On Wed, Jul 24, 2013 at 03:47:30PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > 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 woul dbe 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 kernl 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 transaction > 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.... > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> Applied. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
