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@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx> > > > > > > > > > Reported-by: syzbot+adc3cb32385586bec859@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx> > > > > > > > > > --- > > > > > > > > > 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/?id=a58da53ffd70294ebea8ecd0eb45fd0d74add9f9 > > > > > > > > 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@sgarzare-redhat/T/#ree61316eac63245c9ba3050b44330e4034282cc2 I guess that about sums it up. :) -- Lee Jones [李琼斯] Principal Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog
