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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
  */
 
 /*
  * fsnotify inode mark locking/lifetime/and refcnting
  *
  * REFCNT:
  * The group->recnt and mark->refcnt tell how many "things" in the kernel
  * currently are referencing the objects. Both kind of objects typically will
  * live inside the kernel with a refcnt of 2, one for its creation and one for
  * the reference a group and a mark hold to each other.
  * If you are holding the appropriate locks, you can take a reference and the
  * object itself is guaranteed to survive until the reference is dropped.
  *
  * LOCKING:
  * There are 3 locks involved with fsnotify inode marks and they MUST be taken
  * in order as follows:
  *
  * group->mark_mutex
  * mark->lock
  * mark->connector->lock
  *
  * group->mark_mutex protects the marks_list anchored inside a given group and
  * each mark is hooked via the g_list.  It also protects the groups private
  * data (i.e group limits).
 
  * mark->lock protects the marks attributes like its masks and flags.
  * Furthermore it protects the access to a reference of the group that the mark
  * is assigned to as well as the access to a reference of the inode/vfsmount
  * that is being watched by the mark.
  *
  * mark->connector->lock protects the list of marks anchored inside an
  * inode / vfsmount and each mark is hooked via the i_list.
  *
  * A list of notification marks relating to inode / mnt is contained in
  * fsnotify_mark_connector. That structure is alive as long as there are any
  * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
  * detached from fsnotify_mark_connector when last reference to the mark is
  * dropped.  Thus having mark reference is enough to protect mark->connector
  * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
  * because we remove mark from g_list before dropping mark reference associated
  * with that, any mark found through g_list is guaranteed to have
  * mark->connector set until we drop group->mark_mutex.
  *
  * LIFETIME:
  * Inode marks survive between when they are added to an inode and when their
  * refcnt==0. Marks are also protected by fsnotify_mark_srcu.
  *
  * The inode mark can be cleared for a number of different reasons including:
  * - The inode is unlinked for the last time.  (fsnotify_inode_remove)
  * - The inode is being evicted from cache. (fsnotify_inode_delete)
  * - The fs the inode is on is unmounted.  (fsnotify_inode_delete/fsnotify_unmount_inodes)
  * - Something explicitly requests that it be removed.  (fsnotify_destroy_mark)
  * - The fsnotify_group associated with the mark is going away and all such marks
  *   need to be cleaned up. (fsnotify_clear_marks_by_group)
  *
  * This has the very interesting property of being able to run concurrently with
  * any (or all) other directions.
  */
 
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/kthread.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/srcu.h>
 #include <linux/ratelimit.h>
 
 #include <linux/atomic.h>
 
 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"
 
 #define FSNOTIFY_REAPER_DELAY   (1) /* 1 jiffy */
 
 struct srcu_struct fsnotify_mark_srcu;
 struct kmem_cache *fsnotify_mark_connector_cachep;
 
 static DEFINE_SPINLOCK(destroy_lock);
 static LIST_HEAD(destroy_list);
 static struct fsnotify_mark_connector *connector_destroy_list;
 
 static void fsnotify_mark_destroy_workfn(struct work_struct *work);
 static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn);
 
 static void fsnotify_connector_destroy_workfn(struct work_struct *work);
 static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
 
 void fsnotify_get_mark(struct fsnotify_mark *mark)
 {
     WARN_ON_ONCE(!refcount_read(&mark->refcnt));
     refcount_inc(&mark->refcnt);
 }
 
 static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn)
 {
     if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
         return &fsnotify_conn_inode(conn)->i_fsnotify_mask;
     else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
         return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask;
     else if (conn->type == FSNOTIFY_OBJ_TYPE_SB)
         return &fsnotify_conn_sb(conn)->s_fsnotify_mask;
     return NULL;
 }
 
 __u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn)
 {
     if (WARN_ON(!fsnotify_valid_obj_type(conn->type)))
         return 0;
 
     return *fsnotify_conn_mask_p(conn);
 }
 
 static void fsnotify_get_inode_ref(struct inode *inode)
 {
     ihold(inode);
     atomic_long_inc(&inode->i_sb->s_fsnotify_connectors);
 }
 
