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4712e722f9
fsnotify_destroy_mark_locked() is subtle to use because it temporarily releases group->mark_mutex. To avoid future problems with this function, split it into two. fsnotify_detach_mark() is the part that needs group->mark_mutex and fsnotify_free_mark() is the part that must be called outside of group->mark_mutex. This way it's much clearer what's going on and we also avoid some pointless acquisitions of group->mark_mutex. Signed-off-by: Jan Kara <jack@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
532 lines
15 KiB
C
532 lines
15 KiB
C
/*
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* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* fsnotify inode mark locking/lifetime/and refcnting
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*
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* REFCNT:
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* The group->recnt and mark->refcnt tell how many "things" in the kernel
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* currently are referencing the objects. Both kind of objects typically will
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* live inside the kernel with a refcnt of 2, one for its creation and one for
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* the reference a group and a mark hold to each other.
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* If you are holding the appropriate locks, you can take a reference and the
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* object itself is guaranteed to survive until the reference is dropped.
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*
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* LOCKING:
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* There are 3 locks involved with fsnotify inode marks and they MUST be taken
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* in order as follows:
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*
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* group->mark_mutex
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* mark->lock
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* inode->i_lock
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*
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* group->mark_mutex protects the marks_list anchored inside a given group and
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* each mark is hooked via the g_list. It also protects the groups private
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* data (i.e group limits).
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* mark->lock protects the marks attributes like its masks and flags.
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* Furthermore it protects the access to a reference of the group that the mark
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* is assigned to as well as the access to a reference of the inode/vfsmount
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* that is being watched by the mark.
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*
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* inode->i_lock protects the i_fsnotify_marks list anchored inside a
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* given inode and each mark is hooked via the i_list. (and sorta the
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* free_i_list)
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*
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*
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* LIFETIME:
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* Inode marks survive between when they are added to an inode and when their
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* refcnt==0.
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*
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* The inode mark can be cleared for a number of different reasons including:
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* - The inode is unlinked for the last time. (fsnotify_inode_remove)
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* - The inode is being evicted from cache. (fsnotify_inode_delete)
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* - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
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* - Something explicitly requests that it be removed. (fsnotify_destroy_mark)
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* - The fsnotify_group associated with the mark is going away and all such marks
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* need to be cleaned up. (fsnotify_clear_marks_by_group)
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*
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* Worst case we are given an inode and need to clean up all the marks on that
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* inode. We take i_lock and walk the i_fsnotify_marks safely. For each
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* mark on the list we take a reference (so the mark can't disappear under us).
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* We remove that mark form the inode's list of marks and we add this mark to a
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* private list anchored on the stack using i_free_list; we walk i_free_list
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* and before we destroy the mark we make sure that we dont race with a
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* concurrent destroy_group by getting a ref to the marks group and taking the
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* groups mutex.
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* Very similarly for freeing by group, except we use free_g_list.
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*
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* This has the very interesting property of being able to run concurrently with
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* any (or all) other directions.
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*/
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/kthread.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/srcu.h>
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#include <linux/atomic.h>
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#include <linux/fsnotify_backend.h>
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#include "fsnotify.h"
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struct srcu_struct fsnotify_mark_srcu;
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static DEFINE_SPINLOCK(destroy_lock);
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static LIST_HEAD(destroy_list);
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static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
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void fsnotify_get_mark(struct fsnotify_mark *mark)
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{
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atomic_inc(&mark->refcnt);
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}
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void fsnotify_put_mark(struct fsnotify_mark *mark)
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{
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if (atomic_dec_and_test(&mark->refcnt)) {
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if (mark->group)
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fsnotify_put_group(mark->group);
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mark->free_mark(mark);
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}
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}
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/* Calculate mask of events for a list of marks */
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u32 fsnotify_recalc_mask(struct hlist_head *head)
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{
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u32 new_mask = 0;
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struct fsnotify_mark *mark;
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hlist_for_each_entry(mark, head, obj_list)
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new_mask |= mark->mask;
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return new_mask;
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}
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/*
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* Remove mark from inode / vfsmount list, group list, drop inode reference
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* if we got one.
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*
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* Must be called with group->mark_mutex held.
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*/
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void fsnotify_detach_mark(struct fsnotify_mark *mark)
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{
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struct inode *inode = NULL;
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struct fsnotify_group *group = mark->group;
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BUG_ON(!mutex_is_locked(&group->mark_mutex));
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spin_lock(&mark->lock);
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/* something else already called this function on this mark */
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if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
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spin_unlock(&mark->lock);
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return;
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}
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mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
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if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
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inode = mark->inode;
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fsnotify_destroy_inode_mark(mark);
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} else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
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fsnotify_destroy_vfsmount_mark(mark);
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else
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BUG();
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/*
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* Note that we didn't update flags telling whether inode cares about
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* what's happening with children. We update these flags from
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* __fsnotify_parent() lazily when next event happens on one of our
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* children.
