Commit 35de589c authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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powerpc/time: improve decrementer clockevent processing 



The stop/shutdown op should not use decrementer_set_next_event because
that sets decrementers_next_tb to now + decrementer_max, which means a
decrementer interrupt that occurs after that time will call the
clockevent event handler unexpectedly. Set next_tb to ~0 here to prevent
any clock event call. Init all clockevents to stopped.

Then the decrementer clockevent device always has event_handler set and
applicable because we know the clock event device was not stopped. So
make this call unconditional to show that it is always called. next_tb
need not be set to ~0 before the event handler is called because it will
stop the clockevent device if there is no other timer.

Finally, the timer broadcast interrupt should not modify next_tb because
it is not involved with the local decrementer clockevent on this CPU.

This doesn't fix a known bug, just tidies the code.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220124143930.3923442-3-npiggin@gmail.com
parent cf74ff52

arch/powerpc/kernel/time.c

+10 −8
Original line number Diff line number Diff line
@@ -107,7 +107,12 @@ struct clock_event_device decrementer_clockevent = { 
};

EXPORT_SYMBOL(decrementer_clockevent);



DEFINE_PER_CPU(u64, decrementers_next_tb);

/*

 * This always puts next_tb beyond now, so the clock event will never fire

 * with the usual comparison, no need for a separate test for stopped.

 */

#define DEC_CLOCKEVENT_STOPPED ~0ULL

DEFINE_PER_CPU(u64, decrementers_next_tb) = DEC_CLOCKEVENT_STOPPED;

EXPORT_SYMBOL_GPL(decrementers_next_tb);

static DEFINE_PER_CPU(struct clock_event_device, decrementers);
@@ -645,8 +650,6 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt) 


	now = get_tb();

	if (now >= *next_tb) {

		*next_tb = ~(u64)0;

		if (evt->event_handler)

		evt->event_handler(evt);

		__this_cpu_inc(irq_stat.timer_irqs_event);

	} else {
@@ -666,9 +669,6 @@ EXPORT_SYMBOL(timer_interrupt); 
#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST

void timer_broadcast_interrupt(void)

{

	u64 *next_tb = this_cpu_ptr(&decrementers_next_tb);



	*next_tb = ~(u64)0;

	tick_receive_broadcast();

	__this_cpu_inc(irq_stat.broadcast_irqs_event);

}
@@ -894,7 +894,9 @@ static int decrementer_set_next_event(unsigned long evt, 


static int decrementer_shutdown(struct clock_event_device *dev)

{

	decrementer_set_next_event(decrementer_max, dev);

	__this_cpu_write(decrementers_next_tb, DEC_CLOCKEVENT_STOPPED);

	set_dec_or_work(decrementer_max);



	return 0;

}