 /*
  * Grab or drop inode reference for the connector if needed.
  *
  * When it's time to drop the reference, we only clear the HAS_IREF flag and
  * return the inode object. fsnotify_drop_object() will be resonsible for doing
  * iput() outside of spinlocks. This happens when last mark that wanted iref is
  * detached.
  */
 static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn,
                       bool want_iref)
 {
     bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF;
     struct inode *inode = NULL;
 
     if (conn->type != FSNOTIFY_OBJ_TYPE_INODE ||
         want_iref == has_iref)
         return NULL;
 
     if (want_iref) {
         /* Pin inode if any mark wants inode refcount held */
         fsnotify_get_inode_ref(fsnotify_conn_inode(conn));
         conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF;
     } else {
         /* Unpin inode after detach of last mark that wanted iref */
         inode = fsnotify_conn_inode(conn);
         conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF;
     }
 
     return inode;
 }
 
 static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 {
     u32 new_mask = 0;
     bool want_iref = false;
     struct fsnotify_mark *mark;
 
     assert_spin_locked(&conn->lock);
     /* We can get detached connector here when inode is getting unlinked. */
     if (!fsnotify_valid_obj_type(conn->type))
         return NULL;
     hlist_for_each_entry(mark, &conn->list, obj_list) {
         if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
             continue;
         new_mask |= fsnotify_calc_mask(mark);
         if (conn->type == FSNOTIFY_OBJ_TYPE_INODE &&
             !(mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF))
             want_iref = true;
     }
     *fsnotify_conn_mask_p(conn) = new_mask;
 
     return fsnotify_update_iref(conn, want_iref);
 }
 
 /*
  * Calculate mask of events for a list of marks. The caller must make sure
  * connector and connector->obj cannot disappear under us.  Callers achieve
  * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
  * list.
  */
 void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 {
     if (!conn)
         return;
 
     spin_lock(&conn->lock);
     __fsnotify_recalc_mask(conn);
     spin_unlock(&conn->lock);
     if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
         __fsnotify_update_child_dentry_flags(
                     fsnotify_conn_inode(conn));
 }
 
 /* Free all connectors queued for freeing once SRCU period ends */
 static void fsnotify_connector_destroy_workfn(struct work_struct *work)
 {
     struct fsnotify_mark_connector *conn, *free;
 
     spin_lock(&destroy_lock);
     conn = connector_destroy_list;
     connector_destroy_list = NULL;
     spin_unlock(&destroy_lock);
 
     synchronize_srcu(&fsnotify_mark_srcu);
     while (conn) {
         free = conn;
         conn = conn->destroy_next;
         kmem_cache_free(fsnotify_mark_connector_cachep, free);
     }
 }
 
 static void fsnotify_put_inode_ref(struct inode *inode)
 {
     struct super_block *sb = inode->i_sb;
 
     iput(inode);
     if (atomic_long_dec_and_test(&sb->s_fsnotify_connectors))
         wake_up_var(&sb->s_fsnotify_connectors);
 }
 
 static void fsnotify_get_sb_connectors(struct fsnotify_mark_connector *conn)
 {
     struct super_block *sb = fsnotify_connector_sb(conn);
 
     if (sb)
         atomic_long_inc(&sb->s_fsnotify_connectors);
 }
 
 static void fsnotify_put_sb_connectors(struct fsnotify_mark_connector *conn)
 {
     struct super_block *sb = fsnotify_connector_sb(conn);
 
     if (sb && atomic_long_dec_and_test(&sb->s_fsnotify_connectors))
         wake_up_var(&sb->s_fsnotify_connectors);
 }
 
 static void *fsnotify_detach_connector_from_object(
                     struct fsnotify_mark_connector *conn,
                     unsigned int *type)
 {
     struct inode *inode = NULL;
 
