[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 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. -Stefan > > Juergen > >> >> >>> + { >>> + ret = 0; >>> + break; >>> + } >>> + } >>> + } >>> + if ( !ret ) >>> cpumask_set_cpu(cpu, &cpupool_locked_cpus); >>> spin_unlock(&cpupool_lock); >>> >>> >>> >>> Juergen > Attachment:
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