linux-kernel - Re: hugetlb locking bug.

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Date:	Wed, 14 Dec 2011 06:59:13 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	William Irwin <wli@...omorphy.com>,
	Ingo Molnar <mingo@...hat.com>,
	Tyler Hicks <tyhicks@...onical.com>
Subject: Re: hugetlb locking bug.

On Fri, 2011-04-15 at 14:27 -0700, Linus Torvalds wrote:
> On Fri, Apr 15, 2011 at 2:19 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > (Warning: whitespace damage and TOTALLY UNTESTED)
> 
> Gaah. That won't work. Or rather, it probably may work, but while
> working it will spam the logs with that
> 
>     WARN_ON(!(inode->i_state & I_NEW));
> 
> thing from unlock_new_inode.
> 
> So the sane thing to do would be apparently one of
> 
>  (a) ignore the whole thing, and just accept the false lockdep warning.
> 
>       which I'd be willing to do, but it might be hiding some real
> ones, so we probably shouldn't.
> 
>  (b) just remove that WARN_ON(), and use the one-liner I suggested
> 
>  (c) extract the "set directory i_mutex key" logic into a new helper
> function for the case of filesystems like hugetlbfs that don't want to
> use unlock_new_inode() for one reason or another.
> 
> Personally, I don't have any really strong preferences and would
> probably just go for (b) to keep the patch small and simple. Anybody?
> 
>                      Linus

Since this discussion, commit "e096d0c lockdep: Add helper function for
dir vs file i_mutex annotation" defined a helper function
lockdep_annotate_inode_mutex_key(), but only hugetlbfs calls it.  There
are plenty of other places where new_inode() is called without
unlock_new_inode() (eg. proc, devpts, debugfs, ramfs, ...).  Is this
omission intentional or should they be annotated?  

An incomplete patch was posted
http://marc.info/?l=linux-fsdevel&m=132369346810326&w=2

(Tyler Hicks' "vfs: Correctly set the dir i_mutex lockdep class" patch
http://marc.info/?l=linux-fsdevel&m=132370587315054&w=2 should be
prereq'ed.)

thanks,

Mimi

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