On 09/24/2012 11:49 PM, Borislav Petkov wrote: > On Mon, Sep 24, 2012 at 08:16:50PM +0200, Conny Seidel wrote: >> Hi, >> >> On Mon, 24 Sep 2012 16:36:09 +0200 >> Borislav Petkov <bp@xxxxxxxxx> wrote: >>> [ … ] >>> >>> Conny, would you test pls? >> >> 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. And, speaking of hotplug callbacks, on a slightly different note, I see one defined as ratelimit_handler(), which calls writeback_set_ratelimit() for *every single* state change in the hotplug sequence! Is that really intentional? num_online_cpus() changes its value only -once- for every hotplug :-) Regards, Srivatsa S. Bhat -- 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>