linux-kernel - Re: [PATCH] xen-blkback: fix memory leak when persistent grants are used

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Message-ID: <52E242CE.4040400@citrix.com>
Date:	Fri, 24 Jan 2014 11:39:10 +0100
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	Matt Wilson <msw@...ux.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Matt Rushton <mrushton@...zon.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xen.org>,
	Anthony Liguori <aliguori@...zon.com>,
	Matt Wilson <msw@...zon.com>
Subject: Re: [PATCH] xen-blkback: fix memory leak when persistent grants are
 used

On 23/01/14 20:28, Matt Wilson wrote:
> From: Matt Rushton <mrushton@...zon.com>
> 
> Currently shrink_free_pagepool() is called before the pages used for
> persistent grants are released via free_persistent_gnts(). This
> results in a memory leak when a VBD that uses persistent grants is
> torn down.

Good catch.

> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: "Roger Pau Monné" <roger.pau@...rix.com>
> Cc: Ian Campbell <Ian.Campbell@...rix.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: xen-devel@...ts.xen.org
> Cc: Anthony Liguori <aliguori@...zon.com>
> Signed-off-by: Matt Rushton <mrushton@...zon.com>
> Signed-off-by: Matt Wilson <msw@...zon.com>
> ---
>  drivers/block/xen-blkback/blkback.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index 6620b73..30ef7b3 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -625,9 +625,6 @@ purge_gnt_list:
>  			print_stats(blkif);
>  	}
>  
> -	/* Since we are shutting down remove all pages from the buffer */
> -	shrink_free_pagepool(blkif, 0 /* All */);
> -
>  	/* Free all persistent grant pages */
>  	if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
>  		free_persistent_gnts(blkif, &blkif->persistent_gnts,
> @@ -636,6 +633,9 @@ purge_gnt_list:
>  	BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
>  	blkif->persistent_gnt_c = 0;

I think we should also add:

flush_work(&blkif->persistent_purge_work);

Here in case there's some pending purge work going on, which could also
add pages to the free list after we have cleaned it.

> +	/* Since we are shutting down remove all pages from the buffer */
> +	shrink_free_pagepool(blkif, 0 /* All */);
> +
>  	if (log_stats)
>  		print_stats(blkif);
>  
> 

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