netdev - Re: [PATCH net 1/2] vhost: use mutex_lock_nested() in vhost_dev_lock

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Message-ID: <20180123175752-mutt-send-email-mst@kernel.org>
Date:   Tue, 23 Jan 2018 17:57:58 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH net 1/2] vhost: use mutex_lock_nested() in
 vhost_dev_lock_vqs()

On Tue, Jan 23, 2018 at 05:27:25PM +0800, Jason Wang wrote:
> We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> hold mutexes of all virtqueues. This may confuse lockdep to report a
> possible deadlock because of trying to hold locks belong to same
> class. Switch to use mutex_lock_nested() to avoid false positive.
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Reported-by: syzbot+dbb7c1161485e61b0241@...kaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 33ac2b1..549771a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -904,7 +904,7 @@ static void vhost_dev_lock_vqs(struct vhost_dev *d)
>  {
>  	int i = 0;
>  	for (i = 0; i < d->nvqs; ++i)
> -		mutex_lock(&d->vqs[i]->mutex);
> +		mutex_lock_nested(&d->vqs[i]->mutex, i);
>  }
>  
>  static void vhost_dev_unlock_vqs(struct vhost_dev *d)
> -- 
> 2.7.4