[PATCH] sched: sched_rt_periodic_timer vs cpu hotplug

[Peter Zijlstra <peterz@infradead.org>]

Subject: sched: sched_rt_periodic_timer vs cpu hotplug
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Mon Nov 16 10:28:09 CET 2009

Heiko reported a case where a timer interrupt managed to reference a
root_domain structure that was already freed by a concurrent
hot-un-plug operation.

Solve this like the regular sched_domain stuff is also synchronized,
by adding a synchronize_sched() stmt to the free path, this ensures
that a root_domain stays present for any atomic section that could
have observed it.

Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> 
---
 kernel/sched.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -7921,6 +7921,8 @@ sd_parent_degenerate(struct sched_domain
 
 static void free_rootdomain(struct root_domain *rd)
 {
+	synchronize_sched();
+
 	cpupri_cleanup(&rd->cpupri);
 
 	free_cpumask_var(rd->rto_mask);