linux-kernel - [RFC][PATCH 02/13] stop_machine: Fix stop_cpus_in

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Date:   Fri, 26 Jul 2019 16:54:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, juri.lelli@...hat.com
Cc:     linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        luca.abeni@...tannapisa.it, bristot@...hat.com,
        balsini@...roid.com, dvyukov@...gle.com, tglx@...utronix.de,
        vpillai@...italocean.com, rostedt@...dmis.org,
        Valentin Schneider <valentin.schneider@....com>,
        Aaron Lu <aaron.lwe@...il.com>, keescook@...omium.org,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Phil Auld <pauld@...hat.com>, torvalds@...ux-foundation.org,
        Tim Chen <tim.c.chen@...ux.intel.com>, fweisbec@...il.com,
        subhra.mazumdar@...cle.com,
        Julien Desfossez <jdesfossez@...italocean.com>, pjt@...gle.com,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>, kerrnel@...gle.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [RFC][PATCH 02/13] stop_machine: Fix stop_cpus_in_progress ordering

Make sure the entire for loop has stop_cpus_in_progress set.

Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Aaron Lu <aaron.lwe@...il.com>
Cc: keescook@...omium.org
Cc: mingo@...nel.org
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Phil Auld <pauld@...hat.com>
Cc: torvalds@...ux-foundation.org
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: fweisbec@...il.com
Cc: subhra.mazumdar@...cle.com
Cc: tglx@...utronix.de
Cc: Julien Desfossez <jdesfossez@...italocean.com>
Cc: pjt@...gle.com
Cc: Nishanth Aravamudan <naravamudan@...italocean.com>
Cc: Aubrey Li <aubrey.intel@...il.com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: kerrnel@...gle.com
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/0fd8fd4b99b9b9aa88d8b2dff897f7fd0d88f72c.1559129225.git.vpillai@digitalocean.com
---
 kernel/stop_machine.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -383,6 +383,7 @@ static bool queue_stop_cpus_work(const s
 	 */
 	preempt_disable();
 	stop_cpus_in_progress = true;
+	barrier();
 	for_each_cpu(cpu, cpumask) {
 		work = &per_cpu(cpu_stopper.stop_work, cpu);
 		work->fn = fn;
@@ -391,6 +392,7 @@ static bool queue_stop_cpus_work(const s
 		if (cpu_stop_queue_work(cpu, work))
 			queued = true;
 	}
+	barrier();
 	stop_cpus_in_progress = false;
 	preempt_enable();