linux-kernel - [tip:smp/hotplug] cpu/hotplug: Use stop_machine_cpuslocked() in takedown

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Message-ID: <tip-210e21331fc3a396af640cec652be769d146e49f@git.kernel.org>
Date:   Fri, 26 May 2017 01:40:35 -0700
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        hpa@...or.com, rostedt@...dmis.org, bigeasy@...utronix.de,
        paulmck@...ux.vnet.ibm.com, peterz@...radead.org
Subject: [tip:smp/hotplug] cpu/hotplug: Use stop_machine_cpuslocked() in
 takedown_cpu()

Commit-ID:  210e21331fc3a396af640cec652be769d146e49f
Gitweb:     http://git.kernel.org/tip/210e21331fc3a396af640cec652be769d146e49f
Author:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Wed, 24 May 2017 10:15:28 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 26 May 2017 10:10:42 +0200

cpu/hotplug: Use stop_machine_cpuslocked() in takedown_cpu()

takedown_cpu() is a cpu hotplug function invoking stop_machine(). The cpu
hotplug machinery holds the hotplug lock for write.

stop_machine() invokes get_online_cpus() as well. This is correct, but
prevents the conversion of the hotplug locking to a percpu rwsem.

Use stop_machine_cpuslocked() to avoid the nested call.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Link: http://lkml.kernel.org/r/20170524081548.423292433@linutronix.de

---
 kernel/cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index e4389ac..142d889 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -701,7 +701,7 @@ static int takedown_cpu(unsigned int cpu)
 	/*
 	 * So now all preempt/rcu users must observe !cpu_active().
 	 */
-	err = stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
+	err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
 	if (err) {
 		/* CPU refused to die */
 		irq_unlock_sparse();