On Wed, 02 Mar 2022, Stefano Garzarella wrote:
On Wed, Mar 02, 2022 at 04:49:17PM +0000, Lee Jones wrote:
On Wed, 02 Mar 2022, Michael S. Tsirkin wrote:
On Wed, Mar 02, 2022 at 05:28:31PM +0100, Stefano Garzarella wrote:
On Wed, Mar 2, 2022 at 3:57 PM Lee Jones lee.jones@linaro.org wrote:
On Wed, 02 Mar 2022, Michael S. Tsirkin wrote:
On Wed, Mar 02, 2022 at 01:56:35PM +0000, Lee Jones wrote: > On Wed, 02 Mar 2022, Michael S. Tsirkin wrote: > > > On Wed, Mar 02, 2022 at 07:54:21AM +0000, Lee Jones wrote: > > > vhost_vsock_handle_tx_kick() already holds the mutex during its call > > > to vhost_get_vq_desc(). All we have to do is take the same lock > > > during virtqueue clean-up and we mitigate the reported issues. > > > > > > Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00 > > > > > > Cc: stable@vger.kernel.org > > > Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com > > > Signed-off-by: Lee Jones lee.jones@linaro.org > > > --- > > > drivers/vhost/vhost.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 59edb5a1ffe28..bbaff6a5e21b8 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -693,6 +693,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev) > > > int i; > > > > > > for (i = 0; i < dev->nvqs; ++i) { > > > + mutex_lock(&dev->vqs[i]->mutex); > > > if (dev->vqs[i]->error_ctx) > > > eventfd_ctx_put(dev->vqs[i]->error_ctx); > > > if (dev->vqs[i]->kick) > > > @@ -700,6 +701,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev) > > > if (dev->vqs[i]->call_ctx.ctx) > > > eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx); > > > vhost_vq_reset(dev, dev->vqs[i]); > > > + mutex_unlock(&dev->vqs[i]->mutex); > > > } > > > > So this is a mitigation plan but the bug is still there though > > we don't know exactly what it is. I would prefer adding something like > > WARN_ON(mutex_is_locked(vqs[i]->mutex) here - does this make sense? > > As a rework to this, or as a subsequent patch?
Can be a separate patch.
> Just before the first lock I assume?
I guess so, yes.
No problem. Patch to follow.
I'm also going to attempt to debug the root cause, but I'm new to this subsystem to it might take a while for me to get my head around.
IIUC the root cause should be the same as the one we solved here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
The worker was not stopped before calling vhost_dev_cleanup(). So while the worker was still running we were going to free memory or initialize fields while it was still using virtqueue.
Right, and I agree but it's not the root though, we do attempt to stop all workers.
Exactly. This is what happens, but the question I'm going to attempt to answer is *why* does this happen.
IIUC the worker was still running because the /dev/vhost-vsock file was not explicitly closed, so vhost_vsock_dev_release() was called in the do_exit() of the process.
In that case there was the issue, because vhost_dev_check_owner() returned false in vhost_vsock_stop() since current->mm was NULL. So it returned earlier, without calling vhost_vq_set_backend(vq, NULL).
This did not stop the worker from continuing to run, causing the multiple issues we are seeing.
current->mm was NULL, because in the do_exit() the address space is cleaned in the exit_mm(), which is called before releasing the files into the exit_task_work().
This can be seen from the logs, where we see first the warnings printed by vhost_dev_cleanup() and then the panic in the worker (e.g. here https://syzkaller.appspot.com/text?tag=CrashLog&x=16a61fce700000)
Mike also added a few more helpful details in this thread: https://lore.kernel.org/virtualization/20220221100500.2x3s2sddqahgdfyt@sgarz...
I guess that about sums it up. :)