Messages in this thread | | | Subject | Re: [BUG][next-20170606][bisected 411fe24e6b] WARNING: CPU: 10 PID: 0 at kernel/time/tick-sched.c:791 | From | Abdul Haleem <> | Date | Mon, 12 Jun 2017 12:52:29 +0530 |
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On Fri, 2017-06-09 at 15:09 +0200, Frederic Weisbecker wrote: > On Wed, Jun 07, 2017 at 12:56:53PM +0530, Abdul Haleem wrote: > > Hi, > > > > Test: Trinity (https://github.com/kernelslacker/trinity) > > Machine : Power 8 PowerVM LPAR > > Kernel : 4.12.0-rc4-next-20170606 > > gcc : version 5.2.1 > > config : attached > > > > With commit (411fe24e6b : nohz: Fix collision between tick and other > > hrtimers), a WARNING is seen while running trinity syscall fuzzer > > > > In file kernel/time/tick-sched.c at line 791, a WARN_ON_ONCE is being > > triggered from tick_nohz_stop_sched_tick function. > > > > /* Skip reprogram of event if its not changed */ > > if (ts->tick_stopped && (expires == ts->next_tick)) { > > /* Sanity check: make sure clockevent is actually programmed */ > > if (likely(dev->next_event <= ts->next_tick)) > > goto out; > > > > WARN_ON_ONCE(1); > > printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n", > > basemono, ts->next_tick, dev->next_event, > > hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer)); > > } > > > > Trace logs: > > [22934.302780] ------------[ cut here ]------------ > > [22934.302787] WARNING: CPU: 10 PID: 0 at kernel/time/tick-sched.c:791 > > __tick_nohz_idle_enter+0x2e8/0x570 > > Hi Abdul, > > Thanks for reporting. I've cooked a fix, any chance you could test it?
Hi Frederic,
Thanks for the fix. With given patch on 4.12.0-rc4-next-20170609, test completed with no WARNINGS.
Reported-and-tested-by : Abdul Haleem <abdhalee@linux.vnet.ibm.com>
> -- > From f80041b5209aaf9d02ac25a29a248d0f214ba19f Mon Sep 17 00:00:00 2001 > From: Frederic Weisbecker <fweisbec@gmail.com> > Date: Thu, 8 Jun 2017 16:32:58 +0200 > Subject: [PATCH] nohz: Fix spurious warning when hrtimer and clocksource get > out of sync > > The sanity check ensuring that the tick expiry cache (ts->next_tick) > is actually in sync with the hardware clock (dev->next_event) makes the > wrong assumption that the clock can't be programmed later than the > hrtimer deadline. > > In fact the clock hardware can be programmed later on some conditions > such as: > > * The hrtimer deadline is already in the past. > * The hrtimer deadline is earlier than the minimum delay supported > by the hardware. > > Such conditions can be met when we program the tick, for example if the > last jiffies update hasn't been seen by the current CPU yet, we may > program the hrtimer to a deadline that is earlier than ktime_get() > because last_jiffies_update is our timestamp base to compute the next > tick. > > As a result, we can randomly observe such warning: > > WARNING: CPU: 5 PID: 0 at kernel/time/tick-sched.c:794 tick_nohz_stop_sched_tick kernel/time/tick-sched.c:791 [inline] > Call Trace: > tick_nohz_irq_exit > tick_irq_exit > irq_exit > exiting_irq > smp_call_function_interrupt > smp_call_function_single_interrupt > call_function_single_interrupt > > Therefore, let's rather make sure that the tick expiry cache is sync'ed > with the tick hrtimer deadline, against which it is not supposed to > drift away. The clock hardware instead has its own will and can't be > used as a reliable comparison point. > > Reported-by: Sasha Levin <alexander.levin@verizon.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rik van Riel <riel@redhat.com> > Cc: James Hartsock <hartsjc@redhat.com> > Cc: Tim Wright <tim@binbash.co.uk> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > --- > kernel/time/tick-sched.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 9d31f1e..83c788e 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -768,7 +768,8 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > /* Skip reprogram of event if its not changed */ > if (ts->tick_stopped && (expires == ts->next_tick)) { > /* Sanity check: make sure clockevent is actually programmed */ > - if (likely(dev->next_event <= ts->next_tick)) > + if (tick == KTIME_MAX || > + ts->next_tick == hrtimer_get_expires(&ts->sched_timer)) > goto out; > > WARN_ON_ONCE(1); > @@ -806,8 +807,10 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > goto out; > } > > + hrtimer_set_expires(&ts->sched_timer, tick); > + > if (ts->nohz_mode == NOHZ_MODE_HIGHRES) > - hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED); > + hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); > else > tick_program_event(tick, 1); > out:
-- Regard's
Abdul Haleem IBM Linux Technology Centre
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