linux-kernel - Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected

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Date:	Mon, 5 Mar 2012 15:46:22 -0600
From:	Tyler Hicks <tyhicks@...onical.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dustin Kirkland <dustin.kirkland@...zang.com>,
	ecryptfs@...r.kernel.org
Subject: Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking
 dependency detected

On 2012-03-05 21:35:58, Al Viro wrote:
> On Mon, Mar 05, 2012 at 01:23:34PM -0800, Andrew Morton wrote:
> > mmap_sem nests inside i_mutex.
> > 
> > On the path
> > 
> > 	munmap
> > 	->ecryptfs_vma_close
> > 	  ->filemap_write_and_wait
> > 	    ->generic_file_aio_write
> > 
> > we're taking i_mutex inside mmap_sem.  So the problem is triggered by
> > ecryptfs_vma_close() calling filemap_write_and_wait() inside munmap()'s
> > mmap_sem.
> > 
> > Question is: what did we recently change to cause this to happen?
> 
> AFAICS, it's commit 32001d6fe9ac6b0423e674a3093aa56740849f3b
> Author: Tyler Hicks <tyhicks@...onical.com>
> Date:   Mon Nov 21 17:31:29 2011 -0600
> 
>     eCryptfs: Flush file in vma close

Yes, it is definitely this commit. This is mainly what brought about my
patch to fix the incorrect logic around lockdep_set_class() in
lockdep_annotate_inode_mutex_key(). With that patch, I no longer saw
these lockdep warnings, so I wrote it off. Al has since made it clear
that this locking order is wrong.

This should fix itself when I revert
57db4e8d73ef2b5e94a3f412108dff2576670a8a. We'll no longer need this
flush in vma_close(), so 32001d6fe9ac6b0423e674a3093aa56740849f3b will
be reverted, too. I was planning on waiting until 3.4 to do all of that
since it will be a somewhat big change (even though it is mainly
reverting of patches).

Tyler

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