OpenAFS Master Repository branch, master, updated. openafs-devel-1_5_76-4425-gba1cc83

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit ba1cc838ab4a80b7a7787c441a79aca31d84808c
Author: Andrew Deason <adeason@sinenomine.net>
Date:   Tue Oct 28 00:10:56 2014 -0500

    LINUX: Avoid d_revalidate failure on mtpt mismatch
    
    Currently, if afs_linux_dentry_revalidate is given an inode that
    corresponds to a mtpt vcache ('vcp'), it resolves the mtpt to its root
    dir if it's easy to do so (mvid and CMValid are set). Later on, we run
    afs_lookup to see if looking up our dentry's name returns the same
    vcache that we got; afs_lookup presumably will also resolve the mtpt
    if it's easy to do so.
    
    However, it is possible that afs_linux_dentry_revalidate and
    afs_lookup will make different decisions as to whether or not they
    resolve a mtpt to a dir. Specifically, if CMValid is cleared after
    afs_linux_dentry_revalidate checks for it, but before afs_lookup does,
    then afs_lookup will return a different vcache than
    afs_linux_dentry_revalidate is expecting, even though the relevant
    directory entry has not changed. That is, tvc is not equal to vcp, but
    tvc could be a mtpt that resolves to vcp, or vice versa. CMValid can
    be cleared by another thread at virtually any time, since this is
    cleared in some situations when we're not sure if the mtpt resolution
    is still valid (callbacks are broken, vldb cache entries expire, etc).
    
    afs_linux_dentry_revalidate interprets this situation to mean that the
    directory entry has changed, and so it eventually d_drop's the
    associated dentry. The way that this manifests to users is that a
    "fakestatted" mtpt can appear to be deleted effectively randomly, even
    when nothing has changed. This can be a problem because this causes
    the getcwd() syscall to return ENOENT when the working directory
    involves such an affected directory.
    
    To fix this situation, we just detect if afs_lookup returned either
    'vcp' (our possibly-resolved vcache), or the original inode associated
    with the dentry we are revalidating. If the returned vcache matches
    either of these, then the entry is okay and we don't need to
    invalidate or drop anything.
    
    FIXES 131780
    
    Change-Id: Ide1dd224d1ea1e29a82eb7130a010877cf4e9fc7
    Reviewed-on: http://gerrit.openafs.org/11559
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
    Tested-by: Anders Kaseorg <andersk@mit.edu>
    Reviewed-by: Anders Kaseorg <andersk@mit.edu>
    Reviewed-by: D Brashear <shadow@your-file-system.com>

 src/afs/LINUX/osi_vnodeops.c |   29 ++++++++++++++++++++++++++++-
 1 files changed, 28 insertions(+), 1 deletions(-)

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