On Wed, Mar 02, 2022 at 04:36:43PM +0100, Stefano Garzarella wrote: > On Wed, Mar 02, 2022 at 09:50:38AM -0500, Michael S. Tsirkin wrote: > > On Wed, Mar 02, 2022 at 03:11:21PM +0100, Stefano Garzarella wrote: > > > On Wed, Mar 02, 2022 at 08:35:08AM -0500, Michael S. Tsirkin wrote: > > > > On Wed, Mar 02, 2022 at 10:34:46AM +0100, Stefano Garzarella 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 > > > > > > > > > > This issue is similar to [1] that should be already fixed upstream by [2]. > > > > > > > > > > However I think this patch would have prevented some issues, because > > > > > vhost_vq_reset() sets vq->private to NULL, preventing the worker from > > > > > running. > > > > > > > > > > Anyway I think that when we enter in vhost_dev_cleanup() the worker should > > > > > be already stopped, so it shouldn't be necessary to take the mutex. But in > > > > > order to prevent future issues maybe it's better to take them, so: > > > > > > > > > > Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx> > > > > > > > > > > [1] > > > > > https://syzkaller.appspot.com/bug?id=993d8b5e64393ed9e6a70f9ae4de0119c605a822 > > > > > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a58da53ffd70294ebea8ecd0eb45fd0d74add9f9 > > > > > > > > > > > > Right. I want to queue this but I would like to get a warning > > > > so we can detect issues like [2] before they cause more issues. > > > > > > I agree, what about moving the warning that we already have higher up, right > > > at the beginning of the function? > > > > > > I mean something like this: > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 59edb5a1ffe2..1721ff3f18c0 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -692,6 +692,8 @@ void vhost_dev_cleanup(struct vhost_dev *dev) > > > { > > > int i; > > > + WARN_ON(!llist_empty(&dev->work_list)); > > > + > > > for (i = 0; i < dev->nvqs; ++i) { > > > if (dev->vqs[i]->error_ctx) > > > eventfd_ctx_put(dev->vqs[i]->error_ctx); > > > @@ -712,7 +714,6 @@ void vhost_dev_cleanup(struct vhost_dev *dev) > > > dev->iotlb = NULL; > > > vhost_clear_msg(dev); > > > wake_up_interruptible_poll(&dev->wait, EPOLLIN | EPOLLRDNORM); > > > - WARN_ON(!llist_empty(&dev->work_list)); > > > if (dev->worker) { > > > kthread_stop(dev->worker); > > > dev->worker = NULL; > > > > > > > Hmm I'm not sure why it matters. > > Because after this new patch, putting locks in the while loop, when we > finish the loop the workers should be stopped, because vhost_vq_reset() sets > vq->private to NULL. > > But the best thing IMHO is to check that there is no backend set for each > vq, so the workers have been stopped correctly at this point. > > Thanks, > Stefano It's the list of workers waiting to run though. That is not affected by vq lock at all. -- MST
