On Fri, Mar 15, 2013 at 2:06 AM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Thu, Mar 14, 2013 at 5:24 PM, Stephane Eranian <eran...@google.com> wrote: >> >> I bet if you force the affinity of your perf record to be on >> a CPU other than CPU0, you will not get the crash. >> >> This is what I am seeing now. I appears on resume, >> CPU0 hotplug callbacks for perf_events are not invoked >> leaving DS_AREA MSR to 0. >> >> Can you confirm on your machine? > > I'm not even going to bother confirming it, because I think you're > right, and I think the reason is clear: the DS initialization code > uses the CPU_UP notifiers. > Ok, I instrumented the pebs_enable() function and I confirm that DS_AREA=0 on resume.
So what seems broken here for me is that on suspend, the cpu notifier ends up calling fini_debug_store() to clear DS_AREA for CPU0. But on resume, the same notifier does NOT call the init_debug_store(). I don't understand this asymmetry. You either do neither or you do both. > And that's sufficient for CPU hotplug, which is what suspend/resume > ends up doing for all but the boot CPU. But the boot CPU is not > hotplugged. > > Using CPU_UP notifiers is wrong, and they get called too late anyway. > > The code should use a real resume method. Or, better yet, just do it > right, and do it from __restore_processor_state(). > > Those f*cking CPU notifiers are a pain in the ass, and the tend to be > invariably broken, and they have their own idiotic hacks that are > equally broken (ie that x86_pmu_notifier() thing seems to make up its > own suspend/resume with > "x86_pmu.cpu_prepare/cpu_starting/cpu_dying/cpu_dead" things. > > I guess we could make the BP do a fake cpu notifier thing around the > suspend of the boot processor as well, but most of the per-CPU stuff > seems to be perfectly fine without it (ie mtrr, apic, etc etc all use > the suspend/resume infrastructure) and doesn't need that kind of > stuff. > > Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