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*/
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list_del_init(&mark->g_list);
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spin_unlock(&mark->lock);
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if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
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iput(inode);
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atomic_dec(&group->num_marks);
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}
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/*
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* Free fsnotify mark. The freeing is actually happening from a kthread which
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* first waits for srcu period end. Caller must have a reference to the mark
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* or be protected by fsnotify_mark_srcu.
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*/
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void fsnotify_free_mark(struct fsnotify_mark *mark)
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{
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struct fsnotify_group *group = mark->group;
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spin_lock(&mark->lock);
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/* something else already called this function on this mark */
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if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
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spin_unlock(&mark->lock);
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return;
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}
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mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
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spin_unlock(&mark->lock);
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spin_lock(&destroy_lock);
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list_add(&mark->g_list, &destroy_list);
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spin_unlock(&destroy_lock);
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wake_up(&destroy_waitq);
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/*
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* Some groups like to know that marks are being freed. This is a
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* callback to the group function to let it know that this mark
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* is being freed.
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*/
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if (group->ops->freeing_mark)
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group->ops->freeing_mark(mark, group);
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}
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void fsnotify_destroy_mark(struct fsnotify_mark *mark,
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struct fsnotify_group *group)
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{
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mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
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fsnotify_detach_mark(mark);
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mutex_unlock(&group->mark_mutex);
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fsnotify_free_mark(mark);
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}
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void fsnotify_destroy_marks(struct hlist_head *head, spinlock_t *lock)
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{
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struct fsnotify_mark *mark;
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while (1) {
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/*
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* We have to be careful since we can race with e.g.
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* fsnotify_clear_marks_by_group() and once we drop 'lock',
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* mark can get removed from the obj_list and destroyed. But
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* we are holding mark reference so mark cannot be freed and
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* calling fsnotify_destroy_mark() more than once is fine.
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*/
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spin_lock(lock);
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if (hlist_empty(head)) {
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spin_unlock(lock);
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break;
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}
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mark = hlist_entry(head->first, struct fsnotify_mark, obj_list);
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/*
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* We don't update i_fsnotify_mask / mnt_fsnotify_mask here
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* since inode / mount is going away anyway. So just remove
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* mark from the list.
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*/
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hlist_del_init_rcu(&mark->obj_list);
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fsnotify_get_mark(mark);
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spin_unlock(lock);
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fsnotify_destroy_mark(mark, mark->group);
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fsnotify_put_mark(mark);
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}
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}
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void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
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{
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assert_spin_locked(&mark->lock);
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mark->mask = mask;
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if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
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fsnotify_set_inode_mark_mask_locked(mark, mask);
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}
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void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
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{
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assert_spin_locked(&mark->lock);
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mark->ignored_mask = mask;
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}
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/*
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* Sorting function for lists of fsnotify marks.
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*
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* Fanotify supports different notification classes (reflected as priority of
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* notification group). Events shall be passed to notification groups in
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* decreasing priority order. To achieve this marks in notification lists for
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* inodes and vfsmounts are sorted so that priorities of corresponding groups
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* are descending.
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*
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* Furthermore correct handling of the ignore mask requires processing inode
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* and vfsmount marks of each group together. Using the group address as
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* further sort criterion provides a unique sorting order and thus we can
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* merge inode and vfsmount lists of marks in linear time and find groups
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* present in both lists.
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*
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* A return value of 1 signifies that b has priority over a.
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* A return value of 0 signifies that the two marks have to be handled together.
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* A return value of -1 signifies that a has priority over b.
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*/
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int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
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{
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if (a == b)
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return 0;
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if (!a)
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return 1;
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if (!b)
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return -1;
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if (a->priority < b->priority)
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return 1;
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if (a->priority > b->priority)
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return -1;
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if (a < b)
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return 1;
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return -1;
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}
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/* Add mark into proper place in given list of marks */
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int fsnotify_add_mark_list(struct hlist_head *head, struct fsnotify_mark *mark,
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int allow_dups)
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{
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struct fsnotify_mark *lmark, *last = NULL;
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int cmp;
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/* is mark the first mark? */
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if (hlist_empty(head)) {
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hlist_add_head_rcu(&mark->obj_list, head);
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return 0;
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}
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/* should mark be in the middle of the current list? */
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hlist_for_each_entry(lmark, head, obj_list) {
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last = lmark;
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if ((lmark->group == mark->group) && !allow_dups)
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return -EEXIST;
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cmp = fsnotify_compare_groups(lmark->group, mark->group);
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if (cmp >= 0) {
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hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
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return 0;
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}
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}
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BUG_ON(last == NULL);
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/* mark should be the last entry. last is the current last entry */
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hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
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return 0;
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}
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/*
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* Attach an initialized mark to a given group and fs object.
