fs/notify/mark.c - kernel/msm-4.9 - Gitiles

 /*
  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2, or (at your option)
  *  any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; see the file COPYING.  If not, write to
  *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  */

 /*
  * 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
  * inode->i_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.
  *
  * inode->i_lock protects the i_fsnotify_marks list anchored inside a
  * given inode and each mark is hooked via the i_list. (and sorta the
  * free_i_list)
  *
  *
  * LIFETIME:
  * Inode marks survive between when they are added to an inode and when their
  * refcnt==0.
  *
  * 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)
  *
  * Worst case we are given an inode and need to clean up all the marks on that
  * inode.  We take i_lock and walk the i_fsnotify_marks safely.  For each
  * mark on the list we take a reference (so the mark can't disappear under us).
  * We remove that mark form the inode's list of marks and we add this mark to a
  * private list anchored on the stack using i_free_list; we walk i_free_list
  * and before we destroy the mark we make sure that we dont race with a
  * concurrent destroy_group by getting a ref to the marks group and taking the
  * groups mutex.

  * Very similarly for freeing by group, except we use free_g_list.
  *
  * 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/atomic.h>

 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"

 struct srcu_struct fsnotify_mark_srcu;
 static DEFINE_SPINLOCK(destroy_lock);
 static LIST_HEAD(destroy_list);
 static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);

 void fsnotify_get_mark(struct fsnotify_mark *mark)
 {
 	atomic_inc(&mark->refcnt);
 }

 void fsnotify_put_mark(struct fsnotify_mark *mark)
 {
 	if (atomic_dec_and_test(&mark->refcnt)) {
 		if (mark->group)
 			fsnotify_put_group(mark->group);
 		mark->free_mark(mark);
 	}
 }

 /* Calculate mask of events for a list of marks */
 u32 fsnotify_recalc_mask(struct hlist_head *head)
 {
 	u32 new_mask = 0;
 	struct fsnotify_mark *mark;

 	hlist_for_each_entry(mark, head, obj_list)
 		new_mask |= mark->mask;
 	return new_mask;
 }

 /*
  * Any time a mark is getting freed we end up here.
  * The caller had better be holding a reference to this mark so we don't actually
  * do the final put under the mark->lock
  */
 void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
 				  struct fsnotify_group *group)
 {
 	struct inode *inode = NULL;

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

 	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;

 	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
 		inode = mark->inode;
 		fsnotify_destroy_inode_mark(mark);
 	} else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
 		fsnotify_destroy_vfsmount_mark(mark);
 	else
 		BUG();

 	list_del_init(&mark->g_list);

 	spin_unlock(&mark->lock);

 	if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
 		iput(inode);
 	/* release lock temporarily */
 	mutex_unlock(&group->mark_mutex);

 	spin_lock(&destroy_lock);
 	list_add(&mark->g_list, &destroy_list);
 	spin_unlock(&destroy_lock);
 	wake_up(&destroy_waitq);
 	/*
 	 * We don't necessarily have a ref on mark from caller so the above destroy
 	 * may have actually freed it, unless this group provides a 'freeing_mark'
 	 * function which must be holding a reference.
 	 */

 	/*
 	 * 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);

 	/*
 	 * __fsnotify_update_child_dentry_flags(inode);
 	 *
 	 * I really want to call that, but we can't, we have no idea if the inode
 	 * still exists the second we drop the mark->lock.
 	 *
 	 * The next time an event arrive to this inode from one of it's children
 	 * __fsnotify_parent will see that the inode doesn't care about it's
 	 * children and will update all of these flags then.  So really this
 	 * is just a lazy update (and could be a perf win...)
 	 */

 	atomic_dec(&group->num_marks);

 	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
 }

 void fsnotify_destroy_mark(struct fsnotify_mark *mark,
 			   struct fsnotify_group *group)
 {
 	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
 	fsnotify_destroy_mark_locked(mark, group);
 	mutex_unlock(&group->mark_mutex);
 }

