From: Mike Snitzer <snitzer@xxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit d132cc6d9e92424bb9d4fd35f5bd0e55d583f4be upstream.
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@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Acked-by: Joe Thornber <ejt@xxxxxxxxxx>
Acked-by: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
drivers/md/dm-cache-target.c | 37 +++----------------------------------
1 file changed, 3 insertions(+), 34 deletions(-)
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 6ab68e058a0a..d64bf7d6c8fe 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -162,7 +162,7 @@ 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
@@ -1908,35 +1908,6 @@ 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)
@@ -2041,9 +2012,7 @@ 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) {
@@ -2630,7 +2599,7 @@ 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;
}
--
1.9.3
--
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