mask = 0;
 122         struct fsnotify_mark *mark;
 123 
 124         assert_spin_locked(&conn->lock);
 125         /* We can get detached connector here when inode is getting unlinked. */
 126         if (!fsnotify_valid_obj_type(conn->type))
 127                 return;
 128         hlist_for_each_entry(mark, &conn->list, obj_list) {
 129                 if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
 130                         new_mask |= mark->mask;
 131         }
 132         *fsnotify_conn_mask_p(conn) = new_mask;
 133 }
 134 
 135 /*
 136  * Calculate mask of events for a list of marks. The caller must make sure
 137  * connector and connector->obj cannot disappear under us.  Callers achieve
 138  * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
 139  * list.
 140  */
 141 void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 142 {
 143         if (!conn)
 144                 return;
 145 
 146         spin_lock(&conn->lock);
 147         __fsnotify_recalc_mask(conn);
 148         spin_unlock(&conn->lock);
 149         if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
 150                 __fsnotify_update_child_dentry_flags(
 151                                         fsnotify_conn_inode(conn));
 152 }
 153 
 154 /* Free all connectors queued for freeing once SRCU period ends */
 155 static void fsnotify_connector_destroy_workfn(struct work_struct *work)
 156 {
 157         struct fsnotify_mark_connector *conn, *free;
 158 
 159         spin_lock(&destroy_lock);
 160         conn = connector_destroy_list;
 161         connector_destroy_list = NULL;
 162         spin_unlock(&destroy_lock);
 163 
 164         synchronize_srcu(&fsnotify_mark_srcu);
 165         while (conn) {
 166                 free = conn;
 167                 conn = conn->destroy_next;
 168                 kmem_cache_free(fsnotify_mark_connector_cachep, free);
 169         }
 170 }
 171 
 172 static void *fsnotify_detach_connector_from_object(
 173                                         struct fsnotify_mark_connector *conn,
 174                                         unsigned int *type)
 175 {
 176         struct inode *inode = NULL;
 177 
 178         *type = conn->type;
 179         if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED)
 180                 return NULL;
 181 
 182         if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
 183                 inode = fsnotify_conn_inode(conn);
 184                 inode->i_fsnotify_mask = 0;
 185                 atomic_long_inc(&inode->i_sb->s_fsnotify_inode_refs);
 186         } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
 187                 fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0;
 188         } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) {
 189                 fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
 190         }
 191 
 192         rcu_assign_pointer(*(conn->obj), NULL);
 193         conn->obj = NULL;
 194         conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
 195 
 196         return inode;
 197 }
 198 
 199 static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
 200 {
 201         struct fsnotify_group *group = mark->group;
 202 
 203         if (WARN_ON_ONCE(!group))
 204                 return;
 205         group->ops->free_mark(mark);
 206         fsnotify_put_group(group);
 207 }
 208 
 209 /* Drop object reference originally held by a connector */
 210 static void fsnotify_drop_object(unsigned int type, void *objp)
 211 {
 212         struct inode *inode;
 213         struct super_block *sb;
 214 
 215         if (!objp)
 216                 return;
 217         /* Currently only inode references are passed to be dropped */
 218         if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
 219                 return;
 220         inode = objp;
 221         sb = inode->i_sb;
 222         iput(inode);
 223         if (atomic_long_dec_and_test(&sb->s_fsnotify_inode_refs))
 224                 wake_up_var(&sb->s_fsnotify_inode_refs);
 225 }
 226 
 227 void fsnotify_put_mark(struct fsnotify_mark *mark)
 228 {
 229         struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
 230         void *objp = NULL;
 231         unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
 232         bool free_conn = false;
 233 
 234         /* Catch marks that were actually never attached to object */
 235         if (!conn) {
 236                 if (refcount_dec_and_test(&mark->refcnt))
 237                         fsnotify_final_mark_destroy(mark);
 238                 return;
 239         }
 240 
 241         /*
 242          * We have to be careful so that traversals of obj_list under lock can
 243          * safely grab mark reference.
