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

[Brassow Jonathan <jbrassow@redhat.com>]

I think I can NACK this patch.  It was fixed properly in the kmem code.

 brassow

On Oct 10, 2013, at 5:50 PM, H. Peter Anvin wrote:

> 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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