     *type = conn->type;
     if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED)
         return NULL;
 
     if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
         inode = fsnotify_conn_inode(conn);
         inode->i_fsnotify_mask = 0;
 
         /* Unpin inode when detaching from connector */
         if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF))
             inode = NULL;
     } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
         fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0;
     } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) {
         fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
     }
 
     fsnotify_put_sb_connectors(conn);
     rcu_assign_pointer(*(conn->obj), NULL);
     conn->obj = NULL;
     conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
 
     return inode;
 }
 
 static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
 {
     struct fsnotify_group *group = mark->group;
 
     if (WARN_ON_ONCE(!group))
         return;
     group->ops->free_mark(mark);
     fsnotify_put_group(group);
 }
 
 /* Drop object reference originally held by a connector */
 static void fsnotify_drop_object(unsigned int type, void *objp)
 {
     if (!objp)
         return;
     /* Currently only inode references are passed to be dropped */
     if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
         return;
     fsnotify_put_inode_ref(objp);
 }
 
 void fsnotify_put_mark(struct fsnotify_mark *mark)
 {
     struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
     void *objp = NULL;
     unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
     bool free_conn = false;
 
     /* Catch marks that were actually never attached to object */
     if (!conn) {
         if (refcount_dec_and_test(&mark->refcnt))
             fsnotify_final_mark_destroy(mark);
         return;
     }
 
     /*
      * We have to be careful so that traversals of obj_list under lock can
      * safely grab mark reference.
      */
     if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
         return;
 
     hlist_del_init_rcu(&mark->obj_list);
     if (hlist_empty(&conn->list)) {
         objp = fsnotify_detach_connector_from_object(conn, &type);
         free_conn = true;
     } else {
         objp = __fsnotify_recalc_mask(conn);
         type = conn->type;
     }
     WRITE_ONCE(mark->connector, NULL);
     spin_unlock(&conn->lock);
 
     fsnotify_drop_object(type, objp);
 
     if (free_conn) {
         spin_lock(&destroy_lock);
         conn->destroy_next = connector_destroy_list;
         connector_destroy_list = conn;
         spin_unlock(&destroy_lock);
         queue_work(system_unbound_wq, &connector_reaper_work);
     }
     /*
      * Note that we didn't update flags telling whether inode cares about
      * what's happening with children. We update these flags from
      * __fsnotify_parent() lazily when next event happens on one of our
      * children.
      */
     spin_lock(&destroy_lock);
     list_add(&mark->g_list, &destroy_list);
     spin_unlock(&destroy_lock);
     queue_delayed_work(system_unbound_wq, &reaper_work,
                FSNOTIFY_REAPER_DELAY);
 }
 EXPORT_SYMBOL_GPL(fsnotify_put_mark);
 
 /*
  * Get mark reference when we found the mark via lockless traversal of object
  * list. Mark can be already removed from the list by now and on its way to be
  * destroyed once SRCU period ends.
  *
  * Also pin the group so it doesn't disappear under us.
  */
 static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
 {
     if (!mark)
         return true;
 
     if (refcount_inc_not_zero(&mark->refcnt)) {
         spin_lock(&mark->lock);
         if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
             /* mark is attached, group is still alive then */
             atomic_inc(&mark->group->user_waits);
             spin_unlock(&mark->lock);
             return true;
         }
         spin_unlock(&mark->lock);
         fsnotify_put_mark(mark);
     }
     return false;
 }
 
 /*
  * Puts marks and wakes up group destruction if necessary.
  *
  * Pairs with fsnotify_get_mark_safe()
  */
 static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
 {
     if (mark) {
         struct fsnotify_group *group = mark->group;
 
         fsnotify_put_mark(mark);
         /*
          * We abuse notification_waitq on group shutdown for waiting for
          * all marks pinned when waiting for userspace.
          */
         if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
             wake_up(&group->notification_waitq);
     }
 }
 
 bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
     __releases(&fsnotify_mark_srcu)
 {
     int type;
 
     fsnotify_foreach_iter_type(type) {
         /* This can fail if mark is being removed */
         if (!fsnotify_get_mark_safe(iter_info->marks[type])) {
             __release(&fsnotify_mark_srcu);
             goto fail;
         }
     }
 
