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

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Date:	Thu, 21 Feb 2013 00:09:46 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Tejun Heo <tj@...nel.org>, Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] posix-timer: don't call idr_find() w/ negative ID

On Wed, 20 Feb 2013, Andrew Morton wrote:
> On Wed, 20 Feb 2013 13:37:01 -0800
> Tejun Heo <tj@...nel.org> wrote:
> > hopefully with some comments.  That said, if I'm grepping it right,
> > all archs define timer_t as int, so maybe we're just being paranoid.
> > 
> 
> 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...

First of all the compiler should warn you about the truncation. And
aside of that:

+ BUILD_BUG_ON(sizeof(timer_t) != sizeof(int));

and then we can worry about that esoteric architecture when that thing
triggers?

Aside of that, due to the pending checkpoint/restore stuff this user
might be gone in the near future.

Thanks,

	tglx

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