linux-kernel - Re: [RFC PATCH 0/2] Fix up the NFS mmap code

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Date:	Fri, 8 Jan 2010 18:22:01 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...IV.linux.org.uk>
cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-nfs@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Fix up the NFS mmap code

On Sat, 9 Jan 2010, Al Viro wrote:
> 
> Well, sure - it steps on i_mutex-before-mmmap_sem first from ls somewhere and
> records the ordering for posterity.  Then NFS steps into mmap() (on a
> different inode) and gets conflicting ordering.

Look closer: the inodes for directories and for non-directories have 
i_mutex in different lockdep classes.

So that "on a different inode" thing should have made it a non-issue, 
since there is no actual chain back. There is "mmap_sem -> 
i_mutex_regular_file" (for mmap) and there is "i_mutex_directory -> 
mmap_sem" (for filldir), but that isn't an ABBA.

The problem _seems_ to be (if I read Andi's chain correctly) that a 
directory hasn't gone through the i_mutex_dir_key change, so filldir ends 
up being counted against the default i_mutex_key.

		Linus
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