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authorJoe Thornber <ejt@redhat.com>2013-12-17 12:09:40 -0500
committerMike Snitzer <snitzer@redhat.com>2014-01-07 10:11:43 -0500
commit19fa1a6756ed9e92daa9537c03b47d6b55cc2316 (patch)
tree5e4957a39759e385227995fff9a6e1aa3c99550a /drivers/md/dm-thin.c
parent16961b042db8cc5cf75d782b4255193ad56e1d4f (diff)
downloadlinux-19fa1a6756ed9e92daa9537c03b47d6b55cc2316.tar.bz2
dm thin: fix discard support to a previously shared block
If a snapshot is created and later deleted the origin dm_thin_device's snapshotted_time will have been updated to reflect the snapshot's creation time. The 'shared' flag in the dm_thin_lookup_result struct returned from dm_thin_find_block() is an approximation based on snapshotted_time -- this is done to avoid 0(n), or worse, time complexity. In this case, the shared flag would be true. But because the 'shared' flag reflects an approximation a block can be incorrectly assumed to be shared (e.g. false positive for 'shared' because the snapshot no longer exists). This could result in discards issued to a thin device not being passed down to the pool's underlying data device. To fix this we double check that a thin block is really still in-use after a mapping is removed using dm_pool_block_is_used(). If the reference count for a block is now zero the discard is allowed to be passed down. Also add a 'definitely_not_shared' member to the dm_thin_new_mapping structure -- reflects that the 'shared' flag in the response from dm_thin_find_block() can only be held as definitive if false is returned. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1043527 Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Cc: stable@vger.kernel.org
Diffstat (limited to 'drivers/md/dm-thin.c')
-rw-r--r--drivers/md/dm-thin.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index da65febdb6c4..51e656a3002c 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -512,6 +512,7 @@ struct dm_thin_new_mapping {
unsigned quiesced:1;
unsigned prepared:1;
unsigned pass_discard:1;
+ unsigned definitely_not_shared:1;
struct thin_c *tc;
dm_block_t virt_block;
@@ -683,7 +684,15 @@ static void process_prepared_discard_passdown(struct dm_thin_new_mapping *m)
cell_defer_no_holder(tc, m->cell2);
if (m->pass_discard)
- remap_and_issue(tc, m->bio, m->data_block);
+ if (m->definitely_not_shared)
+ remap_and_issue(tc, m->bio, m->data_block);
+ else {
+ bool used = false;
+ if (dm_pool_block_is_used(tc->pool->pmd, m->data_block, &used) || used)
+ bio_endio(m->bio, 0);
+ else
+ remap_and_issue(tc, m->bio, m->data_block);
+ }
else
bio_endio(m->bio, 0);
@@ -1036,7 +1045,8 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
*/
m = get_next_mapping(pool);
m->tc = tc;
- m->pass_discard = (!lookup_result.shared) && pool->pf.discard_passdown;
+ m->pass_discard = pool->pf.discard_passdown;
+ m->definitely_not_shared = !lookup_result.shared;
m->virt_block = block;
m->data_block = lookup_result.block;
m->cell = cell;