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Subject: Re: [PATCH] fs: sys_poll with timeout -1 bug fix
From: Matt Helsley <matthltc@us.ibm.com>
To: frode isaksen <frode.isaksen@gmail.com>
Cc: Andrew Morton <akpm@osdl.org>, Nishanth Aravamudan <nacc@us.ibm.com>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Thu, 15 Jun 2006 14:13:29 -0700
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On Thu, 2006-06-15 at 17:33 +0200, frode isaksen wrote:
> From: Frode Isaksen <frode.isaksen@gmail.com>
> 
> If you do a poll() call with timeout -1, the wait will be a big  
> number (depending on HZ)  instead of infinite wait, since -1 is  
> passed to the msecs_to_jiffies function.
> 
> Signed-off-by: Frode Isaksen <frode.isaksen@gmail.com>
> 
> ---
> --- linux-2.6.16.20/fs/select.c.orig.c	2006-06-05 19:18:23.000000000  
> +0200
> +++ linux-2.6.16.20/fs/select.c	2006-06-15 14:20:47.000000000 +0200
> @@ -699,9 +699,9 @@ out_fds:
>   asmlinkage long sys_poll(struct pollfd __user *ufds, unsigned int  
> nfds,
>   			long timeout_msecs)
>   {
> -	s64 timeout_jiffies = 0;
> +	s64 timeout_jiffies;
> 
> -	if (timeout_msecs) {
> +	if (timeout_msecs > 0) {
>   #if HZ > 1000
>   		/* We can only overflow if HZ > 1000 */
>   		if (timeout_msecs / 1000 > (s64)0x7fffffffffffffffULL / (s64)HZ)
> @@ -709,6 +709,9 @@ asmlinkage long sys_poll(struct pollfd _
>   		else
>   #endif
>   			timeout_jiffies = msecs_to_jiffies(timeout_msecs);
> +	} else {
> +		/* Infinite (-1) or no (0) timeout */
> +		timeout_jiffies = timeout_msecs;

nit: The comment isn't quite right according to the poll manpage. Any
negative number represents an infinite timeout. I think you want:

+ 		/* Infinite (< 0) or no (0) timeout */

>   	}
> 
>   	return do_sys_poll(ufds, nfds, &timeout_jiffies);