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Date: Mon, 10 Oct 2011 08:53:33 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Don Zickus <dzickus@...hat.com>
Cc: Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Robert Richter <robert.richter@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
seiji.aguchi@....com, vgoyal@...hat.com, mjg@...hat.com,
tony.luck@...el.com, gong.chen@...el.com, satoru.moriya@....com,
avi@...hat.com
Subject: Re: [RFC][PATCH] x86, reboot: use NMI instead of REBOOT_VECTOR to
stop cpus
* Don Zickus <dzickus@...hat.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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