From c925077c33fc9a546e7cf6c3be2adf4a2afe2608 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 6 Nov 2013 17:18:30 +0100 Subject: [PATCH] posix-timers: Fix full dynticks CPUs kick on timer rescheduling A posix CPU timer can be rearmed while it is firing or after it is notified with a signal. This can happen for example with timers that were set with a non zero interval in timer_settime(). This rearming can happen in two places: 1) On timer firing time, which happens on the target's tick. If the timer can't trigger a signal because it is ignored, it reschedules itself to honour the timer interval. 2) On signal handling from the timer's notification target. This one can be a different task than the timer's target itself. Once the signal is notified, the notification target rearms the timer, again to honour the timer interval. When a timer is rearmed, we need to notify the full dynticks CPUs such that they restart their tick in case they are running tasks that may have a share in elapsing this timer. Now the 1st case above handles full dynticks CPUs with a call to posix_cpu_timer_kick_nohz() from the posix cpu timer firing code. But the second case ignores the fact that some CPUs may run non-idle tasks with their tick off. As a result, when a timer is resheduled after its signal notification, the full dynticks CPUs may completely ignore it and not tick on the timer as expected This patch fixes this bug by handling both cases in one. All we need is to move the kick to the rearming common code in posix_cpu_timer_schedule(). Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Oleg Nesterov Cc: Steven Rostedt Cc: Olivier Langlois --- kernel/posix-cpu-timers.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 35509c5a3ffb..79747b7d9420 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -1091,7 +1091,8 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) put_task_struct(p); timer->it.cpu.task = p = NULL; timer->it.cpu.expires = 0; - goto out_unlock; + read_unlock(&tasklist_lock); + goto out; } else if (unlikely(p->exit_state) && thread_group_empty(p)) { /* * We've noticed that the thread is dead, but @@ -1100,7 +1101,8 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) */ cpu_timer_sample_group(timer->it_clock, p, &now); clear_dead_task(timer, now); - goto out_unlock; + read_unlock(&tasklist_lock); + goto out; } spin_lock(&p->sighand->siglock); cpu_timer_sample_group(timer->it_clock, p, &now); @@ -1114,10 +1116,11 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) BUG_ON(!irqs_disabled()); arm_timer(timer); spin_unlock(&p->sighand->siglock); - -out_unlock: read_unlock(&tasklist_lock); + /* Kick full dynticks CPUs in case they need to tick on the new timer */ + posix_cpu_timer_kick_nohz(); + out: timer->it_overrun_last = timer->it_overrun; timer->it_overrun = -1; @@ -1257,13 +1260,6 @@ void run_posix_cpu_timers(struct task_struct *tsk) cpu_timer_fire(timer); spin_unlock(&timer->it_lock); } - - /* - * In case some timers were rescheduled after the queue got emptied, - * wake up full dynticks CPUs. - */ - if (tsk->signal->cputimer.running) - posix_cpu_timer_kick_nohz(); } /* -- 2.20.1