dm cache: share cache-metadata object across inactive and active DM tables
If a DM table is reloaded with an inactive table when the device is not suspended (normal procedure for LVM2), then there will be two dm-bufio objects that can diverge. This can lead to a situation where the inactive table uses bufio to read metadata at the same time the active table writes metadata -- resulting in the inactive table having stale metadata buffers once it is promoted to the active table slot. Fix this by using reference counting and a global list of cache metadata objects to ensure there is only one metadata object per metadata device. Signed-off-by: NJoe Thornber <ejt@redhat.com> Signed-off-by: NMike Snitzer <snitzer@redhat.com> Cc: stable@vger.kernel.org
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