Subject: Re: [PATCH -tip] remove the BKL: Replace BKL in mount/umount
 syscalls with a mutex
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Ingo Molnar <mingo@elte.hu>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
       Alessio Igor Bogani <abogani@texware.it>,
       Alexander Viro <viro@ftp.linux.org.uk>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>, Jonathan Corbet <corbet@lwn.net>,
       Linus Torvalds <torvalds@linux-foundation.org>
In-Reply-To: <20090417165643.GL8253@elte.hu>
References: <1239892078-6039-1-git-send-email-abogani@texware.it>
	 <20090416160645.GB17804@elte.hu>
	 <20090416235649.GF26366@ZenIV.linux.org.uk>
	 <20090417000142.GF21405@elte.hu>
	 <20090417001345.GH26366@ZenIV.linux.org.uk>
	 <20090417002744.GB29630@elte.hu>
	 <20090417003805.GI26366@ZenIV.linux.org.uk> <20090417165643.GL8253@elte.hu>
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Date: Fri, 17 Apr 2009 19:04:45 +0200
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On Fri, 2009-04-17 at 18:56 +0200, Ingo Molnar wrote:

> Stupid question regarding c): wouldnt such data structures go via 
> the VFS - which you said was free of BKL constraints? Or are there 
> interconnected private data structures between certain types of 
> closely related filesystems that the VFS does not know about? (and 
> hence might have BKL assumptions)

The VFS is stuffed with ->private like pointers for filesystems to flesh
out, and I could well imagine some implicit serialization between the
various (4?) VFS hooks that are currently still under BKL.

Anyway, it seems quite clear that the first thing is to push the current
BKL usage down into the filesystems -- which should be somewhat
straight-forward.

After that it really comes down to picking off these filesystems one at
a time, which will really need a proper audit, there just ain't a proper
substitute for thinking ;-)

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