 244          */
 245         if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
 246                 return;
 247 
 248         hlist_del_init_rcu(&mark->obj_list);
 249         if (hlist_empty(&conn->list)) {
 250                 objp = fsnotify_detach_connector_from_object(conn, &type);
 251                 free_conn = true;
 252         } else {
 253                 __fsnotify_recalc_mask(conn);
 254         }
 255         WRITE_ONCE(mark->connector, NULL);
 256         spin_unlock(&conn->lock);
 257 
 258         fsnotify_drop_object(type, objp);
 259 
 260         if (free_conn) {
 261                 spin_lock(&destroy_lock);
 262                 conn->destroy_next = connector_destroy_list;
 263                 connector_destroy_list = conn;
 264                 spin_unlock(&destroy_lock);
 265                 queue_work(system_unbound_wq, &connector_reaper_work);
 266         }
 267         /*
 268          * Note that we didn't update flags telling whether inode cares about
 269          * what's happening with children. We update these flags from
 270          * __fsnotify_parent() lazily when next event happens on one of our
 271          * children.
 272          */
 273         spin_lock(&destroy_lock);
 274         list_add(&mark->g_list, &destroy_list);
 275         spin_unlock(&destroy_lock);
 276         queue_delayed_work(system_unbound_wq, &reaper_work,
 277                            FSNOTIFY_REAPER_DELAY);
 278 }
 279 EXPORT_SYMBOL_GPL(fsnotify_put_mark);
 280 
 281 /*
 282  * Get mark reference when we found the mark via lockless traversal of object
 283  * list. Mark can be already removed from the list by now and on its way to be
 284  * destroyed once SRCU period ends.
 285  *
 286  * Also pin the group so it doesn't disappear under us.
 287  */
 288 static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
 289 {
 290         if (!mark)
 291                 return true;
 292 
 293         if (refcount_inc_not_zero(&mark->refcnt)) {
 294                 spin_lock(&mark->lock);
 295                 if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
 296                         /* mark is attached, group is still alive then */
 297                         atomic_inc(&mark->group->user_waits);
 298                         spin_unlock(&mark->lock);
 299                         return true;
 300                 }
 301                 spin_unlock(&mark->lock);
 302                 fsnotify_put_mark(mark);
 303         }
 304         return false;
 305 }
 306 
 307 /*
 308  * Puts marks and wakes up group destruction if necessary.
 309  *
 310  * Pairs with fsnotify_get_mark_safe()
 311  */
 312 static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
 313 {
 314         if (mark) {
 315                 struct fsnotify_group *group = mark->group;
 316 
 317                 fsnotify_put_mark(mark);
 318                 /*
 319                  * We abuse notification_waitq on group shutdown for waiting for
 320                  * all marks pinned when waiting for userspace.
 321                  */
 322                 if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
 323                         wake_up(&group->notification_waitq);
 324         }
 325 }
 326 
 327 bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
 328 {
 329         int type;
 330 
 331         fsnotify_foreach_obj_type(type) {
 332                 /* This can fail if mark is being removed */
 333                 if (!fsnotify_get_mark_safe(iter_info->marks[type]))
 334                         goto fail;
 335         }
 336 
 337         /*
 338          * Now that both marks are pinned by refcount in the inode / vfsmount
 339          * lists, we can drop SRCU lock, and safely resume the list iteration
 340          * once userspace returns.
 341          */
 342         srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
 343 
 344         return true;
 345 
 346 fail:
 347         for (type--; type >= 0; type--)
 348                 fsnotify_put_mark_wake(iter_info->marks[type]);
 349         return false;
 350 }
 351 
 352 void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
 353 {
 354         int type;
 355 
 356         iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
 357         fsnotify_foreach_obj_type(type)
 358                 fsnotify_put_mark_wake(iter_info->marks[type]);
 359 }
 360 
 361 /*
 362  * Mark mark as detached, remove it from group list. Mark still stays in object
 363  * list until its last reference is dropped. Note that we rely on mark being
 364  * removed from group list before corresponding reference to it is dropped. In
 365  * particular we rely on mark->connector being valid while we hold
 366  * group->mark_mutex if we found the mark through g_list.
 367  *
 368  * Must be called with group->mark_mutex held. The caller must either hold
 369  * reference to the mark or be protected by fsnotify_mark_srcu.
