[tip:sched/core] stop_machine: Change __stop_cpus() to rely on cpu_stop_queue_work()

[tip-bot for Oleg Nesterov <tipbot@zytor.com>]

Commit-ID:  4aff1ca6970afbf9cd916c34a9c442c8ccba905e
Gitweb:     http://git.kernel.org/tip/4aff1ca6970afbf9cd916c34a9c442c8ccba905e
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sun, 15 Nov 2015 20:33:23 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 23 Nov 2015 09:48:19 +0100

stop_machine: Change __stop_cpus() to rely on cpu_stop_queue_work()

Change queue_stop_cpus_work() to return true if it queues at least one
work, this means that the caller should wait.

__stop_cpus() can check the value returned by queue_stop_cpus_work() and
avoid done.executed, just like stop_one_cpu() does.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Milos Vyletel <milos@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20151115193323.GA8262@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/stop_machine.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 68b73c4..ed2019a 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -318,12 +318,13 @@ bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
 /* static data for stop_cpus */
 static DEFINE_MUTEX(stop_cpus_mutex);
 
-static void queue_stop_cpus_work(const struct cpumask *cpumask,
+static bool queue_stop_cpus_work(const struct cpumask *cpumask,
 				 cpu_stop_fn_t fn, void *arg,
 				 struct cpu_stop_done *done)
 {
 	struct cpu_stop_work *work;
 	unsigned int cpu;
+	bool queued = false;
 
 	/*
 	 * Disable preemption while queueing to avoid getting
@@ -336,9 +337,12 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
 		work->fn = fn;
 		work->arg = arg;
 		work->done = done;
-		cpu_stop_queue_work(cpu, work);
+		if (cpu_stop_queue_work(cpu, work))
+			queued = true;
 	}
 	lg_global_unlock(&stop_cpus_lock);
+
+	return queued;
 }
 
 static int __stop_cpus(const struct cpumask *cpumask,
@@ -347,9 +351,11 @@ 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);
+	if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
+		return -ENOENT;
 	wait_for_completion(&done.completion);
-	return done.executed ? done.ret : -ENOENT;
+	WARN_ON(!done.executed);
+	return done.ret;
 }
 
 /**