linux-kernel - [PATCH 2/8] stop_machine: don't disable preemption in stop_two

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Date:	Sun, 15 Nov 2015 20:33:14 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Milos Vyletel <milos@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/8] stop_machine: don't disable preemption in
	stop_two_cpus()

Now that stop_two_cpus() path does not check cpu_active() we can remove
preempt_disable(), it was only needed to ensure that stop_machine() can
not be called after we observe cpu_active() == T and before we queue the
new work.

Also, turn the pointless and confusing ->executed check into WARN_ON().
We know that both works must be executed, otherwise we have a bug. And
in fact I think that done->executed should die, see the next changes.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/stop_machine.c |   11 +++--------
 1 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 1a66a95..17f01a9 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -258,7 +258,6 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
 	struct cpu_stop_work work1, work2;
 	struct multi_stop_data msdata;
 
-	preempt_disable();
 	msdata = (struct multi_stop_data){
 		.fn = fn,
 		.data = arg,
@@ -277,16 +276,12 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
 
 	if (cpu1 > cpu2)
 		swap(cpu1, cpu2);
-	if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2)) {
-		preempt_enable();
+	if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
 		return -ENOENT;
-	}
-
-	preempt_enable();
 
 	wait_for_completion(&done.completion);
-
-	return done.executed ? done.ret : -ENOENT;
+	WARN_ON(!done.executed);
+	return done.ret;
 }
 
 /**
-- 
1.5.5.1

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