[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Shutdown panic in disable_nonboot_cpus after cpupool-numa-split
On 07.07.2014 16:43, Stefan Bader wrote: > On 07.07.2014 16:28, Juergen Gross wrote: >> On 07/07/2014 04:08 PM, Stefan Bader wrote: >>> On 07.07.2014 15:03, Jürgen Groß wrote: >>>> On 07/07/2014 02:49 PM, Stefan Bader wrote: >>>>> On 07.07.2014 14:38, Jürgen Groß wrote: >>>>>> On 07/07/2014 02:00 PM, Andrew Cooper wrote: >>>>>>> On 07/07/14 12:33, Stefan Bader wrote: >>>>>>>> I recently noticed that I get a panic (rebooting the system) on >>>>>>>> shutdown in >>>>>>>> some >>>>>>> > cases. This happened only on my AMD system and also not all the >>>>>>> time. >>>>>>> Finally >>>>>>> > realized that it is related to the use of using cpupool-numa-split >>>>>>> > (libxl with xen-4.4 maybe, but not 100% sure 4.3 as well). >>>>>>> > >>>>>>> > What happens is that on shutdown the hypervisor runs >>>>>>> disable_nonboot_cpus which >>>>>>> > call cpu_down for each online cpu. There is a BUG_ON in the code >>>>>>> for >>>>>>> the case of >>>>>>> > cpu_down returning -EBUSY. This happens in my case as soon as the >>>>>>> first cpu that >>>>>>> > has been moved to pool-1 by cpupool-numa-split is attempted. The >>>>>>> error is >>>>>>> > returned by running the notifier_call_chain and I suspect that ends >>>>>>> up calling >>>>>>> > cpupool_cpu_remove which always returns EBUSY for cpus not in >>>>>>> pool0. >>>>>>> > >>>>>>> > I am not sure which end needs to be fixed but looping over all >>>>>>> online >>>>>>> cpus in >>>>>>> > disable_nonboot_cpus sounds plausible. So maybe the check for >>>>>>> pool-0 in >>>>>>> > cpupool_cpu_remove is wrong...? >>>>>>> > >>>>>>> > -Stefan >>>>>>> >>>>>>> Hmm yes - this looks completely broken. >>>>>>> >>>>>>> cpupool_cpu_remove() only has a single caller which is from cpu_down(), >>>>>>> and will unconditionally fail for cpus outside of the default pool. >>>>>>> >>>>>>> It is not obvious at all how this is supposed to work, and the comment >>>>>>> beside cpupool_cpu_remove() doesn't help. >>>>>>> >>>>>>> Can you try the following (only compile tested) patch, which looks >>>>>>> plausibly like it might DTRT. The for_each_cpupool() is a little nastly >>>>>>> but there appears to be no cpu_to_cpupool mapping available. >>>>>> >>>>>> Your patch has the disadvantage to support hot-unplug of the last cpu in >>>>>> a cpupool. The following should work, however: >>>>> >>>>> Disadvantage and support sounded a bit confusing. But I think it means >>>>> hot-unplugging the last cpu of a pool is bad and should not be working. >>>> >>>> Correct. >>>> >>>>> >>>>>> >>>>>> diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c >>>>>> index 4a0e569..73249d3 100644 >>>>>> --- a/xen/common/cpupool.c >>>>>> +++ b/xen/common/cpupool.c >>>>>> @@ -471,12 +471,24 @@ static void cpupool_cpu_add(unsigned int cpu) >>>>>> */ >>>>>> static int cpupool_cpu_remove(unsigned int cpu) >>>>>> { >>>>>> - int ret = 0; >>>>>> + int ret = -EBUSY; >>>>>> + struct cpupool **c; >>>>>> >>>>>> spin_lock(&cpupool_lock); >>>>>> - if ( !cpumask_test_cpu(cpu, cpupool0->cpu_valid)) >>>>>> - ret = -EBUSY; >>>>>> + if ( cpumask_test_cpu(cpu, cpupool0->cpu_valid) ) >>>>>> + ret = 0; >>>>>> else >>>>>> + { >>>>>> + for_each_cpupool(c) >>>>>> + { >>>>>> + if ( cpumask_test_cpu(cpu, (*c)->cpu_suspended ) ) >>>>> >>>>> The rest seems to keep the semantics the same as before (though does that >>>>> mean >>>>> unplugging the last cpu of pool-0 is ok?) But why testing for suspended >>>>> here to >>>>> succeed (and not valid)? >>>> >>>> Testing valid would again enable to remove the last cpu of a cpupool in >>>> case of hotplugging. cpu_suspended is set if all cpus are to be removed >>>> due to shutdown, suspend to ram/disk, ... >>> >>> Ah, ok. Thanks for the detail explanation. So I was trying this change in >>> parallel and can confirm that it gets rid of the panic on shutdown. But >>> when I >>> try to offline any cpu in pool1 (if echoing 0 into >>> /sys/devices/xen_cpu/xen_cpu? >>> is the correct method) I always get EBUSY. IOW I cannot hot-unplug any cpu >>> that >>> is in a pool other than 0. It does only work after removing it from pool1, >>> then >>> add it to pool0 and then echo 0 into online. >> >> That's how it was designed some years ago. I don't want to change the >> behavior in the hypervisor. Adding some tool support could make sense, >> however. > > Ok, so in that case everything works as expected and the change fixes the > currently broken shutdown and could be properly submitted for inclusion (with > my > tested-by). > Is this needing something from my side to do? I could re-submit the whole patch but it since it is Juergen's work it felt a little rude to do so. -Stefan Attachment:
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