Re: [PATCH] x86: fix hpet timer reinit for x86_64

From: Ingo Molnar
Date: Wed Feb 04 2009 - 08:49:55 EST



* Pavel Emelyanov <xemul@xxxxxxxxxx> wrote:

> There's a small problem with hpet_rtc_reinit function - it checks
> for the
> hpet_readl(HPET_COUNTER) - hpet_t1_cmp > 0
> to continue increasing both the HPET_T1_CMP (register) and the
> hpet_t1_cmp (variable).
>
> But since the HPET_COUNTER is always 32-bit, if the hpet_t1_cmp
> is 64-bit this condition will always be FALSE once the latter hits
> the 32-bit boundary, and we can have a situation, when we don't
> increase the HPET_T1_CMP register high enough.
>
> The result - timer stops ticking, since HPET_T1_CMP becomes less,
> than the COUNTER and never increased again.
>
> The solution is to cut the upper 32-bit from the hpet_t1_cmp
> variable to make the comparison to HPET_COUNTER correct.
>
> Reported-by: Kirill Korotaev <dev@xxxxxxxxxx>
> Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxx>

applied to tip/timers/urgent, thanks Pavel!

I'm wondering, what symptoms were seen due to the bug? Did system time stop,
or did it become erratic, or were there outright lockups?

Ingo
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