netdev - Re: [syzbot] [nfs?] [net?] WARNING in remove_proc

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Message-ID: <ca9c66778d4d777a3f3028d865b9f340553df72f.camel@kernel.org>
Date: Thu, 06 Feb 2025 06:53:08 -0500
From: Jeff Layton <jlayton@...nel.org>
To: syzbot <syzbot+e34ad04f27991521104c@...kaller.appspotmail.com>, 
	Dai.Ngo@...cle.com, chuck.lever@...cle.com, linux-kernel@...r.kernel.org, 
	linux-nfs@...r.kernel.org, neilb@...e.de, netdev@...r.kernel.org, 
	okorniev@...hat.com, syzkaller-bugs@...glegroups.com, tom@...pey.com
Subject: Re: [syzbot] [nfs?] [net?] WARNING in remove_proc_entry (7)

On Thu, 2025-02-06 at 00:38 -0800, syzbot wrote:
> 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+e34ad04f27991521104c@...kaller.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 syzkaller@...glegroups.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

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 <jlayton@...nel.org>