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author | Joe Thornber <ejt@redhat.com> | 2013-12-17 12:09:40 -0500 |
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committer | Mike Snitzer <snitzer@redhat.com> | 2014-01-07 10:11:43 -0500 |
commit | 19fa1a6756ed9e92daa9537c03b47d6b55cc2316 (patch) | |
tree | 5e4957a39759e385227995fff9a6e1aa3c99550a /drivers/md/dm-thin.c | |
parent | 16961b042db8cc5cf75d782b4255193ad56e1d4f (diff) | |
download | op-kernel-dev-19fa1a6756ed9e92daa9537c03b47d6b55cc2316.zip op-kernel-dev-19fa1a6756ed9e92daa9537c03b47d6b55cc2316.tar.gz |
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.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index da65feb..51e656a 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; |