     /*
      * Now that both marks are pinned by refcount in the inode / vfsmount
      * lists, we can drop SRCU lock, and safely resume the list iteration
      * once userspace returns.
      */
     srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
 
     return true;
 
 fail:
     for (type--; type >= 0; type--)
         fsnotify_put_mark_wake(iter_info->marks[type]);
     return false;
 }
 
 void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
     __acquires(&fsnotify_mark_srcu)
 {
     int type;
 
     iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
     fsnotify_foreach_iter_type(type)
         fsnotify_put_mark_wake(iter_info->marks[type]);
 }
 
 /*
  * Mark mark as detached, remove it from group list. Mark still stays in object
  * list until its last reference is dropped. Note that we rely on mark being
  * removed from group list before corresponding reference to it is dropped. In
  * particular we rely on mark->connector being valid while we hold
  * group->mark_mutex if we found the mark through g_list.
  *
  * Must be called with group->mark_mutex held. The caller must either hold
  * reference to the mark or be protected by fsnotify_mark_srcu.
  */
 void fsnotify_detach_mark(struct fsnotify_mark *mark)
 {
     fsnotify_group_assert_locked(mark->group);
     WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
              refcount_read(&mark->refcnt) < 1 +
             !!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
 
     spin_lock(&mark->lock);
     /* something else already called this function on this mark */
     if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
         spin_unlock(&mark->lock);
         return;
     }
     mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
     list_del_init(&mark->g_list);
     spin_unlock(&mark->lock);
 
     /* Drop mark reference acquired in fsnotify_add_mark_locked() */
     fsnotify_put_mark(mark);
 }
 
 /*
  * Free fsnotify mark. The mark is actually only marked as being freed.  The
  * freeing is actually happening only once last reference to the mark is
  * dropped from a workqueue which first waits for srcu period end.
  *
  * Caller must have a reference to the mark or be protected by
  * fsnotify_mark_srcu.
  */
 void fsnotify_free_mark(struct fsnotify_mark *mark)
 {
     struct fsnotify_group *group = mark->group;
 
     spin_lock(&mark->lock);
     /* something else already called this function on this mark */
     if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
         spin_unlock(&mark->lock);
         return;
     }
     mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
     spin_unlock(&mark->lock);
 
     /*
      * Some groups like to know that marks are being freed.  This is a
      * callback to the group function to let it know that this mark
      * is being freed.
      */
     if (group->ops->freeing_mark)
         group->ops->freeing_mark(mark, group);
 }
 
 void fsnotify_destroy_mark(struct fsnotify_mark *mark,
                struct fsnotify_group *group)
 {
     fsnotify_group_lock(group);
     fsnotify_detach_mark(mark);
     fsnotify_group_unlock(group);
     fsnotify_free_mark(mark);
 }
 EXPORT_SYMBOL_GPL(fsnotify_destroy_mark);
 
 /*
  * Sorting function for lists of fsnotify marks.
  *
  * Fanotify supports different notification classes (reflected as priority of
  * notification group). Events shall be passed to notification groups in
  * decreasing priority order. To achieve this marks in notification lists for
  * inodes and vfsmounts are sorted so that priorities of corresponding groups
  * are descending.
  *
  * Furthermore correct handling of the ignore mask requires processing inode
  * and vfsmount marks of each group together. Using the group address as
  * further sort criterion provides a unique sorting order and thus we can
  * merge inode and vfsmount lists of marks in linear time and find groups
  * present in both lists.
  *
  * A return value of 1 signifies that b has priority over a.
  * A return value of 0 signifies that the two marks have to be handled together.
  * A return value of -1 signifies that a has priority over b.
  */
 int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
 {
     if (a == b)
         return 0;
     if (!a)
         return 1;
     if (!b)
         return -1;
     if (a->priority < b->priority)
         return 1;
     if (a->priority > b->priority)
         return -1;
     if (a < b)
         return 1;
     return -1;
 }
 
