linux-kernel - Re: [syzbot] WARNING in mntput_no

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Message-ID: <0000000000004d422905dee62081@google.com>
Date:   Fri, 13 May 2022 08:14:09 -0700
From:   syzbot <syzbot+5b1e53987f858500ec00@...kaller.appspotmail.com>
To:     hdanton@...a.com, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] WARNING in mntput_no_expire (3)

Hello,

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

------------[ cut here ]------------
WARNING: CPU: 0 PID: 4063 at fs/namespace.c:1232 mntput_no_expire+0xb02/0xfe0 fs/namespace.c:1232
Modules linked in:
CPU: 0 PID: 4063 Comm: syz-executor.4 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+0xb02/0xfe0 fs/namespace.c:1232
Code: 00 48 c7 c7 80 16 db 89 c6 05 c3 c9 c8 0b 01 e8 19 58 4d 07 e9 57 ff ff ff e8 2a bf 9d ff 0f 0b e9 df f9 ff ff e8 1e bf 9d ff <0f> 0b e9 d3 f9 ff ff e8 12 bf 9d ff e8 9d b9 88 ff 31 ff 89 c3 89
RSP: 0018:ffffc9000335fc38 EFLAGS: 00010293

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88806e651d80 RSI: ffffffff81db81c2 RDI: 0000000000000003
RBP: 0000000000000008 R08: 0000000000000000 R09: ffffffff9006e94f
R10: ffffffff81db7b7e R11: 0000000000000001 R12: ffffc9000335fc88
R13: ffff88801a842300 R14: 0000000000000002 R15: dffffc0000000000
FS:  0000555557159400(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f18cda11280 CR3: 0000000077f04000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 mntput fs/namespace.c:1288 [inline]
 namespace_unlock+0x3ee/0x410 fs/namespace.c:1507
 do_umount fs/namespace.c:1726 [inline]
 path_umount+0x797/0x1260 fs/namespace.c:1808
 ksys_umount fs/namespace.c:1831 [inline]
 __do_sys_umount fs/namespace.c:1836 [inline]
 __se_sys_umount fs/namespace.c:1834 [inline]
 __x64_sys_umount+0x159/0x180 fs/namespace.c:1834
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7ff9a7c8a557
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:00007ffe33a40f28 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff9a7c8a557
RDX: 00007ffe33a40ff9 RSI: 000000000000000a RDI: 00007ffe33a40ff0
RBP: 00007ffe33a40ff0 R08: 00000000ffffffff R09: 00007ffe33a40dc0
R10: 000055555715a8b3 R11: 0000000000000246 R12: 00007ff9a7ce21f8
R13: 00007ffe33a420b0 R14: 000055555715a810 R15: 00007ffe33a420f0
 </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=14be78aef00000
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=10db8f71f00000