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migrate_timers: add comment, use spinlock_irq()

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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: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Oleg Nesterov 2008-08-20 16:46:04 -07:00 committed by Ingo Molnar
parent 6a55617ed5
commit d82f0b0f6f
2 changed files with 12 additions and 10 deletions
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11
kernel/hrtimer.c
View File

@ -1620,9 +1620,11 @@ static void migrate_hrtimers(int cpu)
new_base = &get_cpu_var(hrtimer_bases); new_base = &get_cpu_var(hrtimer_bases);
tick_cancel_sched_timer(cpu); tick_cancel_sched_timer(cpu);
/*
local_irq_disable(); * The caller is globally serialized and nobody else
spin_lock(&new_base->lock); * takes two locks at once, deadlock is not possible.
*/
spin_lock_irq(&new_base->lock);
spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING); spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) { 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(&old_base->lock);
spin_unlock(&new_base->lock); spin_unlock_irq(&new_base->lock);
local_irq_enable();
put_cpu_var(hrtimer_bases); put_cpu_var(hrtimer_bases);
} }
#endif /* CONFIG_HOTPLUG_CPU */ #endif /* CONFIG_HOTPLUG_CPU */

11
kernel/timer.c
View File

@ -1435,9 +1435,11 @@ static void __cpuinit migrate_timers(int cpu)
BUG_ON(cpu_online(cpu)); BUG_ON(cpu_online(cpu));
old_base = per_cpu(tvec_bases, cpu); old_base = per_cpu(tvec_bases, cpu);
new_base = get_cpu_var(tvec_bases); new_base = get_cpu_var(tvec_bases);
/*
local_irq_disable(); * The caller is globally serialized and nobody else
spin_lock(&new_base->lock); * takes two locks at once, deadlock is not possible.
*/
spin_lock_irq(&new_base->lock);
spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING); spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
BUG_ON(old_base->running_timer); BUG_ON(old_base->running_timer);
@ -1452,8 +1454,7 @@ static void __cpuinit migrate_timers(int cpu)
} }
spin_unlock(&old_base->lock); spin_unlock(&old_base->lock);
spin_unlock(&new_base->lock); spin_unlock_irq(&new_base->lock);
local_irq_enable();
put_cpu_var(tvec_bases); put_cpu_var(tvec_bases);
} }
#endif /* CONFIG_HOTPLUG_CPU */ #endif /* CONFIG_HOTPLUG_CPU */