Re: [syzbot] WARNING in mntput_no_expire (3)

[syzbot <syzbot+5b1e53987f858500ec00@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in cleanup_mnt

------------[ cut here ]------------
WARNING: CPU: 1 PID: 4044 at fs/namespace.c:1177 cleanup_mnt+0x416/0x540 fs/namespace.c:1177
Modules linked in:

CPU: 1 PID: 4044 Comm: syz-executor.0 Not tainted 5.18.0-rc6-syzkaller-00009-gfeb9c5e19e91-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:cleanup_mnt+0x416/0x540 fs/namespace.c:1177
Code: 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 f1 9f 89 ff e8 5c b3 9d ff 48 89 df e8 84 52 06 00 e9 40 fd ff ff e8 4a b3 9d ff <0f> 0b e9 ff fc ff ff e8 2e 44 e9 ff eb ab 48 c7 c7 a0 26 b9 8d e8
RSP: 0018:ffffc900031efe78 EFLAGS: 00010293

RAX: 0000000000000000 RBX: ffff88814013dc80 RCX: 0000000000000000
RDX: ffff888073a85880 RSI: ffffffff81db8d96 RDI: 0000000000000003
RBP: 0000000000000008 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff81db8a93 R11: 0000000000000001 R12: 00000000ffffffff
R13: 0000000000000002 R14: dffffc0000000000 R15: ffffed1028027b9a
FS:  0000555556e94400(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4df11a0000 CR3: 000000007054d000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 task_work_run+0xdd/0x1a0 kernel/task_work.c:164
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:169 [inline]
 exit_to_user_mode_prepare+0x23c/0x250 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:294
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f832748a557
Code: ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc0b9d39f8 EFLAGS: 00000246
 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f832748a557
RDX: 00007ffc0b9d3ac9 RSI: 000000000000000a RDI: 00007ffc0b9d3ac0
RBP: 00007ffc0b9d3ac0 R08: 00000000ffffffff R09: 00007ffc0b9d3890
R10: 0000555556e958b3 R11: 0000000000000246 R12: 00007f83274e21f8
R13: 00007ffc0b9d4b80 R14: 0000555556e95810 R15: 00007ffc0b9d4bc0
 </TASK>


Tested on:

commit:         feb9c5e1 Merge tag 'for_linus' of git://git.kernel.org..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
console output: https://syzkaller.appspot.com/x/log.txt?x=17d119aef00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=79caa0035f59d385
dashboard link: https://syzkaller.appspot.com/bug?extid=5b1e53987f858500ec00
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12ab09a5f00000