From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755493AbYANDnh (ORCPT ); Sun, 13 Jan 2008 22:43:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754206AbYANDn0 (ORCPT ); Sun, 13 Jan 2008 22:43:26 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:40682 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753958AbYANDnZ (ORCPT ); Sun, 13 Jan 2008 22:43:25 -0500 Date: Mon, 14 Jan 2008 03:43:23 +0000 From: Al Viro To: Neil Brown Cc: Andrew Morton , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array. Message-ID: <20080114034322.GO27894@ZenIV.linux.org.uk> References: <20080114123726.19968.patches@notabene> <1080114014531.20354@suse.de> <20080114020459.GN27894@ZenIV.linux.org.uk> <18314.54601.196877.828373@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <18314.54601.196877.828373@notabene.brown> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 14, 2008 at 02:21:45PM +1100, Neil Brown wrote: > Maybe it isn't there any more.... > > Once upon a time, when I > echo remove > /sys/block/mdX/md/dev-YYY/state Egads. And just what will protect you from parallel callers of state_store()? buffer->mutex does *not* do that - it only gives you exclusion on given struct file. Run the command above from several shells and you've got independent open from each redirect => different struct file *and* different buffer for each => no exclusion whatsoever. And _that_ is present right in the mainline tree - it's unrelated to -mm kobject changes. BTW, yes, you do have a deadlock there - kobject_del() will try to evict children, which will include waiting for currently running ->store() to finish, which will include the caller since .../state *is* a child of that sucker. The real problem is the lack of any kind of exclusion considerations in md.c itself, AFAICS. Fun with ordering is secondary (BTW, yes, it is a problem - will sysfs ->store() to attribute between export_rdev() and kobject_del() work correctly?)