On Fri, Jul 20, 2012 at 04:11:00PM +0530, Srivatsa S. Bhat wrote:
> On 07/19/2012 10:45 PM, Paul E. McKenney wrote:
> > On Thu, Jul 19, 2012 at 05:39:30PM +0530, Srivatsa S. Bhat wrote:
> >> Hi Paul,
> >>
> >> While running a CPU hotplug stress test on v3.5-rc7+
> >> (mainline commit 8a7298b7805ab) I hit this warning.
> >> I haven't tried to debug this yet...
> >>
> >> Line number 1550 maps to:
> >>
> >> WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
> >>
> >> inside rcu_do_batch().
> >
> > Hello, Srivatsa,
> >
> > I believe that you need commit a16b7a69 (Prevent __call_rcu() from
> > invoking RCU core on offline CPUs), which is currently in -tip, queued
> > for 3.6. Please see below for the patch.
> >
> > Does this help?
>
> Yes, that fixed it, thanks! :-)
> Sorry for the noise...
May I add your Tested-by?
Thanx, Paul
> Regards,
> Srivatsa S. Bhat
>
> >
> > ------------------------------------------------------------------------
> >
> > rcu: Prevent __call_rcu() from invoking RCU core on offline CPUs
> >
> > The __call_rcu() function will invoke the RCU core, for example, if
> > it detects that the current CPU has too many callbacks. However, this
> > can happen on an offline CPU that is on its way to the idle loop, in
> > which case it is an error to invoke the RCU core, and the excess callbacks
> > will be adopted in any case. This commit therefore adds checks to
> > __call_rcu() for running on an offline CPU, refraining from invoking
> > the RCU core in this case.
> >
> > Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Reviewed-by: Josh Triplett <j...@joshtriplett.org>
> >
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index a4a9c91..ceaa959 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -1904,11 +1904,11 @@ __call_rcu(struct rcu_head *head, void
> > (*func)(struct rcu_head *rcu),
> > * If called from an extended quiescent state, invoke the RCU
> > * core in order to force a re-evaluation of RCU's idleness.
> > */
> > - if (rcu_is_cpu_idle())
> > + if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
> > invoke_rcu_core();
> >
> > - /* If interrupts were disabled, don't dive into RCU core. */
> > - if (irqs_disabled_flags(flags)) {
> > + /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
> > + if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) {
> > local_irq_restore(flags);
> > return;
> > }
> >
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