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dm cache: prevent corruption caused by discard_block_size > cache_block_size

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If the discard block size is larger than the cache block size we will
not properly quiesce IO to a region that is about to be discarded.  This
results in a race between a cache migration where no copy is needed, and
a write to an adjacent cache block that's within the same large discard
block.

Workaround this by limiting the discard_block_size to cache_block_size.
Also limit the max_discard_sectors to cache_block_size.

A more comprehensive fix that introduces range locking support in the
bio_prison and proper quiescing of a discard range that spans multiple
cache blocks is already in development.

Reported-by: Morgan Mears <Morgan.Mears@netapp.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Acked-by: Heinz Mauelshagen <heinzm@redhat.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Mike Snitzer 2014-03-20 10:11:15 -04:00
parent 428e469864
commit d132cc6d9e
1 changed files with 3 additions and 34 deletions
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37
drivers/md/dm-cache-target.c
View file

@ -239,7 +239,7 @@ struct cache {
*/
dm_dblock_t discard_nr_blocks;
unsigned long *discard_bitset;
uint32_t discard_block_size; /* a power of 2 times sectors per block */
uint32_t discard_block_size;
/*
* Rather than reconstructing the table line for the status we just
@ -2171,35 +2171,6 @@ static int create_cache_policy(struct cache *cache, struct cache_args *ca,
return 0;
}
/*
* We want the discard block size to be a power of two, at least the size
* of the cache block size, and have no more than 2^14 discard blocks
* across the origin.
*/
#define MAX_DISCARD_BLOCKS (1 << 14)
static bool too_many_discard_blocks(sector_t discard_block_size,
sector_t origin_size)
{
(void) sector_div(origin_size, discard_block_size);
return origin_size > MAX_DISCARD_BLOCKS;
}
static sector_t calculate_discard_block_size(sector_t cache_block_size,
sector_t origin_size)
{
sector_t discard_block_size;
discard_block_size = roundup_pow_of_two(cache_block_size);
if (origin_size)
while (too_many_discard_blocks(discard_block_size, origin_size))
discard_block_size *= 2;
return discard_block_size;
}
#define DEFAULT_MIGRATION_THRESHOLD 2048
static int cache_create(struct cache_args *ca, struct cache **result)
@ -2321,9 +2292,7 @@ static int cache_create(struct cache_args *ca, struct cache **result)
}
clear_bitset(cache->dirty_bitset, from_cblock(cache->cache_size));
cache->discard_block_size =
calculate_discard_block_size(cache->sectors_per_block,
cache->origin_sectors);
cache->discard_block_size = cache->sectors_per_block;
cache->discard_nr_blocks = oblock_to_dblock(cache, cache->origin_blocks);
cache->discard_bitset = alloc_bitset(from_dblock(cache->discard_nr_blocks));
if (!cache->discard_bitset) {
@ -3120,7 +3089,7 @@ static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
/*
* FIXME: these limits may be incompatible with the cache device
*/
limits->max_discard_sectors = cache->discard_block_size * 1024;
limits->max_discard_sectors = cache->discard_block_size;
limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
}