From: Joe Thornber Date: Tue, 17 Dec 2013 17:09:40 +0000 (-0500) Subject: dm thin: fix discard support to a previously shared block X-Git-Tag: v3.14-rc1~130^2~33 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=19fa1a6756ed9e92daa9537c03b47d6b55cc2316;p=pandora-kernel.git 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 --- Reading git-diff-tree failed