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Date: Fri, 30 Sep 2011 10:00:06 -0700
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Steven Rostedt <rostedt@goodmis.org>
CC: Tejun Heo <tj@kernel.org>, Rusty Russell <rusty@rustcorp.com.au>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC] stop_machine: make stop_machine safe and efficient
 to call early
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On 09/30/2011 09:34 AM, Steven Rostedt wrote:
> Doesn't interrupts need to be disabled here too? As stop machine
> functions also guarantee that they will not be interrupted by
> interrupts. -- Steve

Good point.

    J

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@citrix.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index ba5070c..a45b36d 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -485,6 +485,17 @@ 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) {
+		unsigned long flags;
+		int ret;
+
+		local_save_flags(flags);
+		ret = (*fn)(data);
+		local_irq_restore(flags);
+
+		return ret;
+	}
+
 	/* 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);