linux-kernel - [PATCH RFC] stop_machine: make stop_machine safe and efficient to call early

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Message-ID: <4E85EE1F.7050508@goop.org>
Date:	Fri, 30 Sep 2011 09:28:15 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Tejun Heo <tj@...nel.org>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH RFC] stop_machine: make stop_machine safe and efficient to
 call early

Make stop_machine() safe to call early in boot, before SMP has been
set up, by simply calling the callback function directly if there's
only one CPU online.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Cc: Tejun Heo <tj@...nel.org>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: H. Peter Anvin <hpa@...ux.intel.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Steven Rostedt <rostedt@...dmis.org>

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index ba5070c..2df15ca 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -485,6 +485,9 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 					    .num_threads = num_online_cpus(),
 					    .active_cpus = cpus };
 
+	if (smdata.num_threads == 1)
+		return (*fn)(data);
+
 	/* Set the initial state and stop all online cpus. */
 	set_state(&smdata, STOPMACHINE_PREPARE);
 	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);


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