 static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
                            unsigned int obj_type,
                            __kernel_fsid_t *fsid)
 {
     struct fsnotify_mark_connector *conn;
 
     conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
     if (!conn)
         return -ENOMEM;
     spin_lock_init(&conn->lock);
     INIT_HLIST_HEAD(&conn->list);
     conn->flags = 0;
     conn->type = obj_type;
     conn->obj = connp;
     /* Cache fsid of filesystem containing the object */
     if (fsid) {
         conn->fsid = *fsid;
         conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID;
     } else {
         conn->fsid.val[0] = conn->fsid.val[1] = 0;
         conn->flags = 0;
     }
     fsnotify_get_sb_connectors(conn);
 
     /*
      * cmpxchg() provides the barrier so that readers of *connp can see
      * only initialized structure
      */
     if (cmpxchg(connp, NULL, conn)) {
         /* Someone else created list structure for us */
         fsnotify_put_sb_connectors(conn);
         kmem_cache_free(fsnotify_mark_connector_cachep, conn);
     }
 
     return 0;
 }
 
 /*
  * Get mark connector, make sure it is alive and return with its lock held.
  * This is for users that get connector pointer from inode or mount. Users that
  * hold reference to a mark on the list may directly lock connector->lock as
  * they are sure list cannot go away under them.
  */
 static struct fsnotify_mark_connector *fsnotify_grab_connector(
                         fsnotify_connp_t *connp)
 {
     struct fsnotify_mark_connector *conn;
     int idx;
 
     idx = srcu_read_lock(&fsnotify_mark_srcu);
     conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
     if (!conn)
         goto out;
     spin_lock(&conn->lock);
     if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
         spin_unlock(&conn->lock);
         srcu_read_unlock(&fsnotify_mark_srcu, idx);
         return NULL;
     }
 out:
     srcu_read_unlock(&fsnotify_mark_srcu, idx);
     return conn;
 }
 
 /*
  * Add mark into proper place in given list of marks. These marks may be used
  * for the fsnotify backend to determine which event types should be delivered
  * to which group and for which inodes. These marks are ordered according to
  * priority, highest number first, and then by the group's location in memory.
  */
 static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
                   fsnotify_connp_t *connp,
                   unsigned int obj_type,
                   int add_flags, __kernel_fsid_t *fsid)
 {
     struct fsnotify_mark *lmark, *last = NULL;
     struct fsnotify_mark_connector *conn;
     int cmp;
     int err = 0;
 
     if (WARN_ON(!fsnotify_valid_obj_type(obj_type)))
         return -EINVAL;
 
     /* Backend is expected to check for zero fsid (e.g. tmpfs) */
     if (fsid && WARN_ON_ONCE(!fsid->val[0] && !fsid->val[1]))
         return -ENODEV;
 
 restart:
     spin_lock(&mark->lock);
     conn = fsnotify_grab_connector(connp);
     if (!conn) {
         spin_unlock(&mark->lock);
         err = fsnotify_attach_connector_to_object(connp, obj_type,
                               fsid);
         if (err)
             return err;
         goto restart;
     } else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) {
         conn->fsid = *fsid;
         /* Pairs with smp_rmb() in fanotify_get_fsid() */
         smp_wmb();
         conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID;
     } else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) &&
            (fsid->val[0] != conn->fsid.val[0] ||
             fsid->val[1] != conn->fsid.val[1])) {
         /*
          * Backend is expected to check for non uniform fsid
          * (e.g. btrfs), but maybe we missed something?
          * Only allow setting conn->fsid once to non zero fsid.
          * inotify and non-fid fanotify groups do not set nor test
          * conn->fsid.
          */
         pr_warn_ratelimited("%s: fsid mismatch on object of type %u: "
                     "%x.%x != %x.%x\n", __func__, conn->type,
                     fsid->val[0], fsid->val[1],
                     conn->fsid.val[0], conn->fsid.val[1]);
         err = -EXDEV;
         goto out_err;
     }
 
