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

[Pavel Machek]

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 âswsusp_show_speedâ:
>   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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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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