Re: [PATCH] highres: Do not run the TIMER_SOFTIRQ after switching to highres mode

[Andres Salomon <dilinger@debian.org>]

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Thomas Gleixner wrote:
>>> The question is, how the tick timer gets enqueued in the softirq queue.
>>> Can you isolate the codepath, where this happens ?
> 
> The TIMER_SOFTIRQ runs the hrtimers during bootup until a usable
> clocksource and clock event sources are registered. The switch to high
> resolution mode happens inside of the TIMER_SOFTIRQ, but runs the
> softirq afterwards. That way the tick emulation timer, which was set up
> in the switch to highres might be executed in the softirq context, which
> is a BUG. The rbtree has not to be touched by the softirq after the
> highres switch.
> 

And an additional request, just to make it explicit that we should not
have any NO_SOFTIRQ callbacks in the tree; BUG out if we encounter such
a thing.

Signed-off-by: Andres Salomon <dilinger@debian.org>

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diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 476cb0c..4dcdd09 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1130,6 +1130,7 @@ static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base,
 		if (base->softirq_time.tv64 <= timer->expires.tv64)
 			break;
 
+		BUG_ON(timer->cb_mode == HRTIMER_CB_IRQSAFE_NO_SOFTIRQ);
 		timer_stats_account_hrtimer(timer);
 
 		fn = timer->function;