Hi! > > >>The second bug, is that for the halt case at least, > > >>nobody waits for the other CPU to actually halt > > >>before continuing.. so we sometimes enter the shutdown > > >>code while other CPUs are still active. > > >> > > >>This causes some machines to hang at shutdown, > > >>unless CPU_HOTPLUG is configured and takes them offline > > >>before we get here. > > > > > >I'm guessing there's a reason it doesn't pass '1' as the last argument, > > >because that would fix that issue? > > > > Undoubtedly -- perhaps the called CPU halts, and therefore cannot reply. :) > > Uhm yes, I guess stop_this_cpu() does exactly what the name implies :-) > > > But some kind of pre-halt ack, perhaps plus a short delay by the caller > > after receipt of the ack, would probably suffice to kill that bug. > > > > But I really haven't studied this code enough to know, > > other than that it historically has been a sticky area > > to poke around in. > > Something like this will close the window to right up until the point > where the other CPUs have 'almost' called halt(). Now I took a look at context... why not simply use same trick swsusp uses, and do a hot unplug of all cpus at the end of shutdown? > > diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c > index 5398385..94ec9bf 100644 > --- a/arch/x86/kernel/smp.c > +++ b/arch/x86/kernel/smp.c > @@ -155,8 +155,9 @@ static void stop_this_cpu(void *dummy) > /* > * Remove this CPU: > */ > - cpu_clear(smp_processor_id(), cpu_online_map); > disable_local_APIC(); > + cpu_clear(smp_processor_id(), cpu_online_map); > + smp_wmb(); > if (hlt_works(smp_processor_id())) > for (;;) halt(); > for (;;); > @@ -175,6 +176,12 @@ static void native_smp_send_stop(void) > > local_irq_save(flags); > smp_call_function(stop_this_cpu, NULL, 0, 0); > + > + while (cpus_weight(cpu_online_map) > 1) { > + cpu_relax(); > + smp_rmb(); > + } > + > disable_local_APIC(); > local_irq_restore(flags); > } -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html