[RFC PATCH 4/6] stop_machine: kill stop_cpus_mutex

[Oleg Nesterov <oleg@redhat.com>]

Change the users of stop_cpus_mutex to rely on stop_work_alloc() and
stop_work_free(). This means that 2 stop_cpus() can run in parallel
as long a their cpumask's do not overlap.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/stop_machine.c |   16 ++++++----------
 1 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 3d5d810..4b23875 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -343,9 +343,6 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
 	cpu_stop_queue_work(cpu, work_buf);
 }
 
-/* static data for stop_cpus */
-static DEFINE_MUTEX(stop_cpus_mutex);
-
 static void queue_stop_cpus_work(const struct cpumask *cpumask,
 				 cpu_stop_fn_t fn, void *arg,
 				 struct cpu_stop_done *done)
@@ -412,10 +409,9 @@ int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 {
 	int ret;
 
-	/* static works are used, process one request at a time */
-	mutex_lock(&stop_cpus_mutex);
+	stop_work_alloc(cpumask, true);
 	ret = __stop_cpus(cpumask, fn, arg);
-	mutex_unlock(&stop_cpus_mutex);
+	stop_work_free(cpumask);
 	return ret;
 }
 
@@ -442,10 +438,10 @@ int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 	int ret;
 
 	/* static works are used, process one request at a time */
-	if (!mutex_trylock(&stop_cpus_mutex))
+	if (!stop_work_alloc(cpumask, false))
 		return -EAGAIN;
 	ret = __stop_cpus(cpumask, fn, arg);
-	mutex_unlock(&stop_cpus_mutex);
+	stop_work_free(cpumask);
 	return ret;
 }
 
@@ -643,7 +639,7 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
 	msdata.num_threads = num_active_cpus() + 1;	/* +1 for local */
 
 	/* No proper task established and can't sleep - busy wait for lock. */
-	while (!mutex_trylock(&stop_cpus_mutex))
+	while (!stop_work_alloc(cpus, false))
 		cpu_relax();
 
 	/* Schedule work on other CPUs and execute directly for local CPU */
@@ -656,8 +652,8 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
 	/* Busy wait for completion. */
 	while (!completion_done(&done.completion))
 		cpu_relax();
+	stop_work_free(cpus);
 
-	mutex_unlock(&stop_cpus_mutex);
 	return ret ?: done.ret;
 }
 
-- 
1.5.5.1