From e5ab012c3271990e8457055c25cafddc1ae8aa6b Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 20 Feb 2013 16:15:36 +0100 Subject: [PATCH] nohz: Make tick_nohz_irq_exit() irq safe As it stands, irq_exit() may or may not be called with irqs disabled, depending on __ARCH_IRQ_EXIT_IRQS_DISABLED that the arch can define. It makes tick_nohz_irq_exit() unsafe. For example two interrupts can race in tick_nohz_stop_sched_tick(): the inner most one computes the expiring time on top of the timer list, then it's interrupted right before reprogramming the clock. The new interrupt enqueues a new timer list timer, it reprogram the clock to take it into account and it exits. The CPUs resumes the inner most interrupt and performs the clock reprogramming without considering the new timer list timer. This regression has been introduced by: 280f06774afedf849f0b34248ed6aff57d0f6908 ("nohz: Separate out irq exit and idle loop dyntick logic") Let's fix it right now with the appropriate protections. A saner long term solution will be to remove __ARCH_IRQ_EXIT_IRQS_DISABLED and mandate that irq_exit() is called with interrupts disabled. Signed-off-by: Frederic Weisbecker Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Linus Torvalds Cc: #v3.2+ Link: http://lkml.kernel.org/r/1361373336-11337-1-git-send-email-fweisbec@gmail.com Signed-off-by: Thomas Gleixner --- kernel/time/tick-sched.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 314b9ee07edf..520592ab6aa4 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -565,14 +565,19 @@ void tick_nohz_idle_enter(void) */ void tick_nohz_irq_exit(void) { + unsigned long flags; struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); if (!ts->inidle) return; - /* Cancel the timer because CPU already waken up from the C-states*/ + local_irq_save(flags); + + /* Cancel the timer because CPU already waken up from the C-states */ menu_hrtimer_cancel(); __tick_nohz_idle_enter(ts); + + local_irq_restore(flags); } /**