Messages in this thread | | | Date | Mon, 10 Oct 2011 08:53:33 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC][PATCH] x86, reboot: use NMI instead of REBOOT_VECTOR to stop cpus |
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* Don Zickus <dzickus@redhat.com> wrote:
> --- a/arch/x86/kernel/smp.c > +++ b/arch/x86/kernel/smp.c > @@ -28,6 +28,7 @@ > #include <asm/mmu_context.h> > #include <asm/proto.h> > #include <asm/apic.h> > +#include <asm/nmi.h> > /* > * Some notes on x86 processor bugs affecting SMP operation: > * > @@ -147,6 +148,57 @@ void native_send_call_func_ipi(const struct cpumask *mask) > free_cpumask_var(allbutself); > } > > +static int stopping_cpu;
Is access to this variable sufficiently serialized by all callpaths of stop_other_cpus()?
> + > +static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs) > +{ > + /* We are registerd on stopping cpu too, avoid spurious NMI */ > + if (raw_smp_processor_id() == stopping_cpu) > + return NMI_HANDLED; > + > + stop_this_cpu(NULL); > + > + return NMI_HANDLED; > +} > + > +static void native_nmi_stop_other_cpus(int wait) > +{ > + unsigned long flags; > + unsigned long timeout; > + > + if (reboot_force) > + return; > + > + /* > + * Use an own vector here because smp_call_function > + * does lots of things not suitable in a panic situation. > + */ > + if (num_online_cpus() > 1) { > + stopping_cpu = safe_smp_processor_id(); > + > + if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback, > + NMI_FLAG_FIRST, "smp_stop")) > + return; /* return what? */ > + > + /* sync above data before sending NMI */ > + wmb(); > + > + apic->send_IPI_allbutself(NMI_VECTOR); > + > + /* > + * Don't wait longer than a second if the caller > + * didn't ask us to wait. > + */ > + timeout = USEC_PER_SEC; > + while (num_online_cpus() > 1 && (wait || timeout--)) > + udelay(1); > + } > + > + local_irq_save(flags); > + disable_local_APIC(); > + local_irq_restore(flags); > +} > + > /* > * this function calls the 'stop' function on all other CPUs in the system. > */ > @@ -159,7 +211,7 @@ asmlinkage void smp_reboot_interrupt(void) > irq_exit(); > } > > -static void native_stop_other_cpus(int wait) > +static void native_irq_stop_other_cpus(int wait) > { > unsigned long flags; > unsigned long timeout; > @@ -229,7 +281,7 @@ struct smp_ops smp_ops = { > .smp_prepare_cpus = native_smp_prepare_cpus, > .smp_cpus_done = native_smp_cpus_done, > > - .stop_other_cpus = native_stop_other_cpus, > + .stop_other_cpus = native_nmi_stop_other_cpus, > .smp_send_reschedule = native_smp_send_reschedule, > > .cpu_up = native_cpu_up,
I'd be fine about this if you also aded some sort of CONFIG_KERNEL_DEBUG dependent test facility that did a "send NMI to all CPUs and check that they truly arrive" non-destructive test.
That would at least give people an automatic way to test it without waiting for the first crash of their kernel.
Thanks,
Ingo
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