![Miklos Szeredi](/assets/img/avatar_default.png)
Removing the parent of a watched file results in "kernel BUG at fs/notify/mark.c:139". To reproduce add "-w /tmp/audit/dir/watched_file" to audit.rules rm -rf /tmp/audit/dir This is caused by fsnotify_destroy_mark() being called without an extra reference taken by the caller. Reported by Francesco Cosoleto here: https://bugzilla.novell.com/show_bug.cgi?id=689860 Fix by removing the BUG_ON and adding a comment about not accessing mark after the iput. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> CC: stable@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
373 lines
11 KiB
C
373 lines
11 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 mark->refcnt tells how many "things" in the kernel currently are
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* referencing this object. The object typically will live inside the kernel
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* with a refcnt of 2, one for each list it is on (i_list, g_list). Any task
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* which can find this object holding the appropriete locks, can take a reference
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* and the 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 spinlocks involved with fsnotify inode marks and they MUST
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* be taken in order as follows:
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*
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* mark->lock
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* group->mark_lock
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* inode->i_lock
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*
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* mark->lock protects 2 things, mark->group and mark->inode. You must hold
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* that lock to dereference either of these things (they could be NULL even with
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* the lock)
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*
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* group->mark_lock protects the marks_list anchored inside a given group
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* and each mark is hooked via the g_list. It also sorta protects the
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* free_g_list, which when used is anchored by a private list on the stack of the
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* task which held the group->mark_lock.
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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; At this point we no
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* longer fear anything finding the mark using the inode's list of marks.
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*
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* We can safely and locklessly run the private list on the stack of everything
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* we just unattached from the original inode. For each mark on the private list
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* we grab the mark-> and can thus dereference mark->group and mark->inode. If
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* we see the group and inode are not NULL we take those locks. Now holding all
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* 3 locks we can completely remove the mark from other tasks finding it in the
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* future. Remember, 10 things might already be referencing this mark, but they
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* better be holding a ref. We drop our reference we took before we unhooked it
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* from the inode. When the ref hits 0 we can free the mark.
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*
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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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mark->free_mark(mark);
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}
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/*
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* Any time a mark is getting freed we end up here.
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* The caller had better be holding a reference to this mark so we don't actually
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* do the final put under the mark->lock
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*/
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void fsnotify_destroy_mark(struct fsnotify_mark *mark)
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{
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struct fsnotify_group *group;
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struct inode *inode = NULL;
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spin_lock(&mark->lock);
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group = mark->group;
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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_lock(&group->mark_lock);
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if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
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inode = mark->i.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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list_del_init(&mark->g_list);
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spin_unlock(&group->mark_lock);
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spin_unlock(&mark->lock);
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spin_lock(&destroy_lock);
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list_add(&mark->destroy_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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* __fsnotify_update_child_dentry_flags(inode);
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*
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* I really want to call that, but we can't, we have no idea if the inode
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* still exists the second we drop the mark->lock.
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*
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* The next time an event arrive to this inode from one of it's children
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* __fsnotify_parent will see that the inode doesn't care about it's
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* children and will update all of these flags then. So really this
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* is just a lazy update (and could be a perf win...)
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*/
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if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
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iput(inode);
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/*
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* We don't necessarily have a ref on mark from caller so the above iput
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* may have already destroyed it. Don't touch from now on.
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*/
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/*
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* it's possible that this group tried to destroy itself, but this
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* this mark was simultaneously being freed by inode. If that's the
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* case, we finish freeing the group here.
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*/
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if (unlikely(atomic_dec_and_test(&group->num_marks)))
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fsnotify_final_destroy_group(group);
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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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* 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(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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/*
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* LOCKING ORDER!!!!
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* mark->lock
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* group->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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spin_lock(&group->mark_lock);
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mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
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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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spin_unlock(&group->mark_lock);
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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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mark->group = NULL;
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atomic_dec(&group->num_marks);
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spin_unlock(&group->mark_lock);
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spin_unlock(&mark->lock);
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spin_lock(&destroy_lock);
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list_add(&mark->destroy_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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/*
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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(free_list);
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spin_lock(&group->mark_lock);
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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_add(&mark->free_g_list, &free_list);
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list_del_init(&mark->g_list);
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fsnotify_get_mark(mark);
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}
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}
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spin_unlock(&group->mark_lock);
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list_for_each_entry_safe(mark, lmark, &free_list, free_g_list) {
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fsnotify_destroy_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->i.inode = old->i.inode;
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new->m.mnt = old->m.mnt;
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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)
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{
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struct fsnotify_mark *mark, *next;
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LIST_HEAD(private_destroy_list);
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for (;;) {
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spin_lock(&destroy_lock);
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/* exchange the list head */
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list_replace_init(&destroy_list, &private_destroy_list);
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spin_unlock(&destroy_lock);
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synchronize_srcu(&fsnotify_mark_srcu);
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list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
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list_del_init(&mark->destroy_list);
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fsnotify_put_mark(mark);
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}
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wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
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}
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return 0;
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}
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static int __init fsnotify_mark_init(void)
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{
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struct task_struct *thread;
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thread = kthread_run(fsnotify_mark_destroy, NULL,
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"fsnotify_mark");
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if (IS_ERR(thread))
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panic("unable to start fsnotify mark destruction thread.");
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return 0;
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}
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device_initcall(fsnotify_mark_init);
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