linux-kernel - Re: RFC: Reproducible oops with lockdep on count_matching

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Message-Id: <1194001120.27652.353.camel@twins>
Date:	Fri, 02 Nov 2007 11:58:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michael Wu <flamingice@...rmilk.net>
Cc:	"Luis R. Rodriguez" <mcgrof@...il.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"John W. Linville" <linville@...driver.com>,
	Ingo Molnar <mingo@...hat.com>,
	Johannes Berg <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org
Subject: Re: RFC: Reproducible oops with lockdep on count_matching_names()

On Thu, 2007-11-01 at 19:26 -0400, Michael Wu wrote:
> On Thursday 01 November 2007 15:17:16 Luis R. Rodriguez wrote:
> > mcgrof@...o:~/devel/wireless-2.6$ git-describe
> > v2.6.24-rc1-146-g2280253
> >
> > So I hit segfault with lockdep on count_matching_names() on the
> > strcmp() multiple times now. This is reproducible and with different
> > wireless drivers.
> >
> I've found the problem. It appears to be in lockdep. struct lock_class has a 
> const char *name field which points to a statically allocated string that 
> comes from the code which uses the lock. If that code/string is in a module 
> and gets unloaded, the pointer in |name| is no longer valid. Next time this 
> field is dereferenced (count_matching_names, in this case), we crash.
> 
> The following patch fixes the issue but there's probably a better way.

Thanks, and indeed. From my understanding lockdep_free_key_range()
should destroy all classes of a module on module unload.

So I'm not quite sure what has gone wrong here..


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