• Mark Fasheh's avatar
    ocfs2: serialize unaligned aio · a11f7e63
    Mark Fasheh authored
    Fix a corruption that can happen when we have (two or more) outstanding
    aio's to an overlapping unaligned region.  Ext4
    (e9e3bcec) and xfs recently had to fix
    similar issues.
    
    In our case what happens is that we can have an outstanding aio on a region
    and if a write comes in with some bytes overlapping the original aio we may
    decide to read that region into a page before continuing (typically because
    of buffered-io fallback).  Since we have no ordering guarantees with the
    aio, we can read stale or bad data into the page and then write it back out.
    
    If the i/o is page and block aligned, then we avoid this issue as there
    won't be any need to read data from disk.
    
    I took the same approach as Eric in the ext4 patch and introduced some
    serialization of unaligned async direct i/o.  I don't expect this to have an
    effect on the most common cases of AIO.  Unaligned aio will be slower
    though, but that's far more acceptable than data corruption.
    Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
    Signed-off-by: default avatarJoel Becker <jlbec@evilplan.org>
    a11f7e63
aops.h 3.83 KB