linux-kernel - Re: [PATCH] kernel/power/hibernate.c: be sure of 'start' is not bigger than 'stop'

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Message-ID: <20140421200930.GA9880@amd.pavel.ucw.cz>
Date:	Mon, 21 Apr 2014 22:09:30 +0200
From:	Pavel Machek <pavel@....cz>
To:	Chen Gang <gang.chen.5i5j@...il.com>
Cc:	Guan Xuetao <gxt@...c.pku.edu.cn>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, len.brown@...el.com,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/power/hibernate.c: be sure of 'start' is not
 bigger than 'stop'

On Mon 2014-04-21 21:40:27, Chen Gang wrote:
> For do_div(), it need 'u64' type, which means the outside must be sure
> of 'start' is not bigger than 'stop', or it will report warning.
> 
> The related warning (with allmodconfig for unicore32):
> 
>     CC      kernel/power/hibernate.o
>   kernel/power/hibernate.c: In function ‘swsusp_show_speed’:
>   kernel/power/hibernate.c:237: warning: comparison of distinct pointer types lacks a cast
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>

>  {
> -	s64 elapsed_centisecs64;
> +	u64 elapsed_centisecs64;
>  	int centisecs;
>  	int k;
>  	int kps;
>  
>  	elapsed_centisecs64 = timeval_to_ns(stop) - timeval_to_ns(start);
> +	if ((s64)elapsed_centisecs64 < 0) {
> +		printk(KERN_ERR "PM: stop: %llu < start %llu\n",
> +			timeval_to_ns(stop), timeval_to_ns(start));
> +		return;
> +	}
>  	do_div(elapsed_centisecs64, NSEC_PER_SEC / 100);
>  	centisecs = elapsed_centisecs64;
>  	if (centisecs == 0)

Quite a lot of code to shut up warning in mostly debugging
function... is there alternative method of shutting it up? Have you
seen < 0 values in wild? Is it worth handing that situation?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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