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Commit 189c3fd6 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge
Browse files

stop_machine: make stop_machine safe and efficient to call early 



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

[ Fixes from AKPM:
   - add comment
   - local_irq_flags, not save_flags
   - also call hard_irq_disable() for systems which need it

  Tejun suggested using an explicit flag rather than just looking at
  the online cpu count. ]

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
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>
parent d5d9a3b1

kernel/stop_machine.c

+22 −0
Original line number Original line Diff line number Diff line
@@ -41,6 +41,7 @@ struct cpu_stopper { 
};

};





static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);

static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);

static bool stop_machine_initialized = false;





static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)

static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)

{

{
@@ -386,6 +387,8 @@ static int __init cpu_stop_init(void) 
	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);

	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);

	register_cpu_notifier(&cpu_stop_cpu_notifier);

	register_cpu_notifier(&cpu_stop_cpu_notifier);





	stop_machine_initialized = true;



	return 0;

	return 0;

}

}

early_initcall(cpu_stop_init);

early_initcall(cpu_stop_init);
@@ -485,6 +488,25 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) 
					    .num_threads = num_online_cpus(),

					    .num_threads = num_online_cpus(),

					    .active_cpus = cpus };

					    .active_cpus = cpus };





	if (!stop_machine_initialized) {

		/*

		 * Handle the case where stop_machine() is called

		 * early in boot before stop_machine() has been

		 * initialized.

		 */

 		unsigned long flags;

		int ret;



		WARN_ON_ONCE(smdata.num_threads != 1);



		local_irq_save(flags);

		hard_irq_disable();

		ret = (*fn)(data);

		local_irq_restore(flags);



		return ret;

	}



	/* Set the initial state and stop all online cpus. */

	/* Set the initial state and stop all online cpus. */

	set_state(&smdata, STOPMACHINE_PREPARE);

	set_state(&smdata, STOPMACHINE_PREPARE);

	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);

	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);