From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage Date: Mon, 22 Nov 2010 00:39:49 +0900 Message-ID: <20101121153949.GD20947@barrios-desktop> References: <20101121112611.GB4267@deepthought.bhanu.net> <20101121133024.GF23423@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Ted Ts'o , linux-ext4@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Dilger , Paul McKenney Received: from mail-pz0-f46.google.com ([209.85.210.46]:48106 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754031Ab0KUPj5 (ORCPT ); Sun, 21 Nov 2010 10:39:57 -0500 Content-Disposition: inline In-Reply-To: <20101121133024.GF23423@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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