WARNING in cleanup_mnt (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bbf5c979 Linux 5.9
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15498ffb900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3d8333c88fe898d7
dashboard link: https://syzkaller.appspot.com/bug?extid=428c51fcb8f9e5a84850
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

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+428c51fcb8f9e5a84850@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
WARNING: CPU: 1 PID: 30737 at fs/namespace.c:1109 cleanup_mnt+0x409/0x530 fs/namespace.c:1109
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 30737 Comm: syz-executor.3 Not tainted 5.9.0-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+0x198/0x1fd lib/dump_stack.c:118
 panic+0x382/0x7fb kernel/panic.c:231
 __warn.cold+0x20/0x4b kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:cleanup_mnt+0x409/0x530 fs/namespace.c:1109
Code: 8a e8 9b c0 0c 02 49 8d 7c 24 38 48 c7 c6 80 4a ca 81 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 ec 9c 98 ff e8 f7 9f ab ff <0f> 0b e9 0a fd ff ff e8 eb 9f ab ff 4c 89 e7 e8 43 03 06 00 e9 2f
RSP: 0018:ffffc900163afac0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff81ca9c21
RDX: ffff88809201a2c0 RSI: ffffffff81ca9f19 RDI: 0000000000000005
RBP: 0000000000000040 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880889c0540
R13: 000000000000042b R14: 0000000000000007 R15: 0000000000000002
 task_work_run+0xdd/0x190 kernel/task_work.c:141
 exit_task_work include/linux/task_work.h:25 [inline]
 do_exit+0xb7d/0x29f0 kernel/exit.c:806
 do_group_exit+0x125/0x310 kernel/exit.c:903
 get_signal+0x428/0x1f00 kernel/signal.c:2757
 arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:267
 __do_fast_syscall_32+0x6c/0x90 arch/x86/entry/common.c:138
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f06549
Code: Bad RIP value.
RSP: 002b:00000000090bfbfc EFLAGS: 00000212 ORIG_RAX: 0000000000000006
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000000000
RDX: 0000000000000005 RSI: 0000000008bab680 RDI: 0000000008bab680
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


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