linux-kernel - Re: [PATCH 1/4] lockdep: lock_set

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Date:	Mon, 07 Nov 2011 13:34:39 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	linux-kernel@...r.kernel.org, sergey.senozhatsky@...il.com,
	bp@...en8.de, Ingo Molnar <mingo@...e.hu>,
	Tejun Heo <tj@...nel.org>, David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 1/4] lockdep: lock_set_subclass() fix

On Fri, 2011-11-04 at 17:26 +0800, Yong Zhang wrote:
> Since commit f59de89 [lockdep: Clear whole lockdep_map on initialization],
> lockdep_init_map() will clear all the struct. But it will break
> lock_set_class()/lock_set_subclass(). A typical race condition
> is like below:

This is a horridly ugly patch, why not simply revert that memset commit?
I really can't see the point of that, and keeping the name/key pointers
around (which can only be over-written with the same values, right?)
would also cure the problem.

Sadly the changelog is completely devoid of useful information (which is
my own damn fault, I should never have accepted the patch in that form),
so I can't actually comment on what it was supposed to fix.

Arguably kmemcheck is on crack or so since both name and key pointers
should be in .data so there cannot be a leak by copying the thing over.
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