Subject: Re: [syzbot] WARNING in vhost_dev_cleanup (2)

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 17 Feb 2022 02:36:21 -0500

On Thu, Feb 17, 2022 at 03:34:13PM +0800, Jason Wang wrote:
> On Thu, Feb 17, 2022 at 10:01 AM syzbot
> <[email-masked]> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    c5d9ae265b10 Merge tag 'for-linus' of git://git.kernel.org..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=132e687c700000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=a78b064590b9f912
> > dashboard link: https://syzkaller.appspot.com/bug?extid=1e3ea63db39f2b4440e0
> > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: [email-masked]
> >
> > WARNING: CPU: 1 PID: 10828 at drivers/vhost/vhost.c:715 vhost_dev_cleanup+0x8b8/0xbc0 drivers/vhost/vhost.c:715
> > Modules linked in:
> > CPU: 0 PID: 10828 Comm: syz-executor.0 Not tainted 5.17.0-rc4-syzkaller-00051-gc5d9ae265b10 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > RIP: 0010:vhost_dev_cleanup+0x8b8/0xbc0 drivers/vhost/vhost.c:715
> 
> Probably a hint that we are missing a flush.
> 
> Looking at vhost_vsock_stop() that is called by vhost_vsock_dev_release():
> 
> static int vhost_vsock_stop(struct vhost_vsock *vsock)
> {
> size_t i;
>         int ret;
> 
>         mutex_lock(&vsock->dev.mutex);
> 
>         ret = vhost_dev_check_owner(&vsock->dev);
>         if (ret)
>                 goto err;
> 
> Where it could fail so the device is not actually stopped.
> 
> I wonder if this is something related.
> 
> Thanks

But then if that is not the owner then no work should be running, right?

> 
> > Code: c7 85 90 01 00 00 00 00 00 00 e8 53 6e a2 fa 48 89 ef 48 83 c4 20 5b 5d 41 5c 41 5d 41 5e 41 5f e9 7d d6 ff ff e8 38 6e a2 fa <0f> 0b e9 46 ff ff ff 48 8b 7c 24 10 e8 87 00 ea fa e9 75 f7 ff ff
> > RSP: 0018:ffffc9000fe6fa18 EFLAGS: 00010293
> > RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> > RDX: ffff888021b63a00 RSI: ffffffff86d66fe8 RDI: ffff88801cc200b0
> > RBP: ffff88801cc20000 R08: 0000000000000001 R09: 0000000000000001
> > R10: ffffffff817f1e08 R11: 0000000000000000 R12: ffff88801cc200d0
> > R13: ffff88801cc20120 R14: ffff88801cc200d0 R15: 0000000000000002
> > FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000001b2de25000 CR3: 000000004c9cd000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  <TASK>
> >  vhost_vsock_dev_release+0x36e/0x4b0 drivers/vhost/vsock.c:771
> >  __fput+0x286/0x9f0 fs/file_table.c:313
> >  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
> >  exit_task_work include/linux/task_work.h:32 [inline]
> >  do_exit+0xb29/0x2a30 kernel/exit.c:806
> >  do_group_exit+0xd2/0x2f0 kernel/exit.c:935
> >  get_signal+0x45a/0x2490 kernel/signal.c:2863
> >  arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:868
> >  handle_signal_work kernel/entry/common.c:148 [inline]
> >  exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
> >  exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:207
> >  __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
> >  syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
> >  do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
> >  entry_SYSCALL_64_after_hwframe+0x44/0xae
> > RIP: 0033:0x7f4027a46481
> > Code: Unable to access opcode bytes at RIP 0x7f4027a46457.
> > RSP: 002b:00007f402808ba68 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
> > RAX: fffffffffffffffc RBX: 00007f402622e700 RCX: 00007f4027a46481
> > RDX: 00007f402622e9d0 RSI: 00007f402622e2f0 RDI: 00000000003d0f00
> > RBP: 00007f402808bcb0 R08: 00007f402622e700 R09: 00007f402622e700
> > R10: 00007f402622e9d0 R11: 0000000000000206 R12: 00007f402808bb1e
> > R13: 00007f402808bb1f R14: 00007f402622e300 R15: 0000000000022000
> >  </TASK>
> >
> >
> > ---
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> > syzbot engineers can be reached at [email-masked].
> >
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> >