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

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jeff Layton <jlayton@kernel.org>
Date: Thu, 06 Feb 2025 06:53:08 -0500
> 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@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 syzkaller@googlegroups.com.
> > 
> > syzbot will keep track of this issue. See:
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> > 
> > 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:
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> > 
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> > 
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> > 
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> 
> 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.

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().").


> 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.