linux-kernel - Re: [PATCH 1/2] virtio_balloon: fix race by fill and leak

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Date:	Fri, 1 Jan 2016 10:26:32 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Rafael Aquini <aquini@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] virtio_balloon: fix race by fill and leak

On Mon, Dec 28, 2015 at 08:35:12AM +0900, Minchan Kim wrote:
> During my compaction-related stuff, I encountered a bug
> with ballooning.
> 
> With repeated inflating and deflating cycle, guest memory(
> ie, cat /proc/meminfo | grep MemTotal) is decreased and
> couldn't be recovered.
> 
> The reason is balloon_lock doesn't cover release_pages_balloon
> so struct virtio_balloon fields could be overwritten by race
> of fill_balloon(e,g, vb->*pfns could be critical).
> 
> This patch fixes it in my test.
> 
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

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

> ---
>  drivers/virtio/virtio_balloon.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 7efc32945810..7d3e5d0e9aa4 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -209,8 +209,8 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
>  	 */
>  	if (vb->num_pfns != 0)
>  		tell_host(vb, vb->deflate_vq);
> -	mutex_unlock(&vb->balloon_lock);
>  	release_pages_balloon(vb);
> +	mutex_unlock(&vb->balloon_lock);
>  	return num_freed_pages;
>  }
>  
> -- 
> 1.9.1
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