From: Preeti U Murthy <preeti@linux•vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: paulmck@linux•vnet.ibm.com, paulus@samba•org,
Anton Blanchard <anton@samba•org>,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH] powerpc: irq work racing with timer interrupt can result in timer interrupt hang
Date: Sat, 10 May 2014 21:06:31 +0530 [thread overview]
Message-ID: <536E477F.2070009@linux.vnet.ibm.com> (raw)
In-Reply-To: <1399695993.4481.47.camel@pasglop>
On 05/10/2014 09:56 AM, Benjamin Herrenschmidt wrote:
> On Fri, 2014-05-09 at 15:22 +0530, Preeti U Murthy wrote:
>> in __timer_interrupt() outside the _else_ loop? This will ensure that no
>> matter what, before exiting timer interrupt handler we check for pending
>> irq work.
>
> We still need to make sure that set_next_event() doesn't move the
> dec beyond the next tick if there is a pending timer... maybe we
Sorry, but didn't get this. s/if there is pending timer/if there is
pending irq work ?
> can fix it like this:
We can call set_next_event() from events like hrtimer_cancel() or
hrtimer_forward() as well. In that case we don't come to
decrementer_set_next_event() from __timer_interrupt(). Then, if we race
with irq work, we *do not do* a set_dec(1) ( I am referring to the patch
below ), we might never set the decrementer to fire immediately right?
Or does this scenario never arise?
Regards
Preeti U Murthy
>
> static int decrementer_set_next_event(unsigned long evt,
> struct clock_event_device *dev)
> {
> __get_cpu_var(decrementers_next_tb) = get_tb_or_rtc() + evt;
>
> /* Don't adjust the decrementer if some irq work is pending */
> if (!test_irq_work_pending())
> set_dec(evt);
>
> return 0;
> }
>
> Along with a single occurrence of:
>
> if (test_irq_work_pending())
> set_dec(1);
>
> At the end of __timer_interrupt(), outside if the current else {}
> case, this should work, don't you think ?
>
> What about this completely untested patch ?
>
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index 122a580..ba7e83b 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -503,12 +503,13 @@ void __timer_interrupt(void)
> now = *next_tb - now;
> if (now <= DECREMENTER_MAX)
> set_dec((int)now);
> - /* We may have raced with new irq work */
> - if (test_irq_work_pending())
> - set_dec(1);
> __get_cpu_var(irq_stat).timer_irqs_others++;
> }
>
> + /* We may have raced with new irq work */
> + if (test_irq_work_pending())
> + set_dec(1);
> +
> #ifdef CONFIG_PPC64
> /* collect purr register values often, for accurate calculations */
> if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
> @@ -813,15 +814,11 @@ static void __init clocksource_init(void)
> static int decrementer_set_next_event(unsigned long evt,
> struct clock_event_device *dev)
> {
> - /* Don't adjust the decrementer if some irq work is pending */
> - if (test_irq_work_pending())
> - return 0;
> __get_cpu_var(decrementers_next_tb) = get_tb_or_rtc() + evt;
> - set_dec(evt);
>
> - /* We may have raced with new irq work */
> - if (test_irq_work_pending())
> - set_dec(1);
> + /* Don't adjust the decrementer if some irq work is pending */
> + if (!test_irq_work_pending())
> + set_dec(evt);
>
> return 0;
> }
>
>
>
>
next prev parent reply other threads:[~2014-05-10 15:41 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-09 7:47 [PATCH] powerpc: irq work racing with timer interrupt can result in timer interrupt hang Anton Blanchard
2014-05-09 9:52 ` Preeti U Murthy
2014-05-10 4:26 ` Benjamin Herrenschmidt
2014-05-10 15:36 ` Preeti U Murthy [this message]
2014-05-10 22:25 ` Benjamin Herrenschmidt
2014-05-11 8:15 ` Preeti U Murthy
2014-05-11 8:37 ` Benjamin Herrenschmidt
2014-05-11 8:43 ` Preeti U Murthy
2014-05-11 9:03 ` Benjamin Herrenschmidt
2014-05-11 9:07 ` Preeti U Murthy
2014-05-09 13:41 ` Paul E. McKenney
2014-05-09 21:50 ` Gabriel Paubert
2014-05-09 22:08 ` Paul E. McKenney
2014-05-10 6:33 ` Paul Mackerras
2014-05-10 16:33 ` Paul E. McKenney
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