[tip:sched/core] stop_machine: Fix^2 race between stop_two_cpus() and stop_cpus()

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  177c53d943368fc97644ebc0a250dc8e2d124250
Gitweb:     http://git.kernel.org/tip/177c53d943368fc97644ebc0a250dc8e2d124250
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 28 Feb 2014 13:39:05 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 11 Mar 2014 11:33:47 +0100

stop_machine: Fix^2 race between stop_two_cpus() and stop_cpus()

We must use smp_call_function_single(.wait=1) for the
irq_cpu_stop_queue_work() to ensure the queueing is actually done under
stop_cpus_lock. Without this we could have dropped the lock by the time
we do the queueing and get the race we tried to fix.

Fixes: 7053ea1a34fa ("stop_machine: Fix race between stop_two_cpus() and stop_cpus()")

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140228123905.GK3104@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/stop_machine.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 84571e0..01fbae5 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -293,7 +293,7 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
 	 */
 	smp_call_function_single(min(cpu1, cpu2),
 				 &irq_cpu_stop_queue_work,
-				 &call_args, 0);
+				 &call_args, 1);
 	lg_local_unlock(&stop_cpus_lock);
 	preempt_enable();