Commit 5ec2481b authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

hrtimers: Move SMP function call to thread context 



smp_call_function_* must not be called from softirq context.

But clock_was_set() which calls on_each_cpu() is called from softirq
context to implement a delayed clock_was_set() for the timer interrupt
handler. Though that almost never gets invoked. A recent change in the
resume code uses the softirq based delayed clock_was_set to support
Xens resume mechanism.

linux-next contains a new warning which warns if smp_call_function_*
is called from softirq context which gets triggered by that Xen
change.

Fix this by moving the delayed clock_was_set() call to a work context.

Reported-and-tested-by: default avatarArtem Savkov <artem.savkov@gmail.com>
Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Konrad Wilk <konrad.wilk@oracle.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: xen-devel@lists.xen.org
Cc: stable@vger.kernel.org
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 332962f2

kernel/hrtimer.c

+15 −22
Original line number Diff line number Diff line
@@ -721,17 +721,20 @@ static int hrtimer_switch_to_hres(void) 
	return 1;

}



static void clock_was_set_work(struct work_struct *work)

{

	clock_was_set();

}



static DECLARE_WORK(hrtimer_work, clock_was_set_work);



/*

 * Called from timekeeping code to reprogramm the hrtimer interrupt

 * device. If called from the timer interrupt context we defer it to

 * softirq context.

 * Called from timekeeping and resume code to reprogramm the hrtimer

 * interrupt device on all cpus.

 */

void clock_was_set_delayed(void)

{

	struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);



	cpu_base->clock_was_set = 1;

	__raise_softirq_irqoff(HRTIMER_SOFTIRQ);

	schedule_work(&hrtimer_work);

}



#else
@@ -775,12 +778,7 @@ void clock_was_set(void) 
 * During resume we might have to reprogram the high resolution timer

 * interrupt on all online CPUs.  However, all other CPUs will be

 * stopped with IRQs interrupts disabled so the clock_was_set() call

 * must be deferred to the softirq.

 *

 * The one-shot timer has already been programmed to fire immediately

 * (see tick_resume_oneshot()) and this interrupt will trigger the

 * softirq to run early enough to correctly reprogram the timers on

 * all CPUs.

 * must be deferred.

 */

void hrtimers_resume(void)

{
@@ -789,8 +787,10 @@ void hrtimers_resume(void) 
	WARN_ONCE(!irqs_disabled(),

		  KERN_INFO "hrtimers_resume() called with IRQs enabled!");



	cpu_base->clock_was_set = 1;

	__raise_softirq_irqoff(HRTIMER_SOFTIRQ);

	/* Retrigger on the local CPU */

	retrigger_next_event(NULL);

	/* And schedule a retrigger for all others */

	clock_was_set_delayed();

}



static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)
@@ -1441,13 +1441,6 @@ void hrtimer_peek_ahead_timers(void) 


static void run_hrtimer_softirq(struct softirq_action *h)

{

	struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);



	if (cpu_base->clock_was_set) {

		cpu_base->clock_was_set = 0;

		clock_was_set();

	}



	hrtimer_peek_ahead_timers();

}

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