linux-kernel - Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send

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Date:	Wed, 15 May 2013 11:45:28 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123
 native_smp_send_reschedule

On Thu, May 09, 2013 at 02:58:59PM +0200, Borislav Petkov wrote:
> On Thu, May 09, 2013 at 02:50:40PM +0200, Borislav Petkov wrote:
> > Looks like we're sending a resched IPI to a cpu which is not online
> > yet in order to start the MCE polling timer. So the rcu* options are
> > kinda unlikely to be related, AFAICT.
> 
> On a second thought, they must be somehow indirectly related because I
> had "rcu_nocbs=4-7" on the command line and have the warning on the same
> CPUs: 4 - 7.
> 
> Actually, NO_HZ_FULL_ALL makes all CPUs full dynticks so I'd guess the
> RCU callback offloading happens on all of them, thus the warning can
> happen on every CPU which is in full dynticks mode but not online yet.

Does the following patch help?

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 63098a5..68b1f26 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2371,7 +2371,7 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
 static void rcu_kick_nohz_cpu(int cpu)
 {
 #ifdef CONFIG_NO_HZ_FULL
-	if (tick_nohz_full_cpu(cpu))
+	if (tick_nohz_full_cpu(cpu) && cpu_online(cpu))
 		smp_send_reschedule(cpu);
 #endif /* #ifdef CONFIG_NO_HZ_FULL */
 }

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