WARNING: bad unlock balance in ovl_workdir_create (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2c8a3fce Linux 4.14.218
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1120b3d8d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=80e596b8b0902d96
dashboard link: https://syzkaller.appspot.com/bug?extid=0afecbfd7bf0e8d8f4be

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0afecb...@syzkaller.appspotmail.com

=====================================
WARNING: bad unlock balance detected!
4.14.218-syzkaller #0 Not tainted
-------------------------------------
syz-executor.3/25169 is trying to release lock (sb_writers) at:
[<ffffffff87043f5f>] ovl_workdir_create.cold+0xeb/0xf7 syzkaller/managers/linux-4-14/kernel/fs/overlayfs/super.c:546
but there are no more locks to release!

other info that might help us debug this:
1 lock held by syz-executor.3/25169:
#0: (&type->s_umount_key#64/1){+.+.}, at: [<ffffffff818705e6>] alloc_super syzkaller/managers/linux-4-14/kernel/fs/super.c:251 [inline]
#0: (&type->s_umount_key#64/1){+.+.}, at: [<ffffffff818705e6>] sget_userns+0x556/0xc10 syzkaller/managers/linux-4-14/kernel/fs/super.c:516

stack backtrace:
CPU: 1 PID: 25169 Comm: syz-executor.3 Not tainted 4.14.218-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack syzkaller/managers/linux-4-14/kernel/lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x281 syzkaller/managers/linux-4-14/kernel/lib/dump_stack.c:58
print_unlock_imbalance_bug syzkaller/managers/linux-4-14/kernel/./include/trace/events/lock.h:58 [inline]
__lock_release syzkaller/managers/linux-4-14/kernel/kernel/locking/lockdep.c:3769 [inline]
lock_release.cold+0x70/0xbf syzkaller/managers/linux-4-14/kernel/kernel/locking/lockdep.c:4017
ovl_workdir_create.cold+0xeb/0xf7 syzkaller/managers/linux-4-14/kernel/fs/overlayfs/super.c:546
ovl_fill_super+0xfe9/0x2610 syzkaller/managers/linux-4-14/kernel/fs/overlayfs/super.c:988
mount_nodev+0x4c/0xf0 syzkaller/managers/linux-4-14/kernel/fs/super.c:1180
mount_fs+0x92/0x2a0 syzkaller/managers/linux-4-14/kernel/fs/super.c:1237
vfs_kern_mount.part.0+0x5b/0x470 syzkaller/managers/linux-4-14/kernel/fs/namespace.c:1046
vfs_kern_mount syzkaller/managers/linux-4-14/kernel/fs/namespace.c:1036 [inline]
do_new_mount syzkaller/managers/linux-4-14/kernel/fs/namespace.c:2549 [inline]
do_mount+0xe53/0x2a00 syzkaller/managers/linux-4-14/kernel/fs/namespace.c:2879
SYSC_mount syzkaller/managers/linux-4-14/kernel/fs/namespace.c:3095 [inline]
SyS_mount+0xa8/0x120 syzkaller/managers/linux-4-14/kernel/fs/namespace.c:3072
do_syscall_64+0x1d5/0x640 syzkaller/managers/linux-4-14/kernel/arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x465b09
RSP: 002b:00007fce684dd188 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000465b09
RDX: 00000000200000c0 RSI: 0000000020000000 RDI: 000000000040000d
RBP: 00000000004b069f R08: 0000000020000100 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60
R13: 00007fff33e86f0f R14: 00007fce684dd300 R15: 0000000000022000
overlayfs: failed to create directory ./file1\/work (errno: 30); mounting read-only
------------[ cut here ]------------
WARNING: CPU: 1 PID: 7998 at fs/namespace.c:1178 cleanup_mnt+0x222/0x2c0 syzkaller/managers/linux-4-14/kernel/fs/namespace.c:1178


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.