Subject: Re: [PATCH 1/1] vhost: Provide a kernel warning if mutex is held whilst clean-up in progress

From: Leon Romanovsky <[email-masked]>
Date: Thu, 3 Mar 2022 21:14:36 +0200

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 <[email-masked]>
> Signed-off-by: Lee Jones <[email-masked]>
> ---
>  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

>  		if (dev->vqs[i]->error_ctx)
>  			eventfd_ctx_put(dev->vqs[i]->error_ctx);
> -- 
> 2.35.1.574.g5d30c73bfb-goog
>