4.17-stable review patch. If anyone has any objections, please let me know.
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From: Frederic Weisbecker frederic@kernel.org
commit 0a0e0829f990120cef165bbb804237f400953ec2 upstream.
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 anna-maria@linutronix.de Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Anna-Maria Gleixner anna-maria@linutronix.de Cc: stable@vger.kernel.org # 4.14+ Link: https://lkml.kernel.org/r/1533303094-15855-1-git-send-email-frederic@kernel.... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/softirq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -387,7 +387,7 @@ 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