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

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Date:   Thu, 3 Mar 2022 21:14:36 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     mst@...hat.com, jasowang@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] vhost: Provide a kernel warning if mutex is held
 whilst clean-up in progress

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@...hat.com>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  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
>