 /*
  * Destroy all marks in the given list. The marks must be already detached from
  * the original inode / vfsmount.
  */
 void fsnotify_destroy_marks(struct list_head *to_free)
 {
 	struct fsnotify_mark *mark, *lmark;
 	struct fsnotify_group *group;

 	list_for_each_entry_safe(mark, lmark, to_free, free_list) {
 		spin_lock(&mark->lock);
 		fsnotify_get_group(mark->group);
 		group = mark->group;
 		spin_unlock(&mark->lock);

 		fsnotify_destroy_mark(mark, group);
 		fsnotify_put_mark(mark);
 		fsnotify_put_group(group);
 	}
 }

 void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
 {
 	assert_spin_locked(&mark->lock);

 	mark->mask = mask;

 	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
 		fsnotify_set_inode_mark_mask_locked(mark, mask);
 }

 void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
 {
 	assert_spin_locked(&mark->lock);

 	mark->ignored_mask = mask;
 }

 /*
  * 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;
 }

 /* Add mark into proper place in given list of marks */
 int fsnotify_add_mark_list(struct hlist_head *head, struct fsnotify_mark *mark,
 			   int allow_dups)
 {
 	struct fsnotify_mark *lmark, *last = NULL;
 	int cmp;

 	/* is mark the first mark? */
 	if (hlist_empty(head)) {
 		hlist_add_head_rcu(&mark->obj_list, head);
 		return 0;
 	}

 	/* should mark be in the middle of the current list? */
 	hlist_for_each_entry(lmark, head, obj_list) {
 		last = lmark;

 		if ((lmark->group == mark->group) && !allow_dups)
 			return -EEXIST;

 		cmp = fsnotify_compare_groups(lmark->group, mark->group);
 		if (cmp >= 0) {
 			hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
 			return 0;
 		}
 	}

 	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);
 	return 0;
 }

 /*
  * 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,
 			     struct fsnotify_group *group, struct inode *inode,
 			     struct vfsmount *mnt, int allow_dups)
 {
 	int ret = 0;

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

 	/*
 	 * LOCKING ORDER!!!!
 	 * group->mark_mutex
 	 * mark->lock
 	 * inode->i_lock
 	 */
 	spin_lock(&mark->lock);
 	mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;

 	fsnotify_get_group(group);
 	mark->group = group;
 	list_add(&mark->g_list, &group->marks_list);
 	atomic_inc(&group->num_marks);
 	fsnotify_get_mark(mark); /* for i_list and g_list */

 	if (inode) {
 		ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
 		if (ret)
 			goto err;
 	} else if (mnt) {
 		ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
 		if (ret)
 			goto err;
 	} else {
 		BUG();
 	}

 	/* this will pin the object if appropriate */
 	fsnotify_set_mark_mask_locked(mark, mark->mask);
 	spin_unlock(&mark->lock);

 	if (inode)
 		__fsnotify_update_child_dentry_flags(inode);

 	return ret;
 err:
 	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
 	list_del_init(&mark->g_list);
 	fsnotify_put_group(group);
 	mark->group = NULL;
 	atomic_dec(&group->num_marks);

 	spin_unlock(&mark->lock);

 	spin_lock(&destroy_lock);
 	list_add(&mark->g_list, &destroy_list);
 	spin_unlock(&destroy_lock);
 	wake_up(&destroy_waitq);

 	return ret;
 }

 int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
 		      struct inode *inode, struct vfsmount *mnt, int allow_dups)
 {
 	int ret;
 	mutex_lock(&group->mark_mutex);
 	ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
 	mutex_unlock(&group->mark_mutex);
 	return ret;
 }

 /*
  * 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(struct hlist_head *head,
 					 struct fsnotify_group *group)
 {
 	struct fsnotify_mark *mark;

 	hlist_for_each_entry(mark, head, obj_list) {
 		if (mark->group == group) {
 			fsnotify_get_mark(mark);
 			return mark;
 		}
 	}
 	return NULL;
 }

 /*
  * clear any marks in a group in which mark->flags & flags is true
  */
 void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
 					 unsigned int flags)
 {
 	struct fsnotify_mark *lmark, *mark;
 	LIST_HEAD(to_free);

