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SubjectRe: [PATCH] x86 apic: Ack all pending irqs when crashed/on kexec
On 03/08/2010 01:17 PM, Thomas Renninger wrote:
> From: Kerstin Jonsson<kerstin.jonsson@ericsson.com>
>
> When the SMP kernel decides to crash_kexec() the local APICs may have
> pending interrupts in their vector tables.
> The setup routine for the local APIC has a deficient mechanism for
> clearing these interrupts, it only handles interrupts that has already
> been dispatched to the local core for servicing (the ISR register)
> safely, it doesn't consider lower prioritized queued interrupts stored
> in the IRR register.
>
> If you have more than one pending interrupt within the same 32 bit word
> in the LAPIC vector table registers you may find yourself entering the
> IO APIC setup with pending interrupts left in the LAPIC. This is a
> situation for wich the IO APIC setup is not prepared. Depending of
> what/which interrupt vector/vectors are stuck in the APIC tables your
> system may show various degrees of malfunctioning.
> That was the reason why the check_timer() failed in our system, the
> timer interrupts was blocked by pending interrupts from the old kernel
> when routed trough the IO APIC.
>
> Additional comment from Jiri Bohac:
> ==============
> If this should go into stable release,
> I'd add some kind of limit on the number of iterations, just to be safe from
> hard to debug lock-ups:
>
> +if (loops++> MAX_LOOPS) {
> + printk("LAPIC pending clean-up")
> + break;
> +}
> while (queued);
>
> with MAX_LOOPS something like 1E9 this would leave plenty of time for the
> pending IRQs to be cleared and would and still cause at most a second of delay
> if the loop were to lock-up for whatever reason.
> ==============
>
> From trenn@suse.de:
> V2: Use tsc if avail to bail out after 1 sec due to possible virtual apic_read
> calls which may take rather long (suggested by: Avi Kivity<avi@redhat.com>)
> If no tsc is available bail out quickly after cpu_khz, if we broke out too
> early and still have irqs pending (which should never happen?) we still
> get a WARN_ON...
>
>
>
> @@ -1151,8 +1152,12 @@ static void __cpuinit lapic_setup_esr(void)
> */
> void __cpuinit setup_local_APIC(void)
> {
> - unsigned int value;
> - int i, j;
> + unsigned int value, queued;
> + int i, j, acked = 0;
> + unsigned long long tsc = 0, ntsc, max_loops = cpu_khz;
> +
> + if (cpu_has_tsc)
> + rdtscll(ntsc);
>
>
>

...

> + if (cpu_has_tsc) {
> + rdtscll(ntsc);
> + max_loops = (cpu_khz<< 10) - (ntsc - tsc);
>

Since max_loops is unsigned, this will always be positive.

> + } else
> + max_loops--;
> + } while (queued&& max_loops> 0);
> + WARN_ON(!max_loops);
>

So the loop never terminates unless queued becomes true.

--
error compiling committee.c: too many arguments to function



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