linux-kernel - Re: [PATCH] x86: fix hpet timer reinit for x86

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Message-ID: <20090204134933.GC17024@elte.hu>
Date:	Wed, 4 Feb 2009 14:49:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kirill Korotaev <dev@...nvz.org>
Subject: Re: [PATCH] x86: fix hpet timer reinit for x86_64


* Pavel Emelyanov <xemul@...nvz.org> 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@...nvz.org>
> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

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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