netdev - Re: [PATCH v2 1/1] Add timer to handle OOM situations

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Message-ID: <20160729122035.GE5443@stefanha-x1.localdomain>
Date:	Fri, 29 Jul 2016 13:20:35 +0100
From:	Stefan Hajnoczi <stefanha@...hat.com>
To:	ggarcia@...a.uab.cat
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/1] Add timer to handle OOM situations

On Tue, Jul 26, 2016 at 04:28:21PM +0200, ggarcia@...a.uab.cat wrote:
> @@ -493,6 +524,9 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>  		goto out;
>  	}
>  
> +	setup_timer(&vsock->tx_kick,
> +		    vhost_vsock_rehandle_tx_kick, (unsigned long) NULL);
> +
>  	vqs[VSOCK_VQ_TX] = &vsock->vqs[VSOCK_VQ_TX];
>  	vqs[VSOCK_VQ_RX] = &vsock->vqs[VSOCK_VQ_RX];
>  	vsock->vqs[VSOCK_VQ_TX].handle_kick = vhost_vsock_handle_tx_kick;
> @@ -555,6 +589,7 @@ static int vhost_vsock_dev_release(struct inode *inode, struct file *file)
>  	vhost_dev_stop(&vsock->dev);
>  	vhost_dev_cleanup(&vsock->dev, false);
>  	kfree(vsock->dev.vqs);
> +	del_timer(&vsock->tx_kick);

Please use del_timer_sync() so that we know the timer callback has
finished executing if it's racing with us.

Also please figure out the correct ordering of this call so
vhost_poll_queue() doesn't crash if the timer fires while we are
executing vhost_vsock_dev_release().  In other words, vq and vq->poll
must still be alive when we delete the timer, otherwise the callback
could fire an run on a vq that has already been cleaned up by
vhost_vsock_dev_release().

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