On Mon, 3 Oct 2016, Prarit Bhargava wrote: > BUG: unable to handle kernel paging request at 0000000000841f1f > IP: [<ffffffff81014ec4>] uncore_change_context+0xd4/0x180 ... > [<ffffffff81015a60>] ? uncore_cpu_starting+0x130/0x130 > [<ffffffff81015acc>] uncore_event_cpu_online+0x6c/0x80 > [<ffffffff8108e819>] cpuhp_invoke_callback+0x49/0x100 > [<ffffffff8108ead1>] cpuhp_thread_fun+0x41/0x100 > [<ffffffff810b054f>] smpboot_thread_fn+0x10f/0x160 > [<ffffffff810b0440>] ? sort_range+0x30/0x30 > [<ffffffff810accd8>] kthread+0xd8/0xf0 > [<ffffffff816ff4bf>] ret_from_fork+0x1f/0x40 > [<ffffffff810acc00>] ? kthread_park+0x60/0x60 > arch/x86/events/intel/uncore.c: > 1137 static void uncore_change_type_ctx(struct intel_uncore_type *type, int old_ cpu, > 1138 int new_cpu) > 1139 { > 1140 struct intel_uncore_pmu *pmu = type->pmus; > 1141 struct intel_uncore_box *box; > 1142 int i, pkg; > 1143 > 1144 pkg = topology_logical_package_id(old_cpu < 0 ? new_cpu : old_cpu); > 1145 for (i = 0; i < type->num_boxes; i++, pmu++) { > 1146 box = pmu->boxes[pkg]; > > pmu->boxes[pkg] is garbage because pkg was returned as 0xffff. And that's what needs to be fixed in the first place. > This patch adds the missing generic_processor_info() to > prefill_possible_map() to ensure the initialization of the boot cpu is > correct. > This results in smp_init_package_map() having correct data and > properly setting the package map for the hotplugged boot cpu, which in > turn resolves the kdump kernel panic on physically hotplugged cpus. While it is the right thing to initialize the package map in that case, it still papers over a robustness issue in the uncore code, which needs to be fixed first. > [2] prefill_possible_map() is called before smp_store_boot_cpu_info(). > The comment beside the call to smp_store_boot_cpu_info() states that the > completed call results in "Final full version of the data". I'm not sure what that [2] here means and I cannot figure out the meaning of this sentence either. This changelog is incomprehensible in general and more a "oh look how I decoded this problem" report than something which clearly describes the problem at hand, the root cause and the fix. The latter wants a understandable explanation why prefill_possible_map() is the right place to do this. > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 4296beb8fdd3..d1272febc13b 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -1406,9 +1406,18 @@ __init void prefill_possible_map(void) > { > int i, possible; > > - /* no processor from mptable or madt */ > - if (!num_processors) > - num_processors = 1; > + /* No boot processor was found in mptable or ACPI MADT */ > + if (!num_processors) { > + /* Make sure boot cpu is enumerated */ > + if (apic->cpu_present_to_apicid(0) == BAD_APICID && > + apic->apic_id_valid(boot_cpu_physical_apicid)) > + generic_processor_info(boot_cpu_physical_apicid, > + apic_version[boot_cpu_physical_apicid]); > + if (!num_processors) { > + pr_warn("CPU 0 not enumerated in mptable or ACPI MADT\n"); > + num_processors = 1; And in this case we end up with the same problem, right? Thanks, tglx