linux-kernel - [PATCH] nohz: don't stop idle tick if softirqs are pending.

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Message-ID: <20080711090922.GA4660@osiris.boeblingen.de.ibm.com>
Date:	Fri, 11 Jul 2008 11:09:22 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Jan Glauber <jan.glauber@...ibm.com>,
	Stefan Weinhuber <wein@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] nohz: don't stop idle tick if softirqs are pending.

Subject: [PATCH] nohz: don't stop idle tick if softirqs are pending.

From: Heiko Carstens <heiko.carstens@...ibm.com>

In case a cpu goes idle but softirqs are pending only an error message is
printed to the console. It may take a very long time until the pending
softirqs will finally be executed. Worst case would be a hanging system.

With this patch the timer tick just continues and the softirqs will be
executed after the next interrupt. Still a delay but better than a
hanging system.

Currently we have at least two device drivers on s390 which under certain
circumstances schedule a tasklet from process context. This is a reason
why we can end up with pending softirqs when going idle. Fixing these
drivers seems to be non-trivial.
However there is no question that the drivers should be fixed.
This patch shouldn't be considered as a bug fix. It just is intended to
keep a system running even if device drivers are buggy.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 kernel/time/tick-sched.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6/kernel/time/tick-sched.c
===================================================================
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -228,6 +228,7 @@ void tick_nohz_stop_sched_tick(void)
 			       local_softirq_pending());
 			ratelimit++;
 		}
+		goto end;
 	}

 	ts->idle_calls++;
--
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