[dm-devel] [PATCH] dm bufio: fully initialize shrinker

[Mikulas Patocka]

On Thu, 31 Jul 2014, Greg Thelen wrote:

> 1d3d4437eae1 ("vmscan: per-node deferred work") added a flags field to
> struct shrinker assuming that all shrinkers were zero filled.  The dm
> bufio shrinker is not zero filled, which leaves arbitrary kmalloc() data
> in flags.  So far the only defined flags bit is SHRINKER_NUMA_AWARE.
> But there are proposed patches which add other bits to shrinker.flags
> (e.g. memcg awareness).
> 
> Rather than simply initializing the shrinker, this patch uses kzalloc()
> when allocating the dm_bufio_client to ensure that the embedded shrinker
> and any other similar structures are zeroed.
> 
> This fixes theoretical over aggressive shrinking of dm bufio objects.
> If the uninitialized dm_bufio_client.shrinker.flags contains
> SHRINKER_NUMA_AWARE then shrink_slab() would call the dm shrinker for
> each numa node rather than just once.  This has been broken since 3.12.
> 
> Signed-off-by: Greg Thelen <gthelen at google.com>

Acked-by: Mikulas Patocka <mpatocka at redhat.com>
Cc: stable at vger.kernel.org	#v3.12

> ---
>  drivers/md/dm-bufio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
> index 4e84095833db..d724459860d9 100644
> --- a/drivers/md/dm-bufio.c
> +++ b/drivers/md/dm-bufio.c
> @@ -1541,7 +1541,7 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
>  	BUG_ON(block_size < 1 << SECTOR_SHIFT ||
>  	       (block_size & (block_size - 1)));
>  
> -	c = kmalloc(sizeof(*c), GFP_KERNEL);
> +	c = kzalloc(sizeof(*c), GFP_KERNEL);
>  	if (!c) {
>  		r = -ENOMEM;
>  		goto bad_client;
> -- 
> 2.0.0.526.g5318336
> 
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