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...
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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