From 80d20d35af1edd632a5e7a3b9c0ab7ceff92769e Mon Sep 17 00:00:00 2001 From: Anna-Maria Gleixner Date: Tue, 31 Jul 2018 18:13:58 +0200 Subject: [PATCH 1/2] nohz: Fix local_timer_softirq_pending() local_timer_softirq_pending() checks whether the timer softirq is pending with: local_softirq_pending() & TIMER_SOFTIRQ. This is wrong because TIMER_SOFTIRQ is the softirq number and not a bitmask. So the test checks for the wrong bit. Use BIT(TIMER_SOFTIRQ) instead. Fixes: 5d62c183f9e9 ("nohz: Prevent a timer interrupt storm in tick_nohz_stop_sched_tick()") Signed-off-by: Anna-Maria Gleixner Signed-off-by: Thomas Gleixner Reviewed-by: Paul E. McKenney Reviewed-by: Daniel Bristot de Oliveira Acked-by: Frederic Weisbecker Cc: bigeasy@linutronix.de Cc: peterz@infradead.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180731161358.29472-1-anna-maria@linutronix.de --- kernel/time/tick-sched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index da9455a6b42b..5b33e2f5c0ed 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -642,7 +642,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) static inline bool local_timer_softirq_pending(void) { - return local_softirq_pending() & TIMER_SOFTIRQ; + return local_softirq_pending() & BIT(TIMER_SOFTIRQ); } static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) From 0a0e0829f990120cef165bbb804237f400953ec2 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 3 Aug 2018 15:31:34 +0200 Subject: [PATCH 2/2] nohz: Fix missing tick reprogram when interrupting an inline softirq The full nohz tick is reprogrammed in irq_exit() only if the exit is not in a nesting interrupt. This stands as an optimization: whether a hardirq or a softirq is interrupted, the tick is going to be reprogrammed when necessary at the end of the inner interrupt, with even potential new updates on the timer queue. When soft interrupts are interrupted, it's assumed that they are executing on the tail of an interrupt return. In that case tick_nohz_irq_exit() is called after softirq processing to take care of the tick reprogramming. But the assumption is wrong: softirqs can be processed inline as well, ie: outside of an interrupt, like in a call to local_bh_enable() or from ksoftirqd. Inline softirqs don't reprogram the tick once they are done, as opposed to interrupt tail softirq processing. So if a tick interrupts an inline softirq processing, the next timer will neither be reprogrammed from the interrupting tick's irq_exit() nor after the interrupted softirq processing. This situation may leave the tick unprogrammed while timers are armed. To fix this, simply keep reprogramming the tick even if a softirq has been interrupted. That can be optimized further, but for now correctness is more important. Note that new timers enqueued in nohz_full mode after a softirq gets interrupted will still be handled just fine through self-IPIs triggered by the timer code. Reported-by: Anna-Maria Gleixner Signed-off-by: Frederic Weisbecker Signed-off-by: Thomas Gleixner Tested-by: Anna-Maria Gleixner Cc: stable@vger.kernel.org # 4.14+ Link: https://lkml.kernel.org/r/1533303094-15855-1-git-send-email-frederic@kernel.org --- kernel/softirq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 75ffc1d1a2e0..6f584861d329 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -390,7 +390,7 @@ static inline void tick_irq_exit(void) /* Make sure that timer wheel updates are propagated */ if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) { - if (!in_interrupt()) + if (!in_irq()) tick_nohz_irq_exit(); } #endif