From 9b5b2c6660c0c01acf3e2a0e1b878f01380dd88f Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 3 Oct 2012 17:21:53 +0100
Subject: [PATCH 139/414] stomp_machine: Use mutex_trylock when called from
 inactive cpu

If the stop machinery is called from inactive CPU we cannot use
mutex_lock, because some other stomp machine invokation might be in
progress and the mutex can be contended. We cannot schedule from this
context, so trylock and loop.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
---
 kernel/stop_machine.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index bbdef5324410..5f02a3fe729f 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -160,7 +160,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
 
 static void queue_stop_cpus_work(const struct cpumask *cpumask,
 				 cpu_stop_fn_t fn, void *arg,
-				 struct cpu_stop_done *done)
+				 struct cpu_stop_done *done, bool inactive)
 {
 	struct cpu_stop_work *work;
 	unsigned int cpu;
@@ -177,7 +177,12 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
 	 * Make sure that all work is queued on all cpus before we
 	 * any of the cpus can execute it.
 	 */
-	mutex_lock(&stopper_lock);
+	if (!inactive) {
+		mutex_lock(&stopper_lock);
+	} else {
+		while (!mutex_trylock(&stopper_lock))
+			cpu_relax();
+	}
 	for_each_cpu(cpu, cpumask)
 		cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
 	mutex_unlock(&stopper_lock);
@@ -189,7 +194,7 @@ static int __stop_cpus(const struct cpumask *cpumask,
 	struct cpu_stop_done done;
 
 	cpu_stop_init_done(&done, cpumask_weight(cpumask));
-	queue_stop_cpus_work(cpumask, fn, arg, &done);
+	queue_stop_cpus_work(cpumask, fn, arg, &done, false);
 	wait_for_stop_done(&done);
 	return done.executed ? done.ret : -ENOENT;
 }
@@ -564,7 +569,7 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
 	set_state(&smdata, STOPMACHINE_PREPARE);
 	cpu_stop_init_done(&done, num_active_cpus());
 	queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
-			     &done);
+			     &done, true);
 	ret = stop_machine_cpu_stop(&smdata);
 
 	/* Busy wait for completion. */
-- 
2.10.2

