OpenAFS Master Repository branch, master, updated. openafs-devel-1_5_76-4524-gb22c586

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit b22c586bcdf785c489009ab96cbb572181cb9b09
Author: Marc Dionne <marc.dionne@your-file-system.com>
Date:   Fri Dec 19 10:11:53 2014 -0500

    Unix CM: Avoid using stale DV in afs_StoreAllSegments
    
    It was reported in RT 131976 that on Linux some file
    corruption was observed when doing mmap writes to
    a file substantially larger than the cache size.
    
    osi_VM_StoreAllSegments drops locks and asks the OS to flush
    any dirty pages in the file 's mapping.  This will trigger
    calls into our writepage op, and if the number of dirty
    cache chunks is too high (as will happen for a file larger
    than the cache size), afs_DoPartialWrite will recursively
    call afs_StoreAllSegments and some chunks will be written
    back to the server.  After potentially doing this several
    times, control will return to the original afs_StoreAllSegments.
    
    At that point the data version that was stored before
    osi_VM_StoreAllSegments is no longer correct, leading to
    possible data corruption.
    
    Triggering this bug requires writing a file larger than the
    cache so that partial stores are done, and writing enough
    data to exceed the system's maximum dirty ratio and cause
    it to initiate writeback.
    
    To fix, just wait until after osi_VM_StoreAllSegments to
    look at and store the data version.
    
    FIXES 131976
    
    Change-Id: I959f06b5a7a51171e7ed70189620e9d11d52efa2
    Reviewed-on: http://gerrit.openafs.org/11644
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>

 src/afs/afs_segments.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

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