linux-kernel - [patch] sched: cpu hotplug fix

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Date:	Thu, 12 Feb 2009 11:50:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Thomas Gleixner <tglx@...x.de>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Carsten Emde <ce@...g.ch>, Clark Williams <williams@...hat.com>
Subject: [patch] sched: cpu hotplug fix


The fix below addresses a lockdep warning i triggered with your config.

(You could hit this if you try to use s2ram or hibernation or explicit
CPU hotplug ops.)

	Ingo

-------------->
Subject: sched: cpu hotplug fix
From: Ingo Molnar <mingo@...e.hu>
Date: Thu Feb 12 11:35:40 CET 2009

rq_attach_root() does a kfree() with the runqueue lock held.

That's not a very wise move, fix it.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

Index: tip/kernel/sched.c
===================================================================
--- tip.orig/kernel/sched.c
+++ tip/kernel/sched.c
@@ -7619,20 +7619,26 @@ static void free_rootdomain(struct root_
 
 static void rq_attach_root(struct rq *rq, struct root_domain *rd)
 {
+	struct root_domain *old_rd = NULL;
 	unsigned long flags;
 
 	spin_lock_irqsave(&rq->lock, flags);
 
 	if (rq->rd) {
-		struct root_domain *old_rd = rq->rd;
+		old_rd = rq->rd;
 
 		if (cpumask_test_cpu(rq->cpu, old_rd->online))
 			set_rq_offline(rq);
 
 		cpumask_clear_cpu(rq->cpu, old_rd->span);
 
-		if (atomic_dec_and_test(&old_rd->refcount))
-			free_rootdomain(old_rd);
+		/*
+		 * If we dont want to free the old_rt yet then
+		 * set old_rd to NULL to skip the freeing later
+		 * in this function:
+		 */
+		if (!atomic_dec_and_test(&old_rd->refcount))
+			old_rd = NULL;
 	}
 
 	atomic_inc(&rd->refcount);
@@ -7643,6 +7649,9 @@ static void rq_attach_root(struct rq *rq
 		set_rq_online(rq);
 
 	spin_unlock_irqrestore(&rq->lock, flags);
+
+	if (old_rd)
+		free_rootdomain(old_rd);
 }
 
 static int __init_refok init_rootdomain(struct root_domain *rd, bool bootmem)

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