WARNING: bad unlock balance in ovl_llseek

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f8788d86 Linux 5.6-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13c5f8f9e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5d2e033af114153f
dashboard link: https://syzkaller.appspot.com/bug?extid=66a9752fa927f745385e
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=131d9a81e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14117a81e00000

The bug was bisected to:

commit b1f9d3858f724ed45b279b689fb5b400d91352e3
Author: Amir Goldstein <amir73il@xxxxxxxxx>
Date:   Sat Dec 21 09:42:29 2019 +0000

    ovl: use ovl_inode_lock in ovl_llseek()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16ff3bede00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=15ff3bede00000
console output: https://syzkaller.appspot.com/x/log.txt?x=11ff3bede00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+66a9752fa927f745385e@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: b1f9d3858f72 ("ovl: use ovl_inode_lock in ovl_llseek()")

=====================================
WARNING: bad unlock balance detected!
5.6.0-rc3-syzkaller #0 Not tainted
-------------------------------------
syz-executor194/8947 is trying to release lock (&ovl_i_lock_key[depth]) at:
[<ffffffff828b7835>] ovl_inode_unlock fs/overlayfs/overlayfs.h:328 [inline]
[<ffffffff828b7835>] ovl_llseek+0x215/0x2c0 fs/overlayfs/file.c:193
but there are no more locks to release!

other info that might help us debug this:
1 lock held by syz-executor194/8947:
 #0: ffff88809742ade0 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x279/0x310 fs/file.c:821

stack backtrace:
CPU: 0 PID: 8947 Comm: syz-executor194 Not tainted 5.6.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fb/0x318 lib/dump_stack.c:118
 print_unlock_imbalance_bug+0x20b/0x240 kernel/locking/lockdep.c:4007
 __lock_release kernel/locking/lockdep.c:4241 [inline]
 lock_release+0x469/0x710 kernel/locking/lockdep.c:4502
 __mutex_unlock_slowpath+0x80/0x5b0 kernel/locking/mutex.c:1228
 mutex_unlock+0xd/0x10 kernel/locking/mutex.c:740
 ovl_inode_unlock fs/overlayfs/overlayfs.h:328 [inline]
 ovl_llseek+0x215/0x2c0 fs/overlayfs/file.c:193
 vfs_llseek fs/read_write.c:300 [inline]
 ksys_lseek fs/read_write.c:313 [inline]
 __do_sys_lseek fs/read_write.c:324 [inline]
 __se_sys_lseek fs/read_write.c:322 [inline]
 __x64_sys_lseek+0x15f/0x1f0 fs/read_write.c:322
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x445df9
Code: e8 ac b8 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ff735aecce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000008
RAX: ffffffffffffffda RBX: 00000000006dac38 RCX: 0000000000445df


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
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