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    SubjectRe: [BUG] race of RCU vs NOHU
    On Fri, 7 Aug 2009 07:29:57 -0700
    "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

    > On Fri, Aug 07, 2009 at 03:15:29PM +0200, Martin Schwidefsky wrote:
    > > Hi Paul,
    > > I analysed a dump of a hanging 2.6.30 system and found what I think is
    > > a bug of RCU vs NOHZ. There are a number of patches ontop of that
    > > kernel but they should be independent of the bug.
    > >
    > > The systems has 4 cpus and uses classic RCU. cpus #0, #2 and #3 woke up
    > > recently, cpu #1 has been sleeping for 5 minutes, but there is a pending
    > > rcu batch. The timer wheel for cpu #1 is empty, it will continue to
    > > sleep for NEXT_TIMER_MAX_DELTA ticks.
    >
    > Congratulations, Martin! You have exercised what to date has been a
    > theoretical bug identified last year by Manfred Spraul. The fix is to
    > switch from CONFIG_RCU_CLASSIC to CONFIG_RCU_TREE, which was added in
    > 2.6.29.
    >
    > Of course, if you need to work with an old kernel version, you might
    > still need a patch, perhaps for the various -stable versions. If so,
    > please let me know -- otherwise, I will focus forward on CONFIG_RCU_TREE
    > rather than backwards on CONFIG_RCU_CLASSIC.

    SLES11 is 2.6.27 and uses classic RCU. The not-so theoretical bug is
    present there and I think it needs to be fixed :-/

    --
    blue skies,
    Martin.

    "Reality continues to ruin my life." - Calvin.



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