linux-kernel - [tip:sched/core] stop_machine: Don' t disable preemption in stop_two

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Message-ID: <tip-6a19005157c464b47b2082f2617d12bc11198a0d@git.kernel.org>
Date:	Mon, 23 Nov 2015 08:21:48 -0800
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tj@...nel.org, tglx@...utronix.de, efault@....de,
	peterz@...radead.org, prarit@...hat.com, oleg@...hat.com,
	milos@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, mingo@...nel.org, hpa@...or.com
Subject: [tip:sched/core] stop_machine: Don'
 t disable preemption in stop_two_cpus()

Commit-ID:  6a19005157c464b47b2082f2617d12bc11198a0d
Gitweb:     http://git.kernel.org/tip/6a19005157c464b47b2082f2617d12bc11198a0d
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Sun, 15 Nov 2015 20:33:14 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 23 Nov 2015 09:48:18 +0100

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Tejun Heo <tj@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Milos Vyletel <milos@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20151115193314.GA8249@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/stop_machine.c | 11 +++--------
 1 file 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;
 }
 
 /**
--
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