 370  */
 371 void fsnotify_detach_mark(struct fsnotify_mark *mark)
 372 {
 373         struct fsnotify_group *group = mark->group;
 374 
 375         WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
 376         WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
 377                      refcount_read(&mark->refcnt) < 1 +
 378                         !!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
 379 
 380         spin_lock(&mark->lock);
 381         /* something else already called this function on this mark */
 382         if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
 383                 spin_unlock(&mark->lock);
 384                 return;
 385         }
 386         mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
 387         list_del_init(&mark->g_list);
 388         spin_unlock(&mark->lock);
 389 
 390         atomic_dec(&group->num_marks);
 391 
 392         /* Drop mark reference acquired in fsnotify_add_mark_locked() */
 393         fsnotify_put_mark(mark);
 394 }
 395 
 396 /*
 397  * Free fsnotify mark. The mark is actually only marked as being freed.  The
 398  * freeing is actually happening only once last reference to the mark is
 399  * dropped from a workqueue which first waits for srcu period end.
 400  *
 401  * Caller must have a reference to the mark or be protected by
 402  * fsnotify_mark_srcu.
 403  */
 404 void fsnotify_free_mark(struct fsnotify_mark *mark)
 405 {
 406         struct fsnotify_group *group = mark->group;
 407 
 408         spin_lock(&mark->lock);
 409         /* something else already called this function on this mark */
 410         if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
 411                 spin_unlock(&mark->lock);
 412                 return;
 413         }
 414         mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
 415         spin_unlock(&mark->lock);
 416 
 417         /*
 418          * Some groups like to know that marks are being freed.  This is a
 419          * callback to the group function to let it know that this mark
 420          * is being freed.
 421          */
 422         if (group->ops->freeing_mark)
 423                 group->ops->freeing_mark(mark, group);
 424 }
 425 
 426 void fsnotify_destroy_mark(struct fsnotify_mark *mark,
 427                            struct fsnotify_group *group)
 428 {
 429         mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
 430         fsnotify_detach_mark(mark);
 431         mutex_unlock(&group->mark_mutex);
 432         fsnotify_free_mark(mark);
 433 }
 434 EXPORT_SYMBOL_GPL(fsnotify_destroy_mark);
 435 
 436 /*
 437  * Sorting function for lists of fsnotify marks.
 438  *
 439  * Fanotify supports different notification classes (reflected as priority of
 440  * notification group). Events shall be passed to notification groups in
 441  * decreasing priority order. To achieve this marks in notification lists for
 442  * inodes and vfsmounts are sorted so that priorities of corresponding groups
 443  * are descending.
 444  *
 445  * Furthermore correct handling of the ignore mask requires processing inode
 446  * and vfsmount marks of each group together. Using the group address as
 447  * further sort criterion provides a unique sorting order and thus we can
 448  * merge inode and vfsmount lists of marks in linear time and find groups
 449  * present in both lists.
 450  *
 451  * A return value of 1 signifies that b has priority over a.
 452  * A return value of 0 signifies that the two marks have to be handled together.
 453  * A return value of -1 signifies that a has priority over b.
 454  */
 455 int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
 456 {
 457         if (a == b)
 458                 return 0;
 459         if (!a)
 460                 return 1;
 461         if (!b)
 462                 return -1;
 463         if (a->priority < b->priority)
 464                 return 1;
 465         if (a->priority > b->priority)
 466                 return -1;
 467         if (a < b)
 468                 return 1;
 469         return -1;
 470 }
 471 
 472 static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
 473                                                unsigned int type,
 474                                                __kernel_fsid_t *fsid)
 475 {
 476         struct inode *inode = NULL;
 477         struct fsnotify_mark_connector *conn;
 478 
 479         conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
 480         if (!conn)
 481                 return -ENOMEM;
 482         spin_lock_init(&conn->lock);
 483         INIT_HLIST_HEAD(&conn->list);
 484         conn->type = type;
 485         conn->obj = connp;
 486         /* Cache fsid of filesystem containing the object */
 487         if (fsid) {
 488                 conn->fsid = *fsid;
 489                 conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID;
 490         } else {
 491                 conn->fsid.val[0] = conn->fsid.val[1] = 0;
 492                 conn->flags = 0;
 493         }
 494         if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
 495                 inode = igrab(fsnotify_conn_inode(conn));
 496         /*
 497          * cmpxchg() provides the barrier so that readers of *connp can see
 498          * only initialized structure
 499          */
 500         if (cmpxchg(connp, NULL, conn)) {
 501                 /* Someone else created list structure for us */
 502                 if (inode)
 503                         iput(inode);
 504                 kmem_cache_free(fsnotify_mark_connector_cachep, conn);
 505         }
 506 
 507         return 0;
 508 }
 509 
 510 /*
 511  * Get mark connector, make sure it is alive and return with its lock held.