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* These marks may be used for the fsnotify backend to determine which
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* event types should be delivered to which group.
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*/
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int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
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struct fsnotify_group *group, struct inode *inode,
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struct vfsmount *mnt, int allow_dups)
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{
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int ret = 0;
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BUG_ON(inode && mnt);
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BUG_ON(!inode && !mnt);
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BUG_ON(!mutex_is_locked(&group->mark_mutex));
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/*
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* LOCKING ORDER!!!!
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* group->mark_mutex
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* mark->lock
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* inode->i_lock
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*/
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spin_lock(&mark->lock);
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mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
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fsnotify_get_group(group);
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mark->group = group;
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list_add(&mark->g_list, &group->marks_list);
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atomic_inc(&group->num_marks);
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fsnotify_get_mark(mark); /* for i_list and g_list */
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if (inode) {
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ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
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if (ret)
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goto err;
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} else if (mnt) {
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ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
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if (ret)
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goto err;
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} else {
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BUG();
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}
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/* this will pin the object if appropriate */
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fsnotify_set_mark_mask_locked(mark, mark->mask);
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spin_unlock(&mark->lock);
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if (inode)
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__fsnotify_update_child_dentry_flags(inode);
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return ret;
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err:
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mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
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list_del_init(&mark->g_list);
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fsnotify_put_group(group);
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mark->group = NULL;
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atomic_dec(&group->num_marks);
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spin_unlock(&mark->lock);
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spin_lock(&destroy_lock);
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list_add(&mark->g_list, &destroy_list);
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spin_unlock(&destroy_lock);
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wake_up(&destroy_waitq);
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return ret;
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}
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int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
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struct inode *inode, struct vfsmount *mnt, int allow_dups)
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{
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int ret;
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mutex_lock(&group->mark_mutex);
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ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
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mutex_unlock(&group->mark_mutex);
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return ret;
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}
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/*
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* Given a list of marks, find the mark associated with given group. If found
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* take a reference to that mark and return it, else return NULL.
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*/
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struct fsnotify_mark *fsnotify_find_mark(struct hlist_head *head,
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struct fsnotify_group *group)
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{
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struct fsnotify_mark *mark;
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hlist_for_each_entry(mark, head, obj_list) {
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if (mark->group == group) {
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fsnotify_get_mark(mark);
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return mark;
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}
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}
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return NULL;
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}
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/*
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* clear any marks in a group in which mark->flags & flags is true
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*/
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void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
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unsigned int flags)
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{
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struct fsnotify_mark *lmark, *mark;
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LIST_HEAD(to_free);
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/*
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* We have to be really careful here. Anytime we drop mark_mutex, e.g.
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* fsnotify_clear_marks_by_inode() can come and free marks. Even in our
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* to_free list so we have to use mark_mutex even when accessing that
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* list. And freeing mark requires us to drop mark_mutex. So we can
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* reliably free only the first mark in the list. That's why we first
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* move marks to free to to_free list in one go and then free marks in
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* to_free list one by one.
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*/
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mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
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list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
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if (mark->flags & flags)
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list_move(&mark->g_list, &to_free);
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}
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mutex_unlock(&group->mark_mutex);
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while (1) {
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mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
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if (list_empty(&to_free)) {
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mutex_unlock(&group->mark_mutex);
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break;
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}
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mark = list_first_entry(&to_free, struct fsnotify_mark, g_list);
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fsnotify_get_mark(mark);
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fsnotify_detach_mark(mark);
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mutex_unlock(&group->mark_mutex);
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fsnotify_free_mark(mark);
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fsnotify_put_mark(mark);
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}
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}
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/*
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* Given a group, destroy all of the marks associated with that group.
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*/
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void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
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{
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fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
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}
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void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
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{
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assert_spin_locked(&old->lock);
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new->inode = old->inode;
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new->mnt = old->mnt;
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if (old->group)
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fsnotify_get_group(old->group);
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new->group = old->group;
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new->mask = old->mask;
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new->free_mark = old->free_mark;
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}
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/*
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* Nothing fancy, just initialize lists and locks and counters.
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*/
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void fsnotify_init_mark(struct fsnotify_mark *mark,
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void (*free_mark)(struct fsnotify_mark *mark))
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{
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memset(mark, 0, sizeof(*mark));
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spin_lock_init(&mark->lock);
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atomic_set(&mark->refcnt, 1);
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mark->free_mark = free_mark;
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}
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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);
|