 	/*
 	 * 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 (mark->flags & flags)
 			list_move(&mark->g_list, &to_free);
 	}
 	mutex_unlock(&group->mark_mutex);

 	while (1) {
 		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
 		if (list_empty(&to_free)) {
 			mutex_unlock(&group->mark_mutex);
 			break;
 		}
 		mark = list_first_entry(&to_free, struct fsnotify_mark, g_list);
 		fsnotify_get_mark(mark);
 		fsnotify_destroy_mark_locked(mark, group);
 		mutex_unlock(&group->mark_mutex);
 		fsnotify_put_mark(mark);
 	}
 }

 /*
  * Given a group, destroy all of the marks associated with that group.
  */
 void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
 {
 	fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
 }

 void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
 {
 	assert_spin_locked(&old->lock);
 	new->inode = old->inode;
 	new->mnt = old->mnt;
 	if (old->group)
 		fsnotify_get_group(old->group);
 	new->group = old->group;
 	new->mask = old->mask;
 	new->free_mark = old->free_mark;
 }

 /*
  * Nothing fancy, just initialize lists and locks and counters.
  */
 void fsnotify_init_mark(struct fsnotify_mark *mark,
 			void (*free_mark)(struct fsnotify_mark *mark))
 {
 	memset(mark, 0, sizeof(*mark));
 	spin_lock_init(&mark->lock);
 	atomic_set(&mark->refcnt, 1);
 	mark->free_mark = free_mark;
 }

 static int fsnotify_mark_destroy(void *ignored)
 {
 	struct fsnotify_mark *mark, *next;
 	struct list_head private_destroy_list;

 	for (;;) {
 		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_put_mark(mark);
 		}

 		wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
 	}

 	return 0;
 }

 static int __init fsnotify_mark_init(void)
 {
 	struct task_struct *thread;

 	thread = kthread_run(fsnotify_mark_destroy, NULL,
 			     "fsnotify_mark");
 	if (IS_ERR(thread))
 		panic("unable to start fsnotify mark destruction thread.");

 	return 0;
 }
 device_initcall(fsnotify_mark_init);
	/*
	* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2, or (at your option)
	* any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; see the file COPYING. If not, write to
	* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
	*/

	/*
	* 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
	* inode->i_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.
	*
	* inode->i_lock protects the i_fsnotify_marks list anchored inside a
	* given inode and each mark is hooked via the i_list. (and sorta the
	* free_i_list)
	*
	*
	* LIFETIME:
	* Inode marks survive between when they are added to an inode and when their
	* refcnt==0.
	*
	* 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)
	*
	* Worst case we are given an inode and need to clean up all the marks on that
	* inode. We take i_lock and walk the i_fsnotify_marks safely. For each
	* mark on the list we take a reference (so the mark can't disappear under us).
	* We remove that mark form the inode's list of marks and we add this mark to a
	* private list anchored on the stack using i_free_list; we walk i_free_list
	* and before we destroy the mark we make sure that we dont race with a
	* concurrent destroy_group by getting a ref to the marks group and taking the
	* groups mutex.

	* Very similarly for freeing by group, except we use free_g_list.
	*
	* 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/atomic.h>

	#include <linux/fsnotify_backend.h>
	#include "fsnotify.h"

	struct srcu_struct fsnotify_mark_srcu;
	static DEFINE_SPINLOCK(destroy_lock);
	static LIST_HEAD(destroy_list);
	static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);

	void fsnotify_get_mark(struct fsnotify_mark *mark)
	{
	atomic_inc(&mark->refcnt);
	}

	void fsnotify_put_mark(struct fsnotify_mark *mark)
	{
	if (atomic_dec_and_test(&mark->refcnt)) {
	if (mark->group)
	fsnotify_put_group(mark->group);
	mark->free_mark(mark);
	}
	}

