Re: [patch] sys_epoll_wait() timeout saga ...

[Willy Tarreau <willy@w.ods.org>]

Hi Davide,

On Fri, Sep 23, 2005 at 11:13:30AM -0700, Davide Libenzi wrote:
> 
> The sys_epoll_wait() function was not handling correctly negative 
> timeouts (besides -1), and like sys_poll(), was comparing millisec to 
> secs in testing the upper timeout limit.
> 
> 
> Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
> 
> 
> - Davide

> --- a/fs/eventpoll.c	2005-09-23 10:56:57.000000000 -0700
> +++ b/fs/eventpoll.c	2005-09-23 11:00:06.000000000 -0700
> @@ -1507,7 +1507,7 @@
>  	 * and the overflow condition. The passed timeout is in milliseconds,
>  	 * that why (t * HZ) / 1000.
>  	 */
> -	jtimeout = timeout == -1 || timeout > (MAX_SCHEDULE_TIMEOUT - 1000) / HZ ?
> +	jtimeout = timeout < 0 || (timeout / 1000) >= (MAX_SCHEDULE_TIMEOUT / HZ) ?
>  		MAX_SCHEDULE_TIMEOUT: (timeout * HZ + 999) / 1000;

Here, I'm not certain that gcc will optimize the divide. It would be better
anyway to write this which is equivalent, and a pure integer comparison :

+	jtimeout = timeout < 0 || timeout >= 1000 * MAX_SCHEDULE_TIMEOUT / HZ ?
>  		MAX_SCHEDULE_TIMEOUT: (timeout * HZ + 999) / 1000;

gcc will also spit a warning if the constant is too big for an int,
depending on MAX_SCHEDULE_TIMEOUT and HZ, while in the previous case,
it would remain silent, and possibly, timeout/1000 would never reach
the limit.

Regards,
Willy