From 19fa1a6756ed9e92daa9537c03b47d6b55cc2316 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Tue, 17 Dec 2013 12:09:40 -0500 Subject: 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 Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org --- drivers/md/dm-thin-metadata.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'drivers/md/dm-thin-metadata.c') diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c index 8a30ad54bd46..7da347665552 100644 --- a/drivers/md/dm-thin-metadata.c +++ b/drivers/md/dm-thin-metadata.c @@ -1349,6 +1349,12 @@ dm_thin_id dm_thin_dev_id(struct dm_thin_device *td) return td->id; } +/* + * Check whether @time (of block creation) is older than @td's last snapshot. + * If so then the associated block is shared with the last snapshot device. + * Any block on a device created *after* the device last got snapshotted is + * necessarily not shared. + */ static bool __snapshotted_since(struct dm_thin_device *td, uint32_t time) { return td->snapshotted_time > time; @@ -1458,6 +1464,20 @@ int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block) return r; } +int dm_pool_block_is_used(struct dm_pool_metadata *pmd, dm_block_t b, bool *result) +{ + int r; + uint32_t ref_count; + + down_read(&pmd->root_lock); + r = dm_sm_get_count(pmd->data_sm, b, &ref_count); + if (!r) + *result = (ref_count != 0); + up_read(&pmd->root_lock); + + return r; +} + bool dm_thin_changed_this_transaction(struct dm_thin_device *td) { int r; -- cgit v1.2.3