OpenAFS Master Repository branch, master, updated. BP-openafs-stable-1_8_x-241-g930d8ee

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit 930d8ee638112ca8bf27a9528c0a527cfab54c7d
Author: Mark Vitale <mvitale@sinenomine.net>
Date:   Fri Aug 17 18:48:08 2018 -0400

    volser: ensure GCTrans transaction walk remains valid
    
    Commit bc56f5cc97a982ee29219e6f258b372dbfe1a020 ("volser: Delete
    timed-out temporary volumes") introduced new logic to GCTrans().
    Unfortunately, part of this logic temporarily drops VTRANS_LOCK in order
    to call VPurgeVolume().  While this lock is dropped, other volser_trans
    may be added or deleted from the allTrans list.  Therefore, GCTrans
    should not trust the next pointer (nt = tt->next) which was obtained
    before the lock was dropped.
    
    One symptom observed in the field was a segfault while examining
    tt->volume.  Neither tt nor volume were valid any longer, since tt had
    been set from a stale nt at the top of the loop.
    
    To repair, improve, and clarify this logic:
    - Refactor so nt is assigned correctly and as late as possible.
    - Add comments to explain the placement of the assigns to future
    maintainers.
    
    Change-Id: Ibd3a504bddd3622730aa349576341e20f2f27836
    Reviewed-on: https://gerrit.openafs.org/13286
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
    Tested-by: BuildBot <buildbot@rampaginggeek.com>

 src/volser/voltrans.c |   20 +++++++++++++++++---
 1 files changed, 17 insertions(+), 3 deletions(-)

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