From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753447AbbCBIfu (ORCPT <rfc822;w@1wt.eu>);
	Mon, 2 Mar 2015 03:35:50 -0500
Received: from bombadil.infradead.org ([198.137.202.9]:55380 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751117AbbCBIfr (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 2 Mar 2015 03:35:47 -0500
Date: Mon, 2 Mar 2015 09:35:30 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Kosina <jkosina@suse.cz>
Cc: mingo@kernel.org, rusty@rustcorp.com.au, mathieu.desnoyers@efficios.com,
        oleg@redhat.com, paulmck@linux.vnet.ibm.com,
        linux-kernel@vger.kernel.org, andi@firstfloor.org, rostedt@goodmis.org,
        tglx@linutronix.de, Seth Jennings <sjenning@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.cz>
Subject: Re: [RFC][PATCH 1/9] klp: Fix obvious RCU fail
Message-ID: <20150302083530.GD5029@twins.programming.kicks-ass.net>
References: <20150228212447.381543289@infradead.org>
 <20150228213109.893891745@infradead.org>
 <alpine.LNX.2.00.1503012108270.9089@pobox.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.LNX.2.00.1503012108270.9089@pobox.suse.cz>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sun, Mar 01, 2015 at 09:09:24PM +0100, Jiri Kosina wrote:
> On Sat, 28 Feb 2015, Peter Zijlstra wrote:
> 
> > While one must hold RCU-sched (aka. preempt_disable) for find_symbol()
> > one must equally hold it over the use of the object returned.
> > 
> > The moment you release the RCU-sched read lock, the object can be dead
> > and gone.
> > 
> > Cc: Seth Jennings <sjenning@redhat.com>
> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> > Cc: Miroslav Benes <mbenes@suse.cz>
> > Cc: Petr Mladek <pmladek@suse.cz>
> > Cc: Jiri Kosina <jkosina@suse.cz>
> > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > Cc: Rusty Russell <rusty@rustcorp.com.au>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> 
> Acked-by: Jiri Kosina <jkosina@suse.cz>
> 
> I guess you'll be taking this together with the series, so I am not 
> applying it.

Feel free to take it; this series might take a wee while longer to
mature.

That said; I do have a follow up question on that code. So now you've
successfully obtained an address in module space; but the moment you
release that RCU-sched lock, the module can be gone.

How does the whole live patching stuff deal with module removal during
patching?