linux-kernel - Re: [PATCH] kill empty chardev open/release methods

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Message-ID: <11727.1211139999@vena.lwn.net>
Date:	Sun, 18 May 2008 13:46:39 -0600
From:	corbet@....net (Jonathan Corbet)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Jonathan Corbet <corbet@....net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kill empty chardev open/release methods 

Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> Actually it turns out you can introduce bugs doing this when the BKL is
> pushed down.
> 
> The problem is the methods are not NULL, they (with the lock pushed down
> are)
> 
> {
> 	lock_kernel();
> 	unlock_kernel();
> }
> 
> And we have drivers with setup code that does things in the wrong order
> but under the BKL. eg one I just fixed did
> 
> 	misc_register()
> 	init locks
> 	allocate memory
> 	do stuff
> 	return 0;

Hmph.

As it turns out, a misc driver will still be OK because the BKL has not
(yet) been pushed past misc_open().  What this does mean, though, is
that all of those empty and trivial open functions need to be
revisited.  I thought this looked too easy the first time through...

jon
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