linux-kernel - Re: [PATCH v2] kernel/power/hibernate.c: use 'u64' instead of 's64' to avoid warning

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Message-ID: <20140422072112.GB14108@amd.pavel.ucw.cz>
Date:	Tue, 22 Apr 2014 09:21:12 +0200
From:	Pavel Machek <pavel@....cz>
To:	Chen Gang <gang.chen.5i5j@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Guan Xuetao <gxt@...c.pku.edu.cn>, len.brown@...el.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2] kernel/power/hibernate.c: use 'u64' instead of
 's64' to avoid warning

On Tue 2014-04-22 09:29:20, 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.
> 
> Even if 'start' was really bigger than 'stop', it would print incorrect
> information, but for kernel, it still can continue, so use WARN_ON() is
> enough.
> 
> 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
> 
> 

Certainly better, but

> -	s64 elapsed_centisecs64;
> +	u64 elapsed_centisecs64;
>  	int centisecs;
>  	int k;
>  	int kps;
>  
>  	elapsed_centisecs64 = timeval_to_ns(stop) - timeval_to_ns(start);
> +	WARN_ON((s64)elapsed_centisecs64 < 0);
>  	do_div(elapsed_centisecs64, NSEC_PER_SEC / 100);
>  	centisecs = elapsed_centisecs64;

...do we need to do the WARN_ON()? Only result of underflow will be
very long elapsed time reported... that does not sound too
bad. ... and it will be quite obvious what went wrong.
									Pavel
-- 
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