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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: 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
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428e469864
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1 changed files with 3 additions and 34 deletions
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@ -239,7 +239,7 @@ struct cache {
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*/
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*/
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dm_dblock_t discard_nr_blocks;
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dm_dblock_t discard_nr_blocks;
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unsigned long *discard_bitset;
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unsigned long *discard_bitset;
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uint32_t discard_block_size; /* a power of 2 times sectors per block */
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uint32_t discard_block_size;
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/*
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/*
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* Rather than reconstructing the table line for the status we just
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* Rather than reconstructing the table line for the status we just
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@ -2171,35 +2171,6 @@ static int create_cache_policy(struct cache *cache, struct cache_args *ca,
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return 0;
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return 0;
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}
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}
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/*
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* We want the discard block size to be a power of two, at least the size
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* of the cache block size, and have no more than 2^14 discard blocks
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* across the origin.
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*/
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#define MAX_DISCARD_BLOCKS (1 << 14)
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static bool too_many_discard_blocks(sector_t discard_block_size,
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sector_t origin_size)
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{
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(void) sector_div(origin_size, discard_block_size);
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return origin_size > MAX_DISCARD_BLOCKS;
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}
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static sector_t calculate_discard_block_size(sector_t cache_block_size,
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sector_t origin_size)
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{
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sector_t discard_block_size;
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discard_block_size = roundup_pow_of_two(cache_block_size);
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if (origin_size)
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while (too_many_discard_blocks(discard_block_size, origin_size))
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discard_block_size *= 2;
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return discard_block_size;
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}
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#define DEFAULT_MIGRATION_THRESHOLD 2048
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#define DEFAULT_MIGRATION_THRESHOLD 2048
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static int cache_create(struct cache_args *ca, struct cache **result)
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static int cache_create(struct cache_args *ca, struct cache **result)
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@ -2321,9 +2292,7 @@ static int cache_create(struct cache_args *ca, struct cache **result)
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}
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}
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clear_bitset(cache->dirty_bitset, from_cblock(cache->cache_size));
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clear_bitset(cache->dirty_bitset, from_cblock(cache->cache_size));
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cache->discard_block_size =
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cache->discard_block_size = cache->sectors_per_block;
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calculate_discard_block_size(cache->sectors_per_block,
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cache->origin_sectors);
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cache->discard_nr_blocks = oblock_to_dblock(cache, cache->origin_blocks);
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cache->discard_nr_blocks = oblock_to_dblock(cache, cache->origin_blocks);
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cache->discard_bitset = alloc_bitset(from_dblock(cache->discard_nr_blocks));
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cache->discard_bitset = alloc_bitset(from_dblock(cache->discard_nr_blocks));
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if (!cache->discard_bitset) {
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if (!cache->discard_bitset) {
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@ -3120,7 +3089,7 @@ static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
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/*
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/*
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* FIXME: these limits may be incompatible with the cache device
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* FIXME: these limits may be incompatible with the cache device
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*/
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*/
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limits->max_discard_sectors = cache->discard_block_size * 1024;
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limits->max_discard_sectors = cache->discard_block_size;
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limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
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limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
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}
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}
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