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

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Message-ID: <20130220214346.GF3570@htj.dyndns.org>
Date:	Wed, 20 Feb 2013 13:43:46 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	akpm@...ux-foundation.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

Hey, Thomas.

On Wed, Feb 20, 2013 at 10:38:36PM +0100, Thomas Gleixner wrote:
> I can grumpily accept the patch below as a quick hack fix, which can
> go to stable as well, but not with such a patently misleading
> changelog.
> 
> The changelog wants to document, that this is not a proper fix at all
> and just a quick hack which can be nonintrusively applied to stable.

I'm not sure about what type timer_t can be but if it can actually be
u64 as Andrew suggests, we probably want a different test guarding it.

> > Note that the previous code was theoretically broken.  idr_find()
> > masked off the sign bit before performing lookup and if the matching
> > IDs were in use, it would have returned pointer for the incorrect
> > entry.
> 
> Brilliant code that. What's the purpose of having the idr id as an
> "int" and then masking off the sign bit instead of simply refusing
> negative id values in the idr code itself or simply making the id
> "unsigned int" ?

Beats me.  The code has been like that since the beginning.  One of
the many oddities of idr implementation.  Patch to remove MAX_IDR_MASK
is already queued in -mm w/ other idr updates.

Thanks.

-- 
tejun
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