On Wed, 2012-07-11 at 14:45 +0200, Thomas Gleixner wrote:

On Wed, 11 Jul 2012, Prarit Bhargava wrote:

quoted

On 07/10/2012 06:43 PM, John Stultz wrote:

quoted

clock_was_set() cannot be called from hard interrupt context because
it calls on_each_cpu(). For fixing the widely reported leap seconds
issue it's necessary to call it from the timer interrupt context.

Provide a new function which denotes it in the hrtimer cpu base
structure of the cpu on which it is called and raising the timer
softirq.

We then execute the clock_was_set() notificiation in the timer softirq
context in hrtimer_run_pending().

I wish there was a nicer way to do this ... but looking at the code I can't
figure out a better way.  (no offense John, it's just the way the code is ;) )

Yeah, I had the same discussion with Peter earlier today. There is
only a rather limited set of options.

1) Retrigger the timer interrupt vectors on all CPUs - except the one
   we are running on, but we have no interface for that at the moment

2) Do the nasty __smp_call_function_single() hack

   Preallocate call_single_data for all cpus and do a
   __smp_call_function_single() on all online cpus.

   This can be called from hard interrupt context or irq disabled
   regions.

   That would allow to get rid of the whole delay magic all
   together.

Thoughts?

The __smp_call_function_single() thing isn't particularly pretty either
and a lot more code to boot.. 

static DEFINE_PER_CPU(struct call_single_data, cws_csd);

void clock_was_set(void)
{
	int cpu;

	for_each_online_cpu(cpu) {
		struct call_single_data *csd = &per_cpu(cws_csd, cpu);

		if (csd->flags & CSD_FLAG_LOCK)
			continue; /* a pending request is good enough */

		csd->func = retrigger_next_event;

		__smp_call_function_single(cpu, csd, 0);
	}

	timerfd_clock_was_set();
}

It also is a for_each_cpu loop with preemption disabled, not pretty :/