linux-kernel - Re: [BUG?] [Ext4] INFO: suspicious rcu_dereference

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Message-ID: <20101121173726.GG23423@thunk.org>
Date:	Sun, 21 Nov 2010 12:37:26 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	linux-ext4@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Eric Sandeen <sandeen@...hat.com>
Subject: Re: [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage

On Mon, Nov 22, 2010 at 12:39:49AM +0900, Minchan Kim wrote:
> 
> 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. 

It may be "ok" in that it won't cause a race, but it still leaves an
unsightly warning if LOCKDEP is enabled, and LOCKDEP warnings will
cause /proc_lock_stat to be disabled.  So I think it still needs to be
fixed by adding rcu_read_lock()/rcu_read_unlock() to
migrate_page_move_mapping().

      	 					     - Ted
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