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Date: Mon, 22 Nov 2010 00:39:49 +0900
From: Minchan Kim <minchan.kim@gmail.com>
To: "Ted Ts'o" <tytso@mit.edu>, linux-ext4@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Eric Sandeen <sandeen@redhat.com>
Subject: Re: [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage
Message-ID: <20101121153949.GD20947@barrios-desktop>
References: <20101121112611.GB4267@deepthought.bhanu.net>
 <20101121133024.GF23423@thunk.org>
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On Sun, Nov 21, 2010 at 08:30:24AM -0500, Ted Ts'o wrote:
> On Sun, Nov 21, 2010 at 07:26:11PM +0800, Arun Bhanu wrote:
> > I saw this in kernel log messages while testing 2.6.37-rc2. I think it
> > appeared while mounting an external hard-disk. I can't seem to
> > reproduce it.
> 
> I could be wrong but this looks like it's a bug in mm/migrate.c in
> migrate_page_move_mapping(): it is calling radix_tree_lookup_slot()
> without first taking an rcu_read_lock().
> 
> It was triggered by a memory allocation out of ext4_fill_super(),
> which then triggered a memory compaction/migration, but I don't
> believe it's otherwise related to the ext4 code.
> 
> Over to the linux-mm folks for confirmation...

I think it's no problem. 

That's because migration always holds lock_page on the file page.
So the page couldn't remove from radix. 


-- 
Kind regards,
Minchan Kim
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