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Commit d132cc6d authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm cache: prevent corruption caused by discard_block_size > cache_block_size 



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: default avatarMorgan Mears <Morgan.Mears@netapp.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Acked-by: default avatarJoe Thornber <ejt@redhat.com>
Acked-by: default avatarHeinz Mauelshagen <heinzm@redhat.com>
Cc: stable@vger.kernel.org
parent 428e4698

drivers/md/dm-cache-target.c

+3 −34
Original line number Diff line number Diff line
@@ -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;

}