From: Oleg Nesterov 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 Acked-by: Steven Rostedt Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- kernel/hrtimer.c | 11 ++++++----- kernel/timer.c | 11 ++++++----- 2 files changed, 12 insertions(+), 10 deletions(-) diff -puN kernel/hrtimer.c~migrate_timers-add-comment-use-spinlock_irq kernel/hrtimer.c --- a/kernel/hrtimer.c~migrate_timers-add-comment-use-spinlock_irq +++ a/kernel/hrtimer.c @@ -1612,9 +1612,11 @@ 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++) { @@ -1623,8 +1625,7 @@ 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 */ diff -puN kernel/timer.c~migrate_timers-add-comment-use-spinlock_irq kernel/timer.c --- a/kernel/timer.c~migrate_timers-add-comment-use-spinlock_irq +++ a/kernel/timer.c @@ -1435,9 +1435,11 @@ static void __cpuinit migrate_timers(int 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 } 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 */ _