linux-kernel - Re: [PATCH] hangcheck-timer is broken on x86

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Message-Id: <20100326142423.1334d407.akpm@linux-foundation.org>
Date:	Fri, 26 Mar 2010 14:24:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yury Polyanskiy <ypolyans@...nceton.edu>
Cc:	Joel Becker <joel.becker@...cle.com>, linux-kernel@...r.kernel.org,
	john stultz <johnstul@...ibm.com>,
	Jan Glauber <jan.glauber@...ibm.com>
Subject: Re: [PATCH] hangcheck-timer is broken on x86

On Tue, 23 Mar 2010 23:36:11 -0400
Yury Polyanskiy <ypolyans@...nceton.edu> wrote:

> The drivers/char/hangcheck-timer.c is doubly broken. First, the
> following line overflows unsigned long:
> # define TIMER_FREQ (HZ*loops_per_jiffy)
> 
> Second, and more importantly, loops_per_jiffy has little to do with the conversion from the
> the time scale of get_cycles() (aka rdtsc) to the time scale of jiffies.

It's a bit odd to have a driver be this broken on x86_32 for five years
without anyone noticing.  What are the user-visible effects of these
shortcomings?

Also, please do send us a Signed-off-by: for this patch, as explained
in Documentation/SubmittingPatches, thanks.

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