OpenAFS Master Repository branch, openafs-stable-1_6_x, updated. openafs-stable-1_6_22_1-12-gef5fe95

[Gerrit Code Review]

The following commit has been merged in the openafs-stable-1_6_x branch:
commit ef5fe95fdf4e063daafcfee4435f0f9026bf9ada
Author: Mark Vitale <mvitale@sinenomine.net>
Date:   Thu Nov 30 20:26:46 2017 -0500

    LINUX: Avoid d_invalidate() during afs_ShakeLooseVCaches()
    
    With recent changes to d_invalidate's semantics (it returns void in Linux 3.11,
    and always returns success in RHEL 7.4), it has become increasingly clear that
    d_invalidate() is not the best function for use in our best-effort
    (nondisruptive) attempt to free up vcaches that is afs_ShakeLooseVCaches().
    The new d_invalidate() semantics always force the invalidation of a directory
    dentry, which contradicts our desire to be nondisruptive, especially when
    that directory is being used as the current working directory for a process.
    Our call to d_invalidate(), intended to merely probe for whether a dentry
    can be discarded without affecting other consumers, instead would cause
    processes using that dentry as a CWD to receive ENOENT errors from getcwd().
    
    A previous commit (c3bbf0b4444db88192eea4580ac9e9ca3de0d286) tried to address
    this issue by calling d_prune_aliases() instead of d_invalidate(), but
    d_prune_aliases() does not recursively descend into children of the given
    dentry while pruning, leaving it an incomplete solution for our use-case.
    
    To address these issues, modify the shakeloose routine TryEvictDentries() to
    call shrink_dcache_parent() and maybe __d_drop() for directories, and
    d_prune_aliases() for non-directories, instead of d_invalidate().  (Calls to
    d_prune_aliases() for directories have already been removed by reverting commit
    c3bbf0b4444db88192eea4580ac9e9ca3de0d286.)
    
    Just like d_invalidate(), shrink_dcache_parent() has been around "forever"
    (since pre-git v2.6.12).  Also like d_invalidate(), it "walks" the parent
    dentry's subdirectories and "shrinks" (unhashes) unused dentries.  But unlike
    d_invalidate(), shrink_dcache_parent() will not unhash an in-use dentry, and
    has never changed its signature or semantics.
    
    d_prune_aliases() has also been available "forever", and has also never changed
    its signature or semantics.  The lack of recursive descent is not an issue for
    non-directories, which cannot have such children.
    
    [kaduk@mit.edu: apply review feedback to fix locking and avoid extraneous
    changes, and reword commit message]
    
    Reviewed-on: https://gerrit.openafs.org/12830
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    (cherry picked from commit afbc199f152cc06edc877333f229604c28638d07)
    
    Reviewed-on: https://gerrit.openafs.org/12851
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Tested-by: Benjamin Kaduk <kaduk@mit.edu>
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
    (cherry picked from commit 4feec06c7bdc7102ae654cff20eb02650ec32800)
    
    Change-Id: Id509e51f027bd96df155e7ed714e0c7dfce126eb
    Reviewed-on: https://gerrit.openafs.org/12860
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Andrew Deason <adeason@dson.org>
    Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>

 src/afs/LINUX/osi_vcache.c |   51 +++++++++++++++++++++++++++++++++++++------
 1 files changed, 44 insertions(+), 7 deletions(-)

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