linux-kernel - [PATCH] inotify: Fix possible deadlock in fsnotify_destroy

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Message-ID: <20240927091231.360334-1-lizhi.xu@windriver.com>
Date: Fri, 27 Sep 2024 17:12:31 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <syzbot+c679f13773f295d2da53@...kaller.appspotmail.com>
CC: <amir73il@...il.com>, <jack@...e.cz>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <phillip@...ashfs.org.uk>,
        <squashfs-devel@...ts.sourceforge.net>,
        <syzkaller-bugs@...glegroups.com>
Subject: [PATCH] inotify: Fix possible deadlock in fsnotify_destroy_mark

[Syzbot reported]
WARNING: possible circular locking dependency detected
6.11.0-rc4-syzkaller-00019-gb311c1b497e5 #0 Not tainted
------------------------------------------------------
kswapd0/78 is trying to acquire lock:
ffff88801b8d8930 (&group->mark_mutex){+.+.}-{3:3}, at: fsnotify_group_lock include/linux/fsnotify_backend.h:270 [inline]
ffff88801b8d8930 (&group->mark_mutex){+.+.}-{3:3}, at: fsnotify_destroy_mark+0x38/0x3c0 fs/notify/mark.c:578

but task is already holding lock:
ffffffff8ea2fd60 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:6841 [inline]
ffffffff8ea2fd60 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0xbb4/0x35a0 mm/vmscan.c:7223

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
       __fs_reclaim_acquire mm/page_alloc.c:3818 [inline]
       fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3832
       might_alloc include/linux/sched/mm.h:334 [inline]
       slab_pre_alloc_hook mm/slub.c:3939 [inline]
       slab_alloc_node mm/slub.c:4017 [inline]
       kmem_cache_alloc_noprof+0x3d/0x2a0 mm/slub.c:4044
       inotify_new_watch fs/notify/inotify/inotify_user.c:599 [inline]
       inotify_update_watch fs/notify/inotify/inotify_user.c:647 [inline]
       __do_sys_inotify_add_watch fs/notify/inotify/inotify_user.c:786 [inline]
       __se_sys_inotify_add_watch+0x72e/0x1070 fs/notify/inotify/inotify_user.c:729
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&group->mark_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3133 [inline]
       check_prevs_add kernel/locking/lockdep.c:3252 [inline]
       validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3868
       __lock_acquire+0x137a/0x2040 kernel/locking/lockdep.c:5142
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
       fsnotify_group_lock include/linux/fsnotify_backend.h:270 [inline]
       fsnotify_destroy_mark+0x38/0x3c0 fs/notify/mark.c:578
       fsnotify_destroy_marks+0x14a/0x660 fs/notify/mark.c:934
       fsnotify_inoderemove include/linux/fsnotify.h:264 [inline]
       dentry_unlink_inode+0x2e0/0x430 fs/dcache.c:403
       __dentry_kill+0x20d/0x630 fs/dcache.c:610
       shrink_kill+0xa9/0x2c0 fs/dcache.c:1055
       shrink_dentry_list+0x2c0/0x5b0 fs/dcache.c:1082
       prune_dcache_sb+0x10f/0x180 fs/dcache.c:1163
       super_cache_scan+0x34f/0x4b0 fs/super.c:221
       do_shrink_slab+0x701/0x1160 mm/shrinker.c:435
       shrink_slab+0x1093/0x14d0 mm/shrinker.c:662
       shrink_one+0x43b/0x850 mm/vmscan.c:4815
       shrink_many mm/vmscan.c:4876 [inline]
       lru_gen_shrink_node mm/vmscan.c:4954 [inline]
       shrink_node+0x3799/0x3de0 mm/vmscan.c:5934
       kswapd_shrink_node mm/vmscan.c:6762 [inline]
       balance_pgdat mm/vmscan.c:6954 [inline]
       kswapd+0x1bcd/0x35a0 mm/vmscan.c:7223
       kthread+0x2f0/0x390 kernel/kthread.c:389
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(fs_reclaim);
                               lock(&group->mark_mutex);
                               lock(fs_reclaim);
  lock(&group->mark_mutex);

 *** DEADLOCK ***

[Analysis] 
The inotify_new_watch() call passes through GFP_KERNEL, use memalloc_nofs_save/
memalloc_nofs_restore to make sure we don't end up with the fs reclaim dependency.

Reported-and-tested-by: syzbot+c679f13773f295d2da53@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c679f13773f295d2da53
Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
---
 fs/notify/inotify/inotify_user.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index c7e451d5bd51..70b77b6186a6 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -643,8 +643,13 @@ static int inotify_update_watch(struct fsnotify_group *group, struct inode *inod
 	/* try to update and existing watch with the new arg */
 	ret = inotify_update_existing_watch(group, inode, arg);
 	/* no mark present, try to add a new one */
-	if (ret == -ENOENT)
+	if (ret == -ENOENT) {
+		unsigned int nofs_flag;
+
+		nofs_flag = memalloc_nofs_save();
 		ret = inotify_new_watch(group, inode, arg);
+		memalloc_nofs_restore(nofs_flag);
+	}
 	fsnotify_group_unlock(group);
 
 	return ret;
-- 
2.43.0