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

[tip-bot for Oleg Nesterov]

Commit-ID:  958c5f848e17e216df138cc2161b07b7120e2d15
Gitweb:     http://git.kernel.org/tip/958c5f848e17e216df138cc2161b07b7120e2d15
Author:     Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Sun, 15 Nov 2015 20:33:20 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 23 Nov 2015 09:48:18 +0100

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

Change stop_one_cpu() to return -ENOENT if cpu_stop_queue_work() fails.
Otherwise we know that ->executed must be true after wait_for_completion()
so we can just return done.ret.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Milos Vyletel <milos@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20151115193320.GA8259@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/stop_machine.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 0ec1f16..68b73c4 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -128,9 +128,11 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
 	struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
 
 	cpu_stop_init_done(&done, 1);
-	cpu_stop_queue_work(cpu, &work);
+	if (!cpu_stop_queue_work(cpu, &work))
+		return -ENOENT;
 	wait_for_completion(&done.completion);
-	return done.executed ? done.ret : -ENOENT;
+	WARN_ON(!done.executed);
+	return done.ret;
 }
 
 /* This controls the threads on each CPU. */
--
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