Messages in this thread | | | Date | Wed, 08 Aug 2012 10:20:03 +0800 | From | Michael Wang <> | Subject | Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6 |
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On 08/07/2012 06:24 PM, Sasha Levin wrote: > On 08/07/2012 07:40 AM, John Stultz wrote: >> On 08/06/2012 11:28 AM, Sasha Levin wrote: >>> On 08/06/2012 08:20 PM, John Stultz wrote: >>>> On 08/06/2012 10:21 AM, John Stultz wrote: >>>>> On 08/05/2012 09:55 AM, Sasha Levin wrote: >>>>>> On 07/30/2012 03:17 PM, Avi Kivity wrote: >>>>>>> Possible causes: >>>>>>> - the APIC calibration in the guest failed, so it is programming too >>>>>>> low values into the timer >>>>>>> - it actually needs 1 us wakeups and then can't keep up (esp. as kvm >>>>>>> interrupt injection is slowing it down) >>>>>>> >>>>>>> You can try to find out by changing >>>>>>> arch/x86/kvm/lapic.c:start_lapic_timer() to impose a minimum wakeup of >>>>>>> (say) 20 microseconds which will let the guest live long enough for you >>>>>>> to ftrace it and see what kind of timers it is programming. >>>>>> I've kept trying to narrow it down, and found out It's triggerable using adjtimex(). >>>> Sorry, one more question: Could you provide details on how is it trigger-able using adjtimex? >>> It triggers after a while of fuzzing using trinity of just adjtimex ('./trinity --quiet -l off -cadjtimex'). >>> >>> Trinity is available here: http://git.codemonkey.org.uk/?p=trinity.git . >>> >>> Let me know if I can help further with reproducing this, I can probably copy over my testing environment to some other host if you'd like. >> >> Ok. Finally I *think* got it reproduced. (Had some trouble initially, as I think since the first time I ran it as a normal user, the socket cache isn't the same as if you run it the first time as root? Anyway, after doing a make clean and rebuilding it started to trigger). >> >> I'm not seeing the rcu stall message, but I do manage to trigger two other behaviors: a hard hang and a sort of zombie state where memory isn't properly being freed & everything starts segfaulting. So this may not be the exact same issue, but it triggers quickly as you described (within a few seconds of running trinity as root). >> >> It looks like both of these issues are caused by adjtimex(ADJ_SETOFFSET), which adds or subtracts a huge offset and that either goes negative or gets clamped to a ktime_t at KTIME_MAX (if you get clamped the system hangs, if it goes negative, the system barely functions, but sort of drags along). >> >> An updated version of my KTIME_MAX sanity checking patch to handle both of these conditions is below. >> >> Would you mind giving this patch a shot and letting me know if you still see problems? > > This fixes the problem for me. Thanks!
Could you please also try to reduce the CONFIG_RCU_CPU_STALL_TIMEOUT from 60 to 3 and see whether the rcu stall info will show again?(sorry I can't do it by my self since the stall info never appear in my sight...)
That will be very helpful as I suppose it is time to recover CONFIG_RCU_CPU_STALL_TIMEOUT to a reasonable value now ;-)
Regards, Michael Wang
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