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 mntput_no_expire

------------[ cut here ]------------
WARNING: CPU: 1 PID: 4281 at fs/namespace.c:1225 mntput_no_expire+0x979/0xfe0 fs/namespace.c:1225
Modules linked in:
CPU: 1 PID: 4281 Comm: syz-executor.3 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:mntput_no_expire+0x979/0xfe0 fs/namespace.c:1225
Code: 04 00 00 48 8b 35 0f a4 dd 0b b9 01 00 00 00 bf 08 00 00 00 48 c7 c2 60 fe f0 8b e8 41 0d 72 ff e9 01 f9 ff ff e8 37 bf 9d ff <0f> 0b e9 b6 f8 ff ff e8 2b bf 9d ff 0f 0b e9 aa f8 ff ff e8 1f bf
RSP: 0018:ffffc9000388fd78 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888015df8000 RSI: ffffffff81db81a9 RDI: 0000000000000003
RBP: 0000000000000008 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff81db7a48 R11: 0000000000000000 R12: 0000000000000002
R13: ffff888019de1380 R14: dffffc0000000000 R15: ffffed10033bc27a
FS:  00005555555f0400(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555563e6848 CR3: 000000007f64c000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 mntput+0x67/0x90 fs/namespace.c:1288
 __fput+0x3ba/0x9d0 fs/file_table.c:333
 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: 0033:0x7f8b4ea3bd2b
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007fffd543b3b0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f8b4ea3bd2b
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007f8b4eb9d960 R08: 0000000000000000 R09: 00007fffd547d080
R10: 0000000000000000 R11: 0000000000000293 R12: 00000000000169e6
R13: 00007fffd543b4b0 R14: 00007fffd543b4d0 R15: 0000000000000032
 </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=11d1bd99f00000
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=14c96d96f00000