This is a note to let you know that I have just added a patch titled nohz: Make tick_nohz_irq_exit() irq safe to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ >From 2c5afd2674bfea5f6c564dad7d96d0a42251d6ee Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker <fweisbec@xxxxxxxxx> Date: Wed, 20 Feb 2013 16:15:36 +0100 Subject: [PATCH] nohz: Make tick_nohz_irq_exit() irq safe commit e5ab012c3271990e8457055c25cafddc1ae8aa6b upstream. 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 <fweisbec@xxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> #v3.2+ Link: http://lkml.kernel.org/r/1361373336-11337-1-git-send-email-fweisbec@xxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [ luis: backported to 3.5 ] Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx> --- kernel/time/tick-sched.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 4a08472..cc1825f 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -500,12 +500,17 @@ 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; + local_irq_save(flags); + tick_nohz_stop_sched_tick(ts); + + local_irq_restore(flags); } /** -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html