Date: Fri, 17 Apr 2009 02:01:42 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Alessio Igor Bogani <abogani@texware.it>,
       Alexander Viro <viro@ftp.linux.org.uk>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>, Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH -tip] remove the BKL: Replace BKL in mount/umount
	syscalls with a mutex
Message-ID: <20090417000142.GF21405@elte.hu>
References: <1239892078-6039-1-git-send-email-abogani@texware.it> <20090416160645.GB17804@elte.hu> <20090416235649.GF26366@ZenIV.linux.org.uk>
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* Al Viro <viro@ZenIV.linux.org.uk> wrote:

> remount is potentially nastier, but then it *is* nasty.  Again, 
> it's only per-fs stuff, so the obvious first step is taking BKL 
> down into the instances. It doesn't protect anything in VFS; all 
> uses are fs internal, so that'll take review of individual 
> filesystems.
> 
> NOTE: do not assume that code in fs/foo/* is correct; "it doesn't 
> take BKL elsewhere" does _not_ mean that we don't have races.  
> IOW, the same review ought to look for such beasts and deal with 
> them.  Mere "oh, no BKL anywhere in that fs" is not enough to 
> discard the ->remount_fs() instance.

what kind of races do you mean? Timing sensitive ones that are there 
just are not easy to trigger with the BKL held?

Or actual locking interaction between that body of BKL code and all 
other BKL using code?

	Ingo
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