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dm cache: fix race affecting dirty block count

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nr_dirty is updated without locking, causing it to drift so that it is
non-zero (either a small positive integer, or a very large one when an
underflow occurs) even when there are no actual dirty blocks.  This was
due to a race between the workqueue and map function accessing nr_dirty
in parallel without proper protection.

People were seeing under runs due to a race on increment/decrement of
nr_dirty, see: https://lkml.org/lkml/2014/6/3/648

Fix this by using an atomic_t for nr_dirty.

Reported-by: roma1390@gmail.com
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Anssi Hannula 2014-08-01 11:55:47 -04:00 committed by Mike Snitzer
parent d8c712ea47
commit 44fa816bb7
1 changed files with 6 additions and 7 deletions
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13
drivers/md/dm-cache-target.c
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@ -231,7 +231,7 @@ struct cache {
/*
* cache_size entries, dirty if set
*/
dm_cblock_t nr_dirty;
atomic_t nr_dirty;
unsigned long *dirty_bitset;
/*
@ -492,7 +492,7 @@ static bool is_dirty(struct cache *cache, dm_cblock_t b)
static void set_dirty(struct cache *cache, dm_oblock_t oblock, dm_cblock_t cblock)
{
if (!test_and_set_bit(from_cblock(cblock), cache->dirty_bitset)) {
cache->nr_dirty = to_cblock(from_cblock(cache->nr_dirty) + 1);
atomic_inc(&cache->nr_dirty);
policy_set_dirty(cache->policy, oblock);
}
}
@ -501,8 +501,7 @@ static void clear_dirty(struct cache *cache, dm_oblock_t oblock, dm_cblock_t cbl
{
if (test_and_clear_bit(from_cblock(cblock), cache->dirty_bitset)) {
policy_clear_dirty(cache->policy, oblock);
cache->nr_dirty = to_cblock(from_cblock(cache->nr_dirty) - 1);
if (!from_cblock(cache->nr_dirty))
if (atomic_dec_return(&cache->nr_dirty) == 0)
dm_table_event(cache->ti->table);
}
}
@ -2269,7 +2268,7 @@ static int cache_create(struct cache_args *ca, struct cache **result)
atomic_set(&cache->quiescing_ack, 0);
r = -ENOMEM;
cache->nr_dirty = 0;
atomic_set(&cache->nr_dirty, 0);
cache->dirty_bitset = alloc_bitset(from_cblock(cache->cache_size));
if (!cache->dirty_bitset) {
*error = "could not allocate dirty bitset";
@ -2808,7 +2807,7 @@ static void cache_status(struct dm_target *ti, status_type_t type,
residency = policy_residency(cache->policy);
DMEMIT("%u %llu/%llu %u %llu/%llu %u %u %u %u %u %u %llu ",
DMEMIT("%u %llu/%llu %u %llu/%llu %u %u %u %u %u %u %lu ",
(unsigned)(DM_CACHE_METADATA_BLOCK_SIZE >> SECTOR_SHIFT),
(unsigned long long)(nr_blocks_metadata - nr_free_blocks_metadata),
(unsigned long long)nr_blocks_metadata,
@ -2821,7 +2820,7 @@ static void cache_status(struct dm_target *ti, status_type_t type,
(unsigned) atomic_read(&cache->stats.write_miss),
(unsigned) atomic_read(&cache->stats.demotion),
(unsigned) atomic_read(&cache->stats.promotion),
(unsigned long long) from_cblock(cache->nr_dirty));
(unsigned long) atomic_read(&cache->nr_dirty));
if (writethrough_mode(&cache->features))
DMEMIT("1 writethrough ");