[syzbot] [nfs?] [net?] WARNING in remove_proc_entry (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 92514ef226f5 Merge tag 'for-6.14-rc1-tag' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=151e9318580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c48f582603dcb16c
dashboard link: https://syzkaller.appspot.com/bug?extid=e34ad04f27991521104c
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=131e9318580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b3df3b128344/disk-92514ef2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/30f6f3763191/vmlinux-92514ef2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/caeb03ac3f9c/bzImage-92514ef2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e34ad0...@syzkaller.appspotmail.com

name 'nfsd'
WARNING: CPU: 1 PID: 6518 at fs/proc/generic.c:713 remove_proc_entry+0x268/0x470 fs/proc/generic.c:713
Modules linked in:
CPU: 1 UID: 0 PID: 6518 Comm: kworker/u8:8 Not tainted 6.14.0-rc1-syzkaller-00034-g92514ef226f5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Workqueue: netns cleanup_net
RIP: 0010:remove_proc_entry+0x268/0x470 fs/proc/generic.c:713
Code: 08 eb a2 e8 1a 9c 62 ff 48 c7 c7 20 7e 41 8e e8 4e c4 f2 08 e8 09 9c 62 ff 90 48 c7 c7 c0 db 81 8b 4c 89 e6 e8 29 76 23 ff 90 <0f> 0b 90 90 e9 72 ff ff ff e8 ea 9b 62 ff 49 8d be 98 00 00 00 48
RSP: 0018:ffffc9000bec7a80 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 1ffff920017d8f52 RCX: ffffffff8179c889
RDX: ffff888031a35a00 RSI: ffffffff8179c896 RDI: 0000000000000001
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 00000000000ca440 R12: ffffffff8b8f7460
R13: dffffc0000000000 R14: ffff88807e22da00 R15: fffffbfff1cb7dc4
FS: 0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000237ba000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
nfsd_net_exit+0x27/0x50 fs/nfsd/nfsctl.c:2259
ops_exit_list+0xb0/0x180 net/core/net_namespace.c:172
cleanup_net+0x5c6/0xbf0 net/core/net_namespace.c:652
process_one_work+0x958/0x1b30 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3317 [inline]
worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
kthread+0x3af/0x750 kernel/kthread.c:464
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Jeff Layton]

Thanks for the bug report. That warning pops if you try to remove a
/proc entry and it doesn't exist.

My suspicion here is that the initial creation of that entry failed for
some reason and the nfsd code just ignored that error. In fact,
nfsd_proc_stat_init() ignores the return code from svc_proc_register().
If we fix that, then this probably would have failed gracefully at
net_init time. I'll see about spinning up a patch to fix that.

Cheers,
--
Jeff Layton <jla...@kernel.org>

[Kuniyuki Iwashima]

From: Jeff Layton <jla...@kernel.org>
Date: Thu, 06 Feb 2025 06:53:08 -0500

This failure is common and triggered by fault injection during netns
initialisation. You can see that in the syzbot's log:

https://syzkaller.appspot.com/x/log.txt?x=151e9318580000

I fixed a similar one in 24457f1be29f ("nfs: Handle error of
rpc_proc_register() in nfs_net_init().").