On Wed, 8 Aug 2007 16:17:19 -0700
Aaron Durbin <[email protected]> wrote:
> In setup_APIC_timer with the HPET in use, a condition can arise while
> waiting for the next irq slice to expire on the HPET which will either
> cause an NMI watchdog to fire or a 3 minute busy loop if the NMI
> watchdog is disabled.
>
> The HPET comparator and the counter keep incrementing during its normal
> operation. When a comparison event fires the comparator will increment
> by the designated period. If the HPET trigger occurs right after
> the 'int trigger = hpet_readl(HPET_T0_CMP);' line, we will will spin
> for up to 3 minutes (with a clock of 25MHz) waiting for the HPET
> counter to wrap around. However, when the NMI watchdog is enabled the
> NMI watchdog will detect a lockup and reboot the machine. This
> scenario can be exasperated by the presence of an SMI which will
> increase the window of opportunity for the condition to occur.
>
> The fix is to wait for the compartor to change which signals the
> end of the tick slice.
>
> ---
>
> The last patch had a typo in the diff which really would cause the
> problem state above. Sorry.
>
> diff --git a/arch/x86_64/kernel/apic.c b/arch/x86_64/kernel/apic.c
> index 900ff38..06797e2 100644
> --- a/arch/x86_64/kernel/apic.c
> +++ b/arch/x86_64/kernel/apic.c
> @@ -791,10 +791,12 @@ static void setup_APIC_timer(unsigned in
>
> /* wait for irq slice */
> if (hpet_address && hpet_use_timer) {
> + /*
> + * Wait for the comparator value to change which signals that
> + * the tick slice has expired.
> + */
> int trigger = hpet_readl(HPET_T0_CMP);
> - while (hpet_readl(HPET_COUNTER) >= trigger)
> - /* do nothing */ ;
> - while (hpet_readl(HPET_COUNTER) < trigger)
> + while (trigger == hpet_readl(HPET_T0_CMP))
> /* do nothing */ ;
> } else {
> int c1, c2;
but, but. Didn't this get fixed by
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc2/2.6.23-rc2-mm1/broken-out/fix-hpet-init-race.patch
?
-
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