[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 16:28, 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). -Stefan > > Juergen > Attachment:
signature.asc _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |