// 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_recalc_mask(struct fsnotify_mark_connector *conn)

  {
  	u32 new_mask = 0;
  	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;

  	hlist_for_each_entry(mark, &conn->list, obj_list) {
  		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
  			new_mask |= mark->mask;
  	}

  	*fsnotify_conn_mask_p(conn) = new_mask;

  }
  
  /*
   * 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_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;

  		atomic_long_inc(&inode->i_sb->s_fsnotify_inode_refs);

  	} 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;

  	}

  	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)
  {
  	struct inode *inode;
  	struct super_block *sb;
  
  	if (!objp)
  		return;
  	/* Currently only inode references are passed to be dropped */
  	if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
  		return;
  	inode = objp;
  	sb = inode->i_sb;
  	iput(inode);
  	if (atomic_long_dec_and_test(&sb->s_fsnotify_inode_refs))
  		wake_up_var(&sb->s_fsnotify_inode_refs);
  }

  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 {
  		__fsnotify_recalc_mask(conn);

  	}

  	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_obj_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_obj_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)

  {

  	struct fsnotify_group *group = mark->group;

  	WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
  	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);

  	atomic_dec(&group->num_marks);

  
  	/* 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)
  {

  	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);

  	fsnotify_detach_mark(mark);

  	mutex_unlock(&group->mark_mutex);

  	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 type,
  					       __kernel_fsid_t *fsid)

  {

  	struct inode *inode = NULL;

  	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->type = 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;
  	}

  	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)

  		inode = igrab(fsnotify_conn_inode(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 */

  		if (inode)
  			iput(inode);

  		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 type,

  				  int allow_dups, __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(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, 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
  ", __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) &&
  		    !allow_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 type,

  			     int allow_dups, __kernel_fsid_t *fsid)

  {

  	struct fsnotify_group *group = mark->group;

  	int ret = 0;

  	BUG_ON(!mutex_is_locked(&group->mark_mutex));

  
  	/*

  	 * 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);
  	atomic_inc(&group->num_marks);

  	fsnotify_get_mark(mark); /* for g_list */

  	spin_unlock(&mark->lock);

  	ret = fsnotify_add_mark_list(mark, connp, type, allow_dups, fsid);

  	if (ret)
  		goto err;

  	if (mark->mask)
  		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);

  	atomic_dec(&group->num_marks);

  	fsnotify_put_mark(mark);

  	return ret;
  }

  int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,

  		      unsigned int type, int allow_dups, __kernel_fsid_t *fsid)

  {
  	int ret;

  	struct fsnotify_group *group = mark->group;

  	mutex_lock(&group->mark_mutex);

  	ret = fsnotify_add_mark_locked(mark, connp, type, allow_dups, fsid);

  	mutex_unlock(&group->mark_mutex);
  	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 type_mask)

  {
  	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 (type_mask == FSNOTIFY_OBJ_ALL_TYPES_MASK) {

  		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.
  	 */

  	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);

  	list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {

  		if ((1U << mark->connector->type) & type_mask)

  			list_move(&mark->g_list, &to_free);

  	}

  	mutex_unlock(&group->mark_mutex);

  clear:

  	while (1) {
  		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);

  		if (list_empty(head)) {

  			mutex_unlock(&group->mark_mutex);
  			break;
  		}

  		mark = list_first_entry(head, struct fsnotify_mark, g_list);

  		fsnotify_get_mark(mark);

  		fsnotify_detach_mark(mark);

  		mutex_unlock(&group->mark_mutex);

  		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);