On Tue, Sep 25, 2012 at 12:18:46AM +0530, Srivatsa S. Bhat wrote: > >> Sure thing. > >> Out of ~25 runs I only triggered it once, without the patch the > >> trigger-rate is higher. > >> > >> [ 55.098249] Broke affinity for irq 81 > >> [ 55.105108] smpboot: CPU 1 is now offline > >> [ 55.311216] smpboot: Booting Node 0 Processor 1 APIC 0x11 > >> [ 55.333022] LVT offset 0 assigned for vector 0x400 > >> [ 55.545877] smpboot: CPU 2 is now offline > >> [ 55.753050] smpboot: Booting Node 0 Processor 2 APIC 0x12 > >> [ 55.775582] LVT offset 0 assigned for vector 0x400 > >> [ 55.986747] smpboot: CPU 3 is now offline > >> [ 56.193839] smpboot: Booting Node 0 Processor 3 APIC 0x13 > >> [ 56.212643] LVT offset 0 assigned for vector 0x400 > >> [ 56.423201] Got negative events: -25 > > > > I see it: > > > > __percpu_counter_sum does for_each_online_cpu without doing > > get/put_online_cpus(). > > > > Maybe I'm missing something, but that doesn't immediately tell me > what's the exact source of the bug.. Note that there is a hotplug > callback percpu_counter_hotcpu_callback() that takes the same > fbc->lock before updating/resetting the percpu counters of offline > CPU. So, though the synchronization is a bit weird, I don't > immediately see a problematic race condition there. Well, those oopses both happen when a cpu comes online. According to when percpu_counter_hotcpu_callback is run (at CPU_DEAD) then those percpu variables should have correctly updated values. So there has to be some other case where we read garbage which is a negative value - otherwise we wouldn't be seeing the debug output. For example, look at the log output above: we bring down cpu 3 just to bring it right back online. So there has to be something fishy along that codepath... Hmm. -- Regards/Gruss, Boris. Advanced Micro Devices GmbH Einsteinring 24, 85609 Dornach GM: Alberto Bozzo Reg: Dornach, Landkreis Muenchen HRB Nr. 43632 WEEE Registernr: 129 19551 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>