From 0a8a2e78b7eece7c65884fcff9f98dc0fce89ee4 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 24 Jan 2012 18:59:44 +0100 Subject: [PATCH] timer: Fix bad idle check on irq entry idle_cpu() is called on irq entry to guess if we need to call tick_check_idle(). This way we can catch up with jiffies if the tick was stopped, stop accounting idle time during the interrupt and maintain the sched clock if it is unstable. But if we are going to exit the idle loop to schedule a new task (ie: if we have a task in the runqueue or a remotely enqueued ttwu to perform), the idle_cpu() check will return 0 such that we miss the call to tick_check_idle() for all interrupts happening before we schedule the new task. As a result these interrupts and the softirqs coming along may deal with stale jiffies values, bad sched clock values, and won't substract their time from the idle time accounting. Fix this with using is_idle_task() instead that strictly checks that we are running the idle task, without caring about the fact we are going to schedule a task soon. Signed-off-by: Frederic Weisbecker Cc: Peter Zijlstra Cc: John Stultz Cc: Ingo Molnar Link: http://lkml.kernel.org/r/1327427984-23282-3-git-send-email-fweisbec@gmail.com Signed-off-by: Thomas Gleixner --- kernel/softirq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 4eb3a0fa351e..5ace266bc0e6 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -297,7 +297,7 @@ void irq_enter(void) int cpu = smp_processor_id(); rcu_irq_enter(); - if (idle_cpu(cpu) && !in_interrupt()) { + if (is_idle_task(current) && !in_interrupt()) { /* * Prevent raise_softirq from needlessly waking up ksoftirqd * here, as softirq will be serviced on return from interrupt.