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  • Jonathan Brassow's avatar
    DM-RAID: Fix RAID10's check for sufficient redundancy · 55ebbb59
    Jonathan Brassow authored
    Before attempting to activate a RAID array, it is checked for sufficient
    redundancy.  That is, we make sure that there are not too many failed
    devices - or devices specified for rebuild - to undermine our ability to
    activate the array.  The current code performs this check twice - once to
    ensure there were not too many devices specified for rebuild by the user
    ('validate_rebuild_devices') and again after possibly experiencing a failure
    to read the superblock ('analyse_superblocks').  Neither of these checks are
    sufficient.  The first check is done properly but with insufficient
    information about the possible failure state of the devices to make a good
    determination if the array can be activated.  The second check is simply
    done wrong in the case of RAID10 because it doesn't account for the
    independence of the stripes (i.e. mirror sets).  The solution is to use the
    properly written check ('validate_rebuild_devices'), but perform the check
    after the superblocks have been read and we know which devices have failed.
    This gives us one check instead of two and performs it in a location where
    it can be done right.
    Only RAID10 was affected and it was affected in the following ways:
    - the code did not properly catch the condition where a user specified
      a device for rebuild that already had a failed device in the same mirror
      set.  (This condition would, however, be caught at a deeper level in MD.)
    - the code triggers a false positive and denies activation when devices in
      independent mirror sets have failed - counting the failures as though they
      were all in the same set.
    The most likely place this error was introduced (or this patch should have
    been included) is in commit 4ec1e369
     - first introduced in v3.7-rc1.
    Consequently this fix should also go in v3.7.y, however there is a
    small conflict on the .version in raid_target, so I'll submit a
    separate patch to -stable.
    Signed-off-by: default avatarJonathan Brassow <>
    Signed-off-by: default avatarNeilBrown <>