	/* Calculate mask of events for a list of marks */
	u32 fsnotify_recalc_mask(struct hlist_head *head)
	{
	u32 new_mask = 0;
	struct fsnotify_mark *mark;

	hlist_for_each_entry(mark, head, obj_list)
	new_mask \|= mark->mask;
	return new_mask;
	}

	/*
	* Any time a mark is getting freed we end up here.
	* The caller had better be holding a reference to this mark so we don't actually
	* do the final put under the mark->lock
	*/
	void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
	struct fsnotify_group *group)
	{
	struct inode *inode = NULL;

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

	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;

	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
	inode = mark->inode;
	fsnotify_destroy_inode_mark(mark);
	} else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
	fsnotify_destroy_vfsmount_mark(mark);
	else
	BUG();

	list_del_init(&mark->g_list);

	spin_unlock(&mark->lock);

	if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
	iput(inode);
	/* release lock temporarily */
	mutex_unlock(&group->mark_mutex);

	spin_lock(&destroy_lock);
	list_add(&mark->g_list, &destroy_list);
	spin_unlock(&destroy_lock);
	wake_up(&destroy_waitq);
	/*
	* We don't necessarily have a ref on mark from caller so the above destroy
	* may have actually freed it, unless this group provides a 'freeing_mark'
	* function which must be holding a reference.
	*/

	/*
	* 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);

	/*
	* __fsnotify_update_child_dentry_flags(inode);
	*
	* I really want to call that, but we can't, we have no idea if the inode
	* still exists the second we drop the mark->lock.
	*
	* The next time an event arrive to this inode from one of it's children
	* __fsnotify_parent will see that the inode doesn't care about it's
	* children and will update all of these flags then. So really this
	* is just a lazy update (and could be a perf win...)
	*/

	atomic_dec(&group->num_marks);

	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
	}

	void fsnotify_destroy_mark(struct fsnotify_mark *mark,
	struct fsnotify_group *group)
	{
	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
	fsnotify_destroy_mark_locked(mark, group);
	mutex_unlock(&group->mark_mutex);
	}

	/*
	* Destroy all marks in the given list. The marks must be already detached from
	* the original inode / vfsmount.
	*/
	void fsnotify_destroy_marks(struct list_head *to_free)
	{
	struct fsnotify_mark mark, lmark;
	struct fsnotify_group *group;

	list_for_each_entry_safe(mark, lmark, to_free, free_list) {
	spin_lock(&mark->lock);
	fsnotify_get_group(mark->group);
	group = mark->group;
	spin_unlock(&mark->lock);

	fsnotify_destroy_mark(mark, group);
	fsnotify_put_mark(mark);
	fsnotify_put_group(group);
	}
	}

	void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
	{
	assert_spin_locked(&mark->lock);

	mark->mask = mask;

	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
	fsnotify_set_inode_mark_mask_locked(mark, mask);
	}

	void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
	{
	assert_spin_locked(&mark->lock);

	mark->ignored_mask = mask;
	}

	/*
	* 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;
	}

	/* Add mark into proper place in given list of marks */
	int fsnotify_add_mark_list(struct hlist_head head, struct fsnotify_mark mark,
	int allow_dups)
	{
	struct fsnotify_mark lmark, last = NULL;
	int cmp;

	/* is mark the first mark? */
	if (hlist_empty(head)) {
	hlist_add_head_rcu(&mark->obj_list, head);
	return 0;
	}

	/* should mark be in the middle of the current list? */
	hlist_for_each_entry(lmark, head, obj_list) {
	last = lmark;

	if ((lmark->group == mark->group) && !allow_dups)
	return -EEXIST;

	cmp = fsnotify_compare_groups(lmark->group, mark->group);
	if (cmp >= 0) {
	hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
	return 0;
	}
	}

	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);
	return 0;
	}

	/*
	* 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,
	struct fsnotify_group group, struct inode inode,
	struct vfsmount *mnt, int allow_dups)
	{
	int ret = 0;

