linux-kernel - [RFC PATCH 13/15] sched: Protect nohz task cpu affinity

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Message-Id: <1292858662-5650-14-git-send-email-fweisbec@gmail.com>
Date:	Mon, 20 Dec 2010 16:24:20 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: [RFC PATCH 13/15] sched: Protect nohz task cpu affinity

Don't allow to change a nohz task cpu affinity as we want them
to be bound to a single CPU and we want this affinity not to
change.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Anton Blanchard <anton@....ibm.com>
Cc: Tim Pepper <lnxninja@...ux.vnet.ibm.com>
---
 kernel/sched.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 4412493..bd0a41f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5712,6 +5712,13 @@ again:
 		goto out;
 	}
 
+	/* Nohz tasks must keep their affinity */
+	if (test_tsk_thread_flag(p, TIF_NOHZ) &&
+	    !cpumask_equal(&p->cpus_allowed, new_mask)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
 	if (p->sched_class->set_cpus_allowed)
 		p->sched_class->set_cpus_allowed(p, new_mask);
 	else {
-- 
1.7.3.2

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