OpenAFS Master Repository branch, master, updated. openafs-devel-1_9_1-501-gd822447

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit d822447c272ed4590f73c4b1c847fc7922950d22
Author: Andrew Deason <adeason@dson.org>
Date:   Sun May 10 17:02:21 2020 -0500

    FBSD: Avoid extra vcache puts in afs_root
    
    Our two 'goto tryagain;' cases in afs_root() have a couple of
    refcounting problems:
    
    - If vget() returns an error, but any of the cases in the first if()
      statement are true (such as, afs_globalVp does not have CStatd set),
      we'll vput() and afs_PutVCache(), but vget() didn't grab a
      reference, since it returned an error. So we'll put references we
      don't actually have.
    
    - If we enter the first if() block when vget() returns a success, we
      vput() the reference we got from vget(), but we also put an
      additional reference by calling afs_PutVCache(). If afs_globalVp
      still points to this same vcache, this can cause afs_globalVp to
      point to a vcache without a ref held for it.
    
    Because of this, if afs_globalVp loses CStatd while we're waiting for
    the vnode lock, this can cause the afs_globalVp vcache to not have any
    refs held for it, which causes all sorts of other possible problems,
    where the usecount for afs_globalVp can drop to 0 when we don't expect
    it to.
    
    To fix these issues, remove the extra afs_PutVCache(), and check for
    an error from vget() before doing the other afs_globalVp-related
    checks.
    
    The relevant code path involved here can be stressed by frequently
    causing lookups via /afs/..., while at the same time causing frequent
    callback breaks on the root vnode. This can be achieved by using an RW
    volume as the root volume (with non-dynroot), and having another
    client constantly modify the root directory in that volume while a
    FreeBSD client constantly does /afs/... lookups in separate pids.
    
    Thanks to tcreech@tcreech.com for reporting and helping investigate
    the relevant issue.
    
    Change-Id: I812d063b3d60ac6eb841863cc7fba3e152393910
    Reviewed-on: https://gerrit.openafs.org/14206
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
    Reviewed-by: Andrew Deason <adeason@sinenomine.net>

 src/afs/FBSD/osi_vfsops.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

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