     /* is mark the first mark? */
     if (hlist_empty(&conn->list)) {
         hlist_add_head_rcu(&mark->obj_list, &conn->list);
         goto added;
     }
 
     /* should mark be in the middle of the current list? */
     hlist_for_each_entry(lmark, &conn->list, obj_list) {
         last = lmark;
 
         if ((lmark->group == mark->group) &&
             (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
             !(mark->group->flags & FSNOTIFY_GROUP_DUPS)) {
             err = -EEXIST;
             goto out_err;
         }
 
         cmp = fsnotify_compare_groups(lmark->group, mark->group);
         if (cmp >= 0) {
             hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
             goto added;
         }
     }
 
     BUG_ON(last == NULL);
     /* mark should be the last entry.  last is the current last entry */
     hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
 added:
     /*
      * Since connector is attached to object using cmpxchg() we are
      * guaranteed that connector initialization is fully visible by anyone
      * seeing mark->connector set.
      */
     WRITE_ONCE(mark->connector, conn);
 out_err:
     spin_unlock(&conn->lock);
     spin_unlock(&mark->lock);
     return err;
 }
 
 /*
  * Attach an initialized mark to a given group and fs object.
  * These marks may be used for the fsnotify backend to determine which
  * event types should be delivered to which group.
  */
 int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
                  fsnotify_connp_t *connp, unsigned int obj_type,
                  int add_flags, __kernel_fsid_t *fsid)
 {
     struct fsnotify_group *group = mark->group;
     int ret = 0;
 
     fsnotify_group_assert_locked(group);
 
     /*
      * LOCKING ORDER!!!!
      * group->mark_mutex
      * mark->lock
      * mark->connector->lock
      */
     spin_lock(&mark->lock);
     mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
 
     list_add(&mark->g_list, &group->marks_list);
     fsnotify_get_mark(mark); /* for g_list */
     spin_unlock(&mark->lock);
 
     ret = fsnotify_add_mark_list(mark, connp, obj_type, add_flags, fsid);
     if (ret)
         goto err;
 
     fsnotify_recalc_mask(mark->connector);
 
     return ret;
 err:
     spin_lock(&mark->lock);
     mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
              FSNOTIFY_MARK_FLAG_ATTACHED);
     list_del_init(&mark->g_list);
     spin_unlock(&mark->lock);
 
     fsnotify_put_mark(mark);
     return ret;
 }
 
 int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,
               unsigned int obj_type, int add_flags,
               __kernel_fsid_t *fsid)
 {
     int ret;
     struct fsnotify_group *group = mark->group;
 
     fsnotify_group_lock(group);
     ret = fsnotify_add_mark_locked(mark, connp, obj_type, add_flags, fsid);
     fsnotify_group_unlock(group);
     return ret;
 }
 EXPORT_SYMBOL_GPL(fsnotify_add_mark);
 
 /*
  * Given a list of marks, find the mark associated with given group. If found
  * take a reference to that mark and return it, else return NULL.
  */
 struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp,
                      struct fsnotify_group *group)
 {
     struct fsnotify_mark_connector *conn;
     struct fsnotify_mark *mark;
 
     conn = fsnotify_grab_connector(connp);
     if (!conn)
         return NULL;
 
     hlist_for_each_entry(mark, &conn->list, obj_list) {
         if (mark->group == group &&
             (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
             fsnotify_get_mark(mark);
             spin_unlock(&conn->lock);
             return mark;
         }
     }
     spin_unlock(&conn->lock);
     return NULL;
 }
 EXPORT_SYMBOL_GPL(fsnotify_find_mark);
 
 /* Clear any marks in a group with given type mask */
 void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
                    unsigned int obj_type)
 {
     struct fsnotify_mark *lmark, *mark;
     LIST_HEAD(to_free);
     struct list_head *head = &to_free;
 
