Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH v2] nohz: Fix missing tick reprog while interrupting inline timer softirq | Date | Fri, 3 Aug 2018 15:31:34 +0200 |
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The full nohz tick is reprogrammed on IRQ exit only if we are not in a nesting interrupt. This stands as an optimization: whether we are interrupting a hardirq or a softirq, the tick is going to be reprogrammed eventually in the end of the inner IRQ, with even potential new updates on the timer queue.
Now when we are interrupting softirqs, we always assume that they are executing on IRQ-tail. Indeed 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 IRQ, 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 IRQ-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 us later in userspace with the tick unprogrammed while we can have timers in the queue.
To fix this, simply keep reprogramming the tick if we are in a hardirq interrupting softirq. We can still figure out a way later to restore this optimization while excluding inline softirq processing.
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 <anna-maria@linutronix.de> Tested-by: Anna-Maria Gleixner <anna-maria@linutronix.de> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> --- kernel/softirq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/softirq.c b/kernel/softirq.c index 900dcfe..0980a81 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -386,7 +386,7 @@ 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 -- 2.7.4
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