This is a note to let you know that I've just added the patch titled
dm cache: fix race affecting dirty block count
to the 3.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-cache-fix-race-affecting-dirty-block-count.patch
and it can be found in the queue-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 44fa816bb778edbab6b6ddaaf24908dd6295937e Mon Sep 17 00:00:00 2001
From: Anssi Hannula <anssi.hannula@xxxxxx>
Date: Fri, 1 Aug 2014 11:55:47 -0400
Subject: dm cache: fix race affecting dirty block count
From: Anssi Hannula <anssi.hannula@xxxxxx>
commit 44fa816bb778edbab6b6ddaaf24908dd6295937e upstream.
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@xxxxxxxxx
Signed-off-by: Anssi Hannula <anssi.hannula@xxxxxx>
Signed-off-by: Joe Thornber <ejt@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm-cache-target.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -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
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 *ca
{
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_arg
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_targe
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_targe
(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 ");
Patches currently in stable-queue which might be from anssi.hannula@xxxxxx are
queue-3.15/dm-cache-fix-race-affecting-dirty-block-count.patch
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