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

	/*
	* LOCKING ORDER!!!!
	* group->mark_mutex
	* mark->lock
	* inode->i_lock
	*/
	spin_lock(&mark->lock);
	mark->flags \|= FSNOTIFY_MARK_FLAG_ALIVE;

	fsnotify_get_group(group);
	mark->group = group;
	list_add(&mark->g_list, &group->marks_list);
	atomic_inc(&group->num_marks);
	fsnotify_get_mark(mark); /* for i_list and g_list */

	if (inode) {
	ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
	if (ret)
	goto err;
	} else if (mnt) {
	ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
	if (ret)
	goto err;
	} else {
	BUG();
	}

	/* this will pin the object if appropriate */
	fsnotify_set_mark_mask_locked(mark, mark->mask);
	spin_unlock(&mark->lock);

	if (inode)
	__fsnotify_update_child_dentry_flags(inode);

	return ret;
	err:
	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
	list_del_init(&mark->g_list);
	fsnotify_put_group(group);
	mark->group = NULL;
	atomic_dec(&group->num_marks);

	spin_unlock(&mark->lock);

	spin_lock(&destroy_lock);
	list_add(&mark->g_list, &destroy_list);
	spin_unlock(&destroy_lock);
	wake_up(&destroy_waitq);

	return ret;
	}

	int fsnotify_add_mark(struct fsnotify_mark mark, struct fsnotify_group group,
	struct inode inode, struct vfsmount mnt, int allow_dups)
	{
	int ret;
	mutex_lock(&group->mark_mutex);
	ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
	mutex_unlock(&group->mark_mutex);
	return ret;
	}

	/*
	* 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(struct hlist_head head,
	struct fsnotify_group *group)
	{
	struct fsnotify_mark *mark;

	hlist_for_each_entry(mark, head, obj_list) {
	if (mark->group == group) {
	fsnotify_get_mark(mark);
	return mark;
	}
	}
	return NULL;
	}

	/*
	* clear any marks in a group in which mark->flags & flags is true
	*/
	void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
	unsigned int flags)
	{
	struct fsnotify_mark lmark, mark;
	LIST_HEAD(to_free);

	/*
	* 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 (mark->flags & flags)
	list_move(&mark->g_list, &to_free);
	}
	mutex_unlock(&group->mark_mutex);

	while (1) {
	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
	if (list_empty(&to_free)) {
	mutex_unlock(&group->mark_mutex);
	break;
	}
	mark = list_first_entry(&to_free, struct fsnotify_mark, g_list);
	fsnotify_get_mark(mark);
	fsnotify_destroy_mark_locked(mark, group);
	mutex_unlock(&group->mark_mutex);
	fsnotify_put_mark(mark);
	}
	}

	/*
	* Given a group, destroy all of the marks associated with that group.
	*/
	void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
	{
	fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
	}

	void fsnotify_duplicate_mark(struct fsnotify_mark new, struct fsnotify_mark old)
	{
	assert_spin_locked(&old->lock);
	new->inode = old->inode;
	new->mnt = old->mnt;
	if (old->group)
	fsnotify_get_group(old->group);
	new->group = old->group;
	new->mask = old->mask;
	new->free_mark = old->free_mark;
	}

	/*
	* Nothing fancy, just initialize lists and locks and counters.
	*/
	void fsnotify_init_mark(struct fsnotify_mark *mark,
	void (free_mark)(struct fsnotify_mark mark))
	{
	memset(mark, 0, sizeof(*mark));
	spin_lock_init(&mark->lock);
	atomic_set(&mark->refcnt, 1);
	mark->free_mark = free_mark;
	}

	static int fsnotify_mark_destroy(void *ignored)
	{
	struct fsnotify_mark mark, next;
	struct list_head private_destroy_list;

	for (;;) {
	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_put_mark(mark);
	}

	wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
	}

	return 0;
	}

	static int __init fsnotify_mark_init(void)
	{
	struct task_struct *thread;

	thread = kthread_run(fsnotify_mark_destroy, NULL,
	"fsnotify_mark");
	if (IS_ERR(thread))
	panic("unable to start fsnotify mark destruction thread.");

	return 0;
	}
	device_initcall(fsnotify_mark_init);