On Wed, Aug 02, 2017 at 05:25:55PM +0100, Jonathan Cameron wrote: > On Tue, 1 Aug 2017 11:46:46 -0700 > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > On Mon, Jul 31, 2017 at 04:27:57PM +0100, Jonathan Cameron wrote: > > > On Mon, 31 Jul 2017 08:04:11 -0700 > > > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > On Mon, Jul 31, 2017 at 12:08:47PM +0100, Jonathan Cameron wrote: > > > > > On Fri, 28 Jul 2017 12:03:50 -0700 > > > > > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > On Fri, Jul 28, 2017 at 06:27:05PM +0100, Jonathan Cameron wrote: > > > > > > > On Fri, 28 Jul 2017 09:55:29 -0700 > > > > > > > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > On Fri, Jul 28, 2017 at 02:24:03PM +0100, Jonathan Cameron wrote: > > > > > > > > > On Fri, 28 Jul 2017 08:44:11 +0100 > > > > > > > > > Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > [ . . . ] > > > > > > > > > > > > > > > > > Ok. Some info. I disabled a few driver (usb and SAS) in the interest of having > > > > > > > > > fewer timer events. Issue became much easier to trigger (on some runs before > > > > > > > > > I could get tracing up and running) > > > > > > > > >e > > > > > > > > > So logs are large enough that pastebin doesn't like them - please shoet if > > > > > > > > >>e another timer period is of interest. > > > > > > > > > > > > > > > > > > https://pastebin.com/iUZDfQGM for the timer trace. > > > > > > > > > https://pastebin.com/3w1F7amH for dmesg. > > > > > > > > > > > > > > > > > > The relevant timeout on the RCU stall detector was 8 seconds. Event is > > > > > > > > > detected around 835. > > > > > > > > > > > > > > > > > > It's a lot of logs, so I haven't identified a smoking gun yet but there > > > > > > > > > may well be one in there. > > > > > > > > > > > > > > > > The dmesg says: > > > > > > > > > > > > > > > > rcu_preempt kthread starved for 2508 jiffies! g112 c111 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 > > > > > > > > > > > > > > > > So I look for "rcu_preempt" timer events and find these: > > > > > > > > > > > > > > > > rcu_preempt-9 [019] .... 827.579114: timer_init: timer=ffff8017d5fc7da0 > > > > > > > > rcu_preempt-9 [019] d..1 827.579115: timer_start: timer=ffff8017d5fc7da0 function=process_timeout > > > > > > > > > > > > > > > > Next look for "ffff8017d5fc7da0" and I don't find anything else. > > > > > > > It does show up off the bottom of what would fit in pastebin... > > > > > > > > > > > > > > rcu_preempt-9 [001] d..1 837.681077: timer_cancel: timer=ffff8017d5fc7da0 > > > > > > > rcu_preempt-9 [001] .... 837.681086: timer_init: timer=ffff8017d5fc7da0 > > > > > > > rcu_preempt-9 [001] d..1 837.681087: timer_start: timer=ffff8017d5fc7da0 function=process_timeout expires=4295101298 [timeout=1] cpu=1 idx=0 flags= > > > > > > > > > > > > Odd. I would expect an expiration... And ten seconds is way longer > > > > > > than the requested one jiffy! > > > > > > > > > > > > > > The timeout was one jiffy, and more than a second later, no expiration. > > > > > > > > Is it possible that this event was lost? I am not seeing any sign of > > > > > > > > this is the trace. > > > > > > > > > > > > > > > > I don't see any sign of CPU hotplug (and I test with lots of that in > > > > > > > > any case). > > > > > > > > > > > > > > > > The last time we saw something like this it was a timer HW/driver problem, > > > > > > > > but it is a bit hard to imagine such a problem affecting both ARM64 > > > > > > > > and SPARC. ;-) > > > > > > > Could be different issues, both of which were hidden by that lockup detector. > > > > > > > > > > > > > > There is an errata work around for the timers on this particular board. > > > > > > > I'm only vaguely aware of it, so may be unconnected. > > > > > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/clocksource/arm_arch_timer.c?h=v4.13-rc2&id=bb42ca47401010fc02901b5e8f79e40a26f208cb > > > > > > > > > > > > > > Seems unlikely though! + we've not yet seen it on the other chips that > > > > > > > errata effects (not that that means much). > > > > > > > > > > > > If you can reproduce quickly, might be worth trying anyway... > > > > > > > > > > > > Thanx, Paul > > > > > Errata fix is running already and was for all those tests. > > > > > > > > I was afraid of that... ;-) > > > It's a pretty rare errata it seems. Not actually managed to catch > > > one yet. > > > > > > > > > I'll have a dig into the timers today and see where I get to. > > > > > > > > Look forward to seeing what you find! > > > Nothing obvious turning up other than we don't seem to have issue > > > when we aren't running hrtimers. > > > > > > On a plus side I just got a report that it is effecting our d03 > > > boards which is good on the basis I couldn't tell what the difference > > > could be wrt to this issue! > > > > > > It indeed looks like we are consistently missing a timer before > > > the rcu splat occurs. > > > > And for my part, my tests with CONFIG_HZ_PERIODIC=y and > > CONFIG_RCU_FAST_NO_HZ=n showed roughly the same failure rate > > as other runs. > > > > Missing a timer can most certainly give RCU severe heartburn! ;-) > > Do you have what you need to track down the missing timer? > > Not managed to make much progress yet. Turning on any additional tracing > in that area seems to make the issue stop happening or at least > occur very infrequently. Which certainly makes it 'fun' to find. > > As a long shot I applied a locking fix from another reported issue that > was causing rcu stalls and it seemed good for much longer, but > eventually still occurred. > > (from the thread rcu_sched stall while waiting in csd_lock_wait()) On the perhaps unlikely off-chance that it helps locate something, here is a patch that adds a trace_printk() to check how long a CPU believes that it can sleep when going idle. The thought is to check to see if a CPU with a timer set to expire in one jiffy thinks that can sleep for (say) 30 seconds. Didn't find anything for my problem, but I believe that yours is different, so... Thanx, Paul ------------------------------------------------------------------------ commit 33103e7b1f89ef432dfe3337d2a6932cdf5c1312 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Date: Mon Aug 14 08:54:39 2017 -0700 EXP: Trace tick return from tick_nohz_stop_sched_tick Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index c7a899c5ce64..7358a5073dfb 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -817,6 +817,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, * (not only the tick). */ ts->sleep_length = ktime_sub(dev->next_event, now); + trace_printk("tick_nohz_stop_sched_tick: %lld\n", (tick - ktime_get()) / 1000); return tick; } -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
