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dm cache: fix race when issuing a POLICY_REPLACE operation

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There is a race between a policy deciding to replace a cache entry,
the core target writing back any dirty data from this block, and other
IO threads doing IO to the same block.

This sort of problem is avoided most of the time by the core target
grabbing a bio prison cell before making the request to the policy.
But for a demotion the core target doesn't know which block will be
demoted, so can't do this in advance.

Fix this demotion race by introducing a callback to the policy interface
that allows the policy to grab the cell on behalf of the core target.

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:
Joe Thornber
2015-05-20 10:30:32 +01:00
committed by Mike Snitzer
parent 54cea3f668
commit fb4100ae7f
5 changed files with 85 additions and 37 deletions
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5
drivers/md/dm-cache-policy-internal.h
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@@ -16,9 +16,10 @@
*/
static inline int policy_map(struct dm_cache_policy *p, dm_oblock_t oblock,
bool can_block, bool can_migrate, bool discarded_oblock,
struct bio *bio, struct policy_result *result)
struct bio *bio, struct policy_locker *locker,
struct policy_result *result)
{
return p->map(p, oblock, can_block, can_migrate, discarded_oblock, bio, result);
return p->map(p, oblock, can_block, can_migrate, discarded_oblock, bio, locker, result);
}
static inline int policy_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)