 512  * This is for users that get connector pointer from inode or mount. Users that
 513  * hold reference to a mark on the list may directly lock connector->lock as
 514  * they are sure list cannot go away under them.
 515  */
 516 static struct fsnotify_mark_connector *fsnotify_grab_connector(
 517                                                 fsnotify_connp_t *connp)
 518 {
 519         struct fsnotify_mark_connector *conn;
 520         int idx;
 521 
 522         idx = srcu_read_lock(&fsnotify_mark_srcu);
 523         conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
 524         if (!conn)
 525                 goto out;
 526         spin_lock(&conn->lock);
 527         if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
 528                 spin_unlock(&conn->lock);
 529                 srcu_read_unlock(&fsnotify_mark_srcu, idx);
 530                 return NULL;
 531         }
 532 out:
 533         srcu_read_unlock(&fsnotify_mark_srcu, idx);
 534         return conn;
 535 }
 536 
 537 /*
 538  * Add mark into proper place in given list of marks. These marks may be used
 539  * for the fsnotify backend to determine which event types should be delivered
 540  * to which group and for which inodes. These marks are ordered according to
 541  * priority, highest number first, and then by the group's location in memory.
 542  */
 543 static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
 544                                   fsnotify_connp_t *connp, unsigned int type,
 545                                   int allow_dups, __kernel_fsid_t *fsid)
 546 {
 547         struct fsnotify_mark *lmark, *last = NULL;
 548         struct fsnotify_mark_connector *conn;
 549         int cmp;
 550         int err = 0;
 551 
 552         if (WARN_ON(!fsnotify_valid_obj_type(type)))
 553                 return -EINVAL;
 554 
 555         /* Backend is expected to check for zero fsid (e.g. tmpfs) */
 556         if (fsid && WARN_ON_ONCE(!fsid->val[0] && !fsid->val[1]))
 557                 return -ENODEV;
 558 
 559 restart:
 560         spin_lock(&mark->lock);
 561         conn = fsnotify_grab_connector(connp);
 562         if (!conn) {
 563                 spin_unlock(&mark->lock);
 564                 err = fsnotify_attach_connector_to_object(connp, type, fsid);
 565                 if (err)
 566                         return err;
 567                 goto restart;
 568         } else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) {
 569                 conn->fsid = *fsid;
 570                 /* Pairs with smp_rmb() in fanotify_get_fsid() */
 571                 smp_wmb();
 572                 conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID;
 573         } else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) &&
 574                    (fsid->val[0] != conn->fsid.val[0] ||
 575                     fsid->val[1] != conn->fsid.val[1])) {
 576                 /*
 577                  * Backend is expected to check for non uniform fsid
 578                  * (e.g. btrfs), but maybe we missed something?
 579                  * Only allow setting conn->fsid once to non zero fsid.
 580                  * inotify and non-fid fanotify groups do not set nor test
 581                  * conn->fsid.
 582                  */
 583                 pr_warn_ratelimited("%s: fsid mismatch on object of type %u: "
 584                                     "%x.%x != %x.%x\n", __func__, conn->type,
 585                                     fsid->val[0], fsid->val[1],
 586                                     conn->fsid.val[0], conn->fsid.val[1]);
 587                 err = -EXDEV;
 588                 goto out_err;
 589         }
 590 
 591         /* is mark the first mark? */
 592         if (hlist_empty(&conn->list)) {
 593                 hlist_add_head_rcu(&mark->obj_list, &conn->list);
 594                 goto added;
 595         }
 596 
 597         /* should mark be in the middle of the current list? */
 598         hlist_for_each_entry(lmark, &conn->list, obj_list) {
 599                 last = lmark;
 600 
 601                 if ((lmark->group == mark->group) &&
 602                     (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
 603                     !allow_dups) {
 604                         err = -EEXIST;
 605                         goto out_err;
 606                 }
 607 
 608                 cmp = fsnotify_compare_groups(lmark->group, mark->group);
 609                 if (cmp >= 0) {
 610                         hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
 611                         goto added;
 612                 }
 613         }
 614 
 615         BUG_ON(last == NULL);
 616         /* mark should be the last entry.  last is the current last entry */
 617         hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
 618 added:
 619         /*
 620          * Since connector is attached to object using cmpxchg() we are
 621          * guaranteed that connector initialization is fully visible by anyone
 622          * seeing mark->connector set.