     /* Skip selection step if we want to clear all marks. */
     if (obj_type == FSNOTIFY_OBJ_TYPE_ANY) {
         head = &group->marks_list;
         goto clear;
     }
     /*
      * We have to be really careful here. Anytime we drop mark_mutex, e.g.
      * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
      * to_free list so we have to use mark_mutex even when accessing that
      * list. And freeing mark requires us to drop mark_mutex. So we can
      * reliably free only the first mark in the list. That's why we first
      * move marks to free to to_free list in one go and then free marks in
      * to_free list one by one.
      */
     fsnotify_group_lock(group);
     list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
         if (mark->connector->type == obj_type)
             list_move(&mark->g_list, &to_free);
     }
     fsnotify_group_unlock(group);
 
 clear:
     while (1) {
         fsnotify_group_lock(group);
         if (list_empty(head)) {
             fsnotify_group_unlock(group);
             break;
         }
         mark = list_first_entry(head, struct fsnotify_mark, g_list);
         fsnotify_get_mark(mark);
         fsnotify_detach_mark(mark);
         fsnotify_group_unlock(group);
         fsnotify_free_mark(mark);
         fsnotify_put_mark(mark);
     }
 }
 
 /* Destroy all marks attached to an object via connector */
 void fsnotify_destroy_marks(fsnotify_connp_t *connp)
 {
     struct fsnotify_mark_connector *conn;
     struct fsnotify_mark *mark, *old_mark = NULL;
     void *objp;
     unsigned int type;
 
     conn = fsnotify_grab_connector(connp);
     if (!conn)
         return;
     /*
      * We have to be careful since we can race with e.g.
      * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
      * list can get modified. However we are holding mark reference and
      * thus our mark cannot be removed from obj_list so we can continue
      * iteration after regaining conn->lock.
      */
     hlist_for_each_entry(mark, &conn->list, obj_list) {
         fsnotify_get_mark(mark);
         spin_unlock(&conn->lock);
         if (old_mark)
             fsnotify_put_mark(old_mark);
         old_mark = mark;
         fsnotify_destroy_mark(mark, mark->group);
         spin_lock(&conn->lock);
     }
     /*
      * Detach list from object now so that we don't pin inode until all
      * mark references get dropped. It would lead to strange results such
      * as delaying inode deletion or blocking unmount.
      */
     objp = fsnotify_detach_connector_from_object(conn, &type);
     spin_unlock(&conn->lock);
     if (old_mark)
         fsnotify_put_mark(old_mark);
     fsnotify_drop_object(type, objp);
 }
 
 /*
  * Nothing fancy, just initialize lists and locks and counters.
  */
 void fsnotify_init_mark(struct fsnotify_mark *mark,
             struct fsnotify_group *group)
 {
     memset(mark, 0, sizeof(*mark));
     spin_lock_init(&mark->lock);
     refcount_set(&mark->refcnt, 1);
     fsnotify_get_group(group);
     mark->group = group;
     WRITE_ONCE(mark->connector, NULL);
 }
 EXPORT_SYMBOL_GPL(fsnotify_init_mark);
 
 /*
  * Destroy all marks in destroy_list, waits for SRCU period to finish before
  * actually freeing marks.
  */
 static void fsnotify_mark_destroy_workfn(struct work_struct *work)
 {
     struct fsnotify_mark *mark, *next;
     struct list_head private_destroy_list;
 
     spin_lock(&destroy_lock);
     /* exchange the list head */
     list_replace_init(&destroy_list, &private_destroy_list);
     spin_unlock(&destroy_lock);
 
     synchronize_srcu(&fsnotify_mark_srcu);
 
     list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
         list_del_init(&mark->g_list);
         fsnotify_final_mark_destroy(mark);
     }
 }
 
 /* Wait for all marks queued for destruction to be actually destroyed */
 void fsnotify_wait_marks_destroyed(void)
 {
     flush_delayed_work(&reaper_work);
 }
 EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed);

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