linux-kernel - Re: [PATCH 23/23] clocksource tsc: add verify routine

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Message-ID: <20070131124300.GG1847@elte.hu>
Date:	Wed, 31 Jan 2007 13:43:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, johnstul@...ibm.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 23/23] clocksource tsc: add verify routine


* Daniel Walker <dwalker@...sta.com> wrote:

> I've included this as another user of the clocksource interface. I 
> don't see a usage for this across all achitectures. So a fully generic 
> version isn't needed.

well, this implementation is buggy in at least two ways:

firstly, it allows a circular verification dependency in highres+dyntick 
mode between the jiffies and tsc clocksources.

secondly, verification is not done while the system is booting up:

>  static void verify_tsc_freq(unsigned long unused)
>  {

[...]
> +	if (unlikely(system_state != SYSTEM_RUNNING))
> +		goto out_timer;

so we should just go with Thomas' patch:

  clocksource-add-verification-watchdog-helper.patch

which has been based on and tested on actual systems affected by these 
problems.

	Ingo
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