 623          */
 624         WRITE_ONCE(mark->connector, conn);
 625 out_err:
 626         spin_unlock(&conn->lock);
 627         spin_unlock(&mark->lock);
 628         return err;
 629 }
 630 
 631 /*
 632  * Attach an initialized mark to a given group and fs object.
 633  * These marks may be used for the fsnotify backend to determine which
 634  * event types should be delivered to which group.
 635  */
 636 int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
 637                              fsnotify_connp_t *connp, unsigned int type,
 638                              int allow_dups, __kernel_fsid_t *fsid)
 639 {
 640         struct fsnotify_group *group = mark->group;
 641         int ret = 0;
 642 
 643         BUG_ON(!mutex_is_locked(&group->mark_mutex));
 644 
 645         /*
 646          * LOCKING ORDER!!!!
 647          * group->mark_mutex
 648          * mark->lock
 649          * mark->connector->lock
 650          */
 651         spin_lock(&mark->lock);
 652         mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
 653 
 654         list_add(&mark->g_list, &group->marks_list);
 655         atomic_inc(&group->num_marks);
 656         fsnotify_get_mark(mark); /* for g_list */
 657         spin_unlock(&mark->lock);
 658 
 659         ret = fsnotify_add_mark_list(mark, connp, type, allow_dups, fsid);
 660         if (ret)
 661                 goto err;
 662 
 663         if (mark->mask)
 664                 fsnotify_recalc_mask(mark->connector);
 665 
 666         return ret;
 667 err:
 668         spin_lock(&mark->lock);
 669         mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
 670                          FSNOTIFY_MARK_FLAG_ATTACHED);
 671         list_del_init(&mark->g_list);
 672         spin_unlock(&mark->lock);
 673         atomic_dec(&group->num_marks);
 674 
 675         fsnotify_put_mark(mark);
 676         return ret;
 677 }
 678 
 679 int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,
 680                       unsigned int type, int allow_dups, __kernel_fsid_t *fsid)
 681 {
 682         int ret;
 683         struct fsnotify_group *group = mark->group;
 684 
 685         mutex_lock(&group->mark_mutex);
 686         ret = fsnotify_add_mark_locked(mark, connp, type, allow_dups, fsid);
 687         mutex_unlock(&group->mark_mutex);
 688         return ret;
 689 }
 690 EXPORT_SYMBOL_GPL(fsnotify_add_mark);
 691 
 692 /*
 693  * Given a list of marks, find the mark associated with given group. If found
 694  * take a reference to that mark and return it, else return NULL.
 695  */
 696 struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp,
 697                                          struct fsnotify_group *group)
 698 {
 699         struct fsnotify_mark_connector *conn;
 700         struct fsnotify_mark *mark;
 701 
 702         conn = fsnotify_grab_connector(connp);
 703         if (!conn)
 704                 return NULL;
 705 
 706         hlist_for_each_entry(mark, &conn->list, obj_list) {
 707                 if (mark->group == group &&
 708                     (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
 709                         fsnotify_get_mark(mark);
 710                         spin_unlock(&conn->lock);
 711                         return mark;
 712                 }
 713         }
 714         spin_unlock(&conn->lock);
 715         return NULL;
 716 }
 717 EXPORT_SYMBOL_GPL(fsnotify_find_mark);
 718 
 719 /* Clear any marks in a group with given type mask */
 720 void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
 721                                    unsigned int type_mask)
 722 {
 723         struct fsnotify_mark *lmark, *mark;
 724         LIST_HEAD(to_free);
 725         struct list_head *head = &to_free;
 726 
 727         /* Skip selection step if we want to clear all marks. */
 728         if (type_mask == FSNOTIFY_OBJ_ALL_TYPES_MASK) {
 729                 head = &group->marks_list;
 730                 goto clear;
 731         }
 732         /*
 733          * We have to be really careful here. Anytime we drop mark_mutex, e.g.
