1. 12 Aug, 2013 38 commits
  2. 30 Jul, 2013 1 commit
  3. 24 Jul, 2013 1 commit
    • Dave Chinner's avatar
      xfs: di_flushiter considered harmful · e60896d8
      Dave Chinner authored
      When we made all inode updates transactional, we no longer needed
      the log recovery detection for inodes being newer on disk than the
      transaction being replayed - it was redundant as replay of the log
      would always result in the latest version of the inode would be on
      disk. It was redundant, but left in place because it wasn't
      considered to be a problem.
      
      However, with the new "don't read inodes on create" optimisation,
      flushiter has come back to bite us. Essentially, the optimisation
      made always initialises flushiter to zero in the create transaction,
      and so if we then crash and run recovery and the inode already on
      disk has a non-zero flushiter it will skip recovery of that inode.
      As a result, log recovery does the wrong thing and we end up with a
      corrupt filesystem.
      
      Because we have to support old kernel to new kernel upgrades, we
      can't just get rid of the flushiter support in log recovery as we
      might be upgrading from a kernel that doesn't have fully transactional
      inode updates.  Unfortunately, for v4 superblocks there is no way to
      guarantee that log recovery knows about this fact.
      
      We cannot add a new inode format flag to say it's a "special inode
      create" because it won't be understood by older kernels and so
      recovery could do the wrong thing on downgrade. We cannot specially
      detect the combination of zero mode/non-zero flushiter on disk to
      non-zero mode, zero flushiter in the log item during recovery
      because wrapping of the flushiter can result in false detection.
      
      Hence that makes this "don't use flushiter" optimisation limited to
      a disk format that guarantees that we don't need it. And that means
      the only fix here is to limit the "no read IO on create"
      optimisation to version 5 superblocks....
      Reported-by: default avatarMarkus Trippelsdorf <markus@trippelsdorf.de>
      Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
      Reviewed-by: default avatarMark Tinguely <tinguely@sgi.com>
      Signed-off-by: default avatarBen Myers <bpm@sgi.com>
      e60896d8