linux-kernel - Re: hugetlbfs lockdep spew revisited.

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Message-ID: <20120217003415.GM23916@ZenIV.linux.org.uk>
Date:	Fri, 17 Feb 2012 00:34:15 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	tyhicks@...onical.com
Subject: Re: hugetlbfs lockdep spew revisited.

On Thu, Feb 16, 2012 at 07:16:34PM -0500, Josh Boyer wrote:
> On Thu, Feb 16, 2012 at 07:08:57PM -0500, Dave Jones wrote:
> > Remember this ? https://lkml.org/lkml/2011/4/15/272
> > Josh took a stab at fixing it in e096d0c7e2e4e5893792db865dd065ac73cf1f00,
> > but it seems to still be there.
> 
> I think Tyler Hicks actually noticed this a while ago, but his patch has
> been waiting on comment from Al and Christoph:
> 
> http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565
> 
> I've been hesitant to comment because I obviously screwed up once
> already.  We could try this patch in Fedora for a while if Al and
> company don't speak up soon.

That has nothing to do with the deadlock in question; it's *NOT* about
directories at all and no, it's not a false positive.

This is very simple: ->mmap() should never take ->i_mutex.  Directories
have nothing to do with that.  Simple grep for i_mutex in fs/hugetlbfs/*.c
will instantly show its use for non-directories, with pagefaults taken
while holding it.  Pagefault handlers take ->mmap_sem; so does ->mmap()
caller.  QED.
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