 734          * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
 735          * to_free list so we have to use mark_mutex even when accessing that
 736          * list. And freeing mark requires us to drop mark_mutex. So we can
 737          * reliably free only the first mark in the list. That's why we first
 738          * move marks to free to to_free list in one go and then free marks in
 739          * to_free list one by one.
 740          */
 741         mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
 742         list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
 743                 if ((1U << mark->connector->type) & type_mask)
 744                         list_move(&mark->g_list, &to_free);
 745         }
 746         mutex_unlock(&group->mark_mutex);
 747 
 748 clear:
 749         while (1) {
 750                 mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
 751                 if (list_empty(head)) {
 752                         mutex_unlock(&group->mark_mutex);
 753                         break;
 754                 }
 755                 mark = list_first_entry(head, struct fsnotify_mark, g_list);
 756                 fsnotify_get_mark(mark);
 757                 fsnotify_detach_mark(mark);
 758                 mutex_unlock(&group->mark_mutex);
 759                 fsnotify_free_mark(mark);
 760                 fsnotify_put_mark(mark);
 761         }
 762 }
 763 
 764 /* Destroy all marks attached to an object via connector */
 765 void fsnotify_destroy_marks(fsnotify_connp_t *connp)
 766 {
 767         struct fsnotify_mark_connector *conn;
 768         struct fsnotify_mark *mark, *old_mark = NULL;
 769         void *objp;
 770         unsigned int type;
 771 
 772         conn = fsnotify_grab_connector(connp);
 773         if (!conn)
 774                 return;
 775         /*
 776          * We have to be careful since we can race with e.g.
 777          * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
 778          * list can get modified. However we are holding mark reference and
 779          * thus our mark cannot be removed from obj_list so we can continue
 780          * iteration after regaining conn->lock.
 781          */
 782         hlist_for_each_entry(mark, &conn->list, obj_list) {
 783                 fsnotify_get_mark(mark);
 784                 spin_unlock(&conn->lock);
 785                 if (old_mark)
 786                         fsnotify_put_mark(old_mark);
 787                 old_mark = mark;
 788                 fsnotify_destroy_mark(mark, mark->group);
 789                 spin_lock(&conn->lock);
 790         }
 791         /*
 792          * Detach list from object now so that we don't pin inode until all
 793          * mark references get dropped. It would lead to strange results such
 794          * as delaying inode deletion or blocking unmount.
 795          */
 796         objp = fsnotify_detach_connector_from_object(conn, &type);
 797         spin_unlock(&conn->lock);
 798         if (old_mark)
 799                 fsnotify_put_mark(old_mark);
 800         fsnotify_drop_object(type, objp);
 801 }
 802 
 803 /*
 804  * Nothing fancy, just initialize lists and locks and counters.
 805  */
 806 void fsnotify_init_mark(struct fsnotify_mark *mark,
 807                         struct fsnotify_group *group)
 808 {
 809         memset(mark, 0, sizeof(*mark));
 810         spin_lock_init(&mark->lock);
 811         refcount_set(&mark->refcnt, 1);
 812         fsnotify_get_group(group);
 813         mark->group = group;
 814         WRITE_ONCE(mark->connector, NULL);
 815 }
 816 EXPORT_SYMBOL_GPL(fsnotify_init_mark);
 817 
 818 /*
 819  * Destroy all marks in destroy_list, waits for SRCU period to finish before
 820  * actually freeing marks.
 821  */
 822 static void fsnotify_mark_destroy_workfn(struct work_struct *work)
 823 {
 824         struct fsnotify_mark *mark, *next;
 825         struct list_head private_destroy_list;
 826 
 827         spin_lock(&destroy_lock);
 828         /* exchange the list head */
 829         list_replace_init(&destroy_list, &private_destroy_list);
 830         spin_unlock(&destroy_lock);
 831 
 832         synchronize_srcu(&fsnotify_mark_srcu);
 833 
 834         list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
 835                 list_del_init(&mark->g_list);
 836                 fsnotify_final_mark_destroy(mark);
 837         }
 838 }
 839 
 840 /* Wait for all marks queued for destruction to be actually destroyed */
 841 void fsnotify_wait_marks_destroyed(void)
 842 {
 843         flush_delayed_work(&reaper_work);
 844 }
 845 EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed);