Re: [PATCH] RAID5: Change kmem_cache name string of RAID 4/5/6 stripe cache

["H. Peter Anvin" <hpa@zytor.com>]

On 09/19/2013 08:16 PM, Jonathan Brassow wrote:
> The unique portion of the kmem_cache name used when dm-raid is creating
> a RAID 4/5/6 array is the memory address of it's associated 'mddev'
> structure.  This is not always unique.  The memory associated
> with the 'mddev' structure can be freed and a future 'mddev' structure
> can be allocated from the exact same spot.  This causes an identical
> name to the old cache to be created when kmem_cache_create is called.
> If an old name is still present amoung slab_caches due to cache merging,
> the call will fail.  This is not theoretical, I see this regularly when
> performing device-mapper RAID 4/5/6 tests (although, strangely only on
> Fedora-19).
> 
> Making the unique portion of the kmem_cache name based on jiffies fixes
> this problem.
> 
> Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
> ---
>  drivers/md/raid5.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 7ff4f25..f731ce9 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -1618,7 +1618,7 @@ static int grow_stripes(struct r5conf *conf, int num)
>  			"raid%d-%s", conf->level, mdname(conf->mddev));
>  	else
>  		sprintf(conf->cache_name[0],
> -			"raid%d-%p", conf->level, conf->mddev);
> +			"raid%d-%llu", conf->level, get_jiffies_64());
>  	sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);
>  
>  	conf->active_name = 0;
> 

And it is not possible to create two inside the same jiffy?  Seems
unlikely at best.

Why not just use a simple counter?

	-hpa

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