On Thu, Mar 03, 2022 at 04:01:06PM -0500, Michael S. Tsirkin wrote:
On Thu, Mar 03, 2022 at 09:14:36PM +0200, Leon Romanovsky wrote:
On Thu, Mar 03, 2022 at 03:19:29PM +0000, Lee Jones wrote:
> All workers/users should be halted before any clean-up should take place.
>
> Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> ---
> drivers/vhost/vhost.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index bbaff6a5e21b8..d935d2506963f 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -693,6 +693,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> int i;
>
> for (i = 0; i < dev->nvqs; ++i) {
> + /* Ideally all workers should be stopped prior to clean-up */
> + WARN_ON(mutex_is_locked(&dev->vqs[i]->mutex));
> +
> mutex_lock(&dev->vqs[i]->mutex);
I know nothing about vhost, but this construction and patch looks
strange to me.
If all workers were stopped, you won't need mutex_lock(). The mutex_lock
here suggests to me that workers can still run here.
Thanks
"Ideally" here is misleading, we need a bigger detailed comment
along the lines of:
/*
* By design, no workers can run here. But if there's a bug and the
* driver did not flush all work properly then they might, and we
* encountered such bugs in the past. With no proper flush guest won't
* work correctly but avoiding host memory corruption in this case
* sounds like a good idea.
*/
Can we use vhost_vq_get_backend() to check this situation?
IIUC all the vhost devices clear the backend to stop the workers.
This is not racy (if we do after the mutex_lock) and should cover all
cases.
Thanks,
Stefano
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