From: Yong Zhang <yong.zhang0@gmail.com>
Date: Thu, 28 Jul 2011 11:16:00 +0800
Subject: hotplug: Reread hotplug_pcp on pin_current_cpu() retry
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 1667f95f5a3b114a97cd661ca32c9897f42aea9b
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

When retry happens, it's likely that the task has been migrated to
another cpu (except unplug failed), but it still derefernces the
original hotplug_pcp per cpu data.

Update the pointer to hotplug_pcp in the retry path, so it points to
the current cpu.

Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110728031600.GA338@windriver.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/cpu.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -252,9 +252,11 @@ static DEFINE_PER_CPU(struct hotplug_pcp
  */
 void pin_current_cpu(void)
 {
-	struct hotplug_pcp *hp = this_cpu_ptr(&hotplug_pcp);
+	struct hotplug_pcp *hp;
 
 retry:
+	hp = this_cpu_ptr(&hotplug_pcp);
+
 	if (!hp->unplug || hp->refcount || preempt_count() > 1 ||
 	    hp->unplug == current) {
 		hp->refcount++;