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Commit d82f0b0f authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

migrate_timers: add comment, use spinlock_irq() 



Add the comment to explain why the double lock in migrate_timers()
can't deadlock.

Change the code to use spinlock_irq() instead of local_irq_disable()
+ spin_lock().

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 6a55617e

kernel/hrtimer.c

+6 −5
Original line number Diff line number Diff line
@@ -1620,9 +1620,11 @@ static void migrate_hrtimers(int cpu) 
	new_base = &get_cpu_var(hrtimer_bases);



	tick_cancel_sched_timer(cpu);



	local_irq_disable();

	spin_lock(&new_base->lock);

	/*

	 * The caller is globally serialized and nobody else

	 * takes two locks at once, deadlock is not possible.

	 */

	spin_lock_irq(&new_base->lock);

	spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);



	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
@@ -1631,8 +1633,7 @@ static void migrate_hrtimers(int cpu) 
	}



	spin_unlock(&old_base->lock);

	spin_unlock(&new_base->lock);

	local_irq_enable();

	spin_unlock_irq(&new_base->lock);

	put_cpu_var(hrtimer_bases);

}

#endif /* CONFIG_HOTPLUG_CPU */

kernel/timer.c

+6 −5
Original line number Diff line number Diff line
@@ -1435,9 +1435,11 @@ static void __cpuinit migrate_timers(int cpu) 
	BUG_ON(cpu_online(cpu));

	old_base = per_cpu(tvec_bases, cpu);

	new_base = get_cpu_var(tvec_bases);



	local_irq_disable();

	spin_lock(&new_base->lock);

	/*

	 * The caller is globally serialized and nobody else

	 * takes two locks at once, deadlock is not possible.

	 */

	spin_lock_irq(&new_base->lock);

	spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);



	BUG_ON(old_base->running_timer);
@@ -1452,8 +1454,7 @@ static void __cpuinit migrate_timers(int cpu) 
	}



	spin_unlock(&old_base->lock);

	spin_unlock(&new_base->lock);

	local_irq_enable();

	spin_unlock_irq(&new_base->lock);

	put_cpu_var(tvec_bases);

}

#endif /* CONFIG_HOTPLUG_CPU */