On Mon, Feb 21, 2022 at 11:33:11PM +0530, Anirudh Rayabharam wrote:

On Mon, Feb 21, 2022 at 05:44:20PM +0100, Stefano Garzarella wrote:

quoted

On Mon, Feb 21, 2022 at 09:44:39PM +0530, Anirudh Rayabharam wrote:

quoted

On Mon, Feb 21, 2022 at 02:59:30PM +0100, Stefano Garzarella wrote:

quoted

On Mon, Feb 21, 2022 at 12:49 PM Stefano Garzarella [off-list ref] wrote:

quoted

vhost_vsock_stop() calls vhost_dev_check_owner() to check the device
ownership. It expects current->mm to be valid.

vhost_vsock_stop() is also called by vhost_vsock_dev_release() when
the user has not done close(), so when we are in do_exit(). In this
case current->mm is invalid and we're releasing the device, so we
should clean it anyway.

Let's check the owner only when vhost_vsock_stop() is called
by an ioctl.

Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
Cc: stable@vger.kernel.org
Reported-by: syzbot+1e3ea63db39f2b4440e0@syzkaller.appspotmail.com
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 drivers/vhost/vsock.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Reported-and-tested-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com

I don't think this patch fixes "INFO: task hung in vhost_work_dev_flush"
even though syzbot says so. I am able to reproduce the issue locally
even with this patch applied.

Are you using the sysbot reproducer or another test?
In that case, can you share it?

I am using the syzbot reproducer.

quoted

From the stack trace it seemed to me that the worker accesses a zone that
has been cleaned (iotlb), so it is invalid and fails.

Would the thread hang in that case? How?

Looking at this log [1] it seems that the process is blocked on the 
wait_for_completion() in vhost_work_dev_flush().

Since we're not setting the backend to NULL to stop the worker, it's 
likely that the worker will keep running, preventing the flush work from 
completing.

[1] https://syzkaller.appspot.com/text?tag=CrashLog&x=153f0852700000