linux-kernel - Re: [PATCH] fix jiffy calculations in calibrate_delay

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Message-ID: <4D525CA8.60604@suse.cz>
Date:	Wed, 09 Feb 2011 10:21:44 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tim Deegan <Tim.Deegan@...rix.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix jiffy calculations in calibrate_delay_direct to	
 handle overflow

On 02/09/2011 09:31 AM, Jan Beulich wrote:
> Fixes a hang when booting as dom0 under Xen, when jiffies can be
> quite large by the time the kernel init gets this far.

As I wrote this might happen if the boot till this point takes ~ 5
minutes because we start at -5 minutes.

That said, is this a candidate for stable? (If so, please CC stable.)

> Signed-off-by: Tim Deegan <Tim.Deegan@...rix.com>
> 
> !time_after() -> time_before_eq() as per suggestion from Jiri Slaby.
> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: Jeremy Fitzhardinge <jeremy@...p.org>
> 
> ---
>  init/calibrate.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> --- 2.6.38-rc4/init/calibrate.c
> +++ 2.6.38-rc4-calibrate-jiffy-overflow/init/calibrate.c
> @@ -66,7 +66,7 @@ static unsigned long __cpuinit calibrate
>  		pre_start = 0;
>  		read_current_timer(&start);
>  		start_jiffies = jiffies;
> -		while (jiffies <= (start_jiffies + 1)) {
> +		while (time_before_eq(jiffies, start_jiffies + 1)) {
>  			pre_start = start;
>  			read_current_timer(&start);
>  		}
> @@ -74,8 +74,8 @@ static unsigned long __cpuinit calibrate
>  
>  		pre_end = 0;
>  		end = post_start;
> -		while (jiffies <=
> -		       (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
> +		while (time_before_eq(jiffies, start_jiffies + 1 +
> +					       DELAY_CALIBRATION_TICKS)) {
>  			pre_end = end;
>  			read_current_timer(&end);
>  		}

thanks,
-- 
js
suse labs
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