OpenAFS Master Repository branch, openafs-stable-1_6_x, updated. openafs-stable-1_6_17-20-gc77ca20

[Gerrit Code Review]

The following commit has been merged in the openafs-stable-1_6_x branch:
commit c77ca20f3eb72d69930259214d782918c561b8ba
Author: Mark Vitale <mvitale@sinenomine.net>
Date:   Thu Mar 27 06:36:59 2014 -0400

    DAFS: large volume support - fileserver crash after "addled bitmap"
    
    Any DAFS fileserver operation that allocates a new vnode but fails
    to update the vnode index will crash:
    
    "Fatal Rx error: assertion failed: --vp->nWaiters >= 0,
    				file: ../vol/volume.c, line: nnnn"
    
    Note: This crash was exposed by other bugs (to be addressed in future
    commits) in OpenAFS large volume support.  However, there may
    be other failure paths (unrelated to large volumes) that expose
    this error as well.
    
    When VAllocVnode() must allocate a new vnode but fails while
    updating the vnode index file (e.g. an "addled bitmap" due to other
    bugs in working with a vnode index larger than 2^31 bytes), it branches
    to common recovery logic at label error_encountered:.
    
    Part of this recovery is to call VFreeBitmapEntry_r().  Commit
    08ffe3e81d875b58ae5fe4c5733845d5132913a0 added a VOL_FREE_BITMAP_WAIT
    flag to VFreeBitmapEntry() in order to prevent races with VAllocBitmapEntry().
    If the caller specifies VOL_FREE_BITMAP_WAIT, VFreeBitmapEntry_r will
    call VCreateReservation_r() and VWaitExclusiveState_r().  However, the
    exit from VFreeBitmapEntry_r() calls VCancelReservation_r() unconditionally.
    This works correctly with the majority of callers to VFreeBitmapEntry_r,
    which do specify the VOL_FREE_BITMAP_WAIT flag.
    
    However, the VAllocVnode() error_encountered logic must specify 0 for
    this flag because the thread is already in an exclusive state
    (VOL_STATE_VNODE_ALLOC).  This correctly causes VFreeBitmapEntry_r() to
    forgo both the reservation and wait-for-exclusive-state.  However, before
    exit it erroneously calls VCancelReservation_r().  We now have unbalanced
    reservations (nWaiters); this causes an assert when the VAllocVnode()
    error_encountered recovery code later calls VCancelReservation_r()
    for what it believes is its own prior reservation.
    
    Modify VFreeBitmapEntry_r() to make its final VCancelReservation_r()
    conditional on flag VOL_FREE_BITMAP_WAIT.
    
    Reviewed-on: http://gerrit.openafs.org/11983
    Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
    Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
    Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    (cherry picked from commit d833ba768064a32a19c6b0b94ffb0d8a3a40a089)
    
    Change-Id: Ia146ca55b1c0497d475357e61eaeb061a11bd597
    Reviewed-on: https://gerrit.openafs.org/12209
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
    Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>

 src/vol/volume.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

-- 
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