linux-kernel - Re: [PATCH] posix-timer: don't call idr

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Message-ID: <20130220220823.GH3570@htj.dyndns.org>
Date:	Wed, 20 Feb 2013 14:08:23 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] posix-timer: don't call idr_find() w/ negative ID

On Wed, Feb 20, 2013 at 02:05:51PM -0800, Andrew Morton wrote:
> Sure, it's unlikely to cause a problem in practice.  Maybe five years
> from now, after idr has been cleaned up and switched to 64-bit, we've
> left a little hand grenade for someone.  It would be good to
> future-safe it in some fashion.
> 
> I wonder if we should add some generic facility to handle this:
> 
> /*
>  * Query whether an unsigned type is `negative' when we don't know its size
>  */
> #define msb_is_set(v)	{ implementation goes here ;) }
> 
> Maybe not justified, dunno...

The thing is it's not only about MSB.  Any bits beyond 1 << 31 are
problematic, so we want a range test.

Thanks.

-- 
tejun
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