[tip:sched/urgent] sched: Sched_rt_periodic_timer vs cpu hotplug

[tip-bot for Peter Zijlstra <a.p.zijlstra@chello.nl>]

Commit-ID:  047106adcc85e3023da210143a6ab8a55df9e0fc
Gitweb:     http://git.kernel.org/tip/047106adcc85e3023da210143a6ab8a55df9e0fc
Author:     Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Mon, 16 Nov 2009 10:28:09 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 16 Nov 2009 10:46:27 +0100

sched: Sched_rt_periodic_timer vs cpu hotplug

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>
Cc: Gregory Haskins <ghaskins@novell.com>
Cc: Siddha Suresh B <suresh.b.siddha@intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
LKML-Reference: <1258363873.26714.83.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index cea2bea..3c91f11 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7912,6 +7912,8 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 
 static void free_rootdomain(struct root_domain *rd)
 {
+	synchronize_sched();
+
 	cpupri_cleanup(&rd->cpupri);
 
 	free_cpumask_var(rd->rto_mask);