linux-kernel - Re: [RFC][PATCH 1/9] klp: Fix obvious RCU fail

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Message-ID: <20150302083530.GD5029@twins.programming.kicks-ass.net>
Date:	Mon, 2 Mar 2015 09:35:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	mingo@...nel.org, rusty@...tcorp.com.au,
	mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, rostedt@...dmis.org, tglx@...utronix.de,
	Seth Jennings <sjenning@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.cz>
Subject: Re: [RFC][PATCH 1/9] klp: Fix obvious RCU fail

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@...hat.com>
> > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> > Cc: Miroslav Benes <mbenes@...e.cz>
> > Cc: Petr Mladek <pmladek@...e.cz>
> > Cc: Jiri Kosina <jkosina@...e.cz>
> > Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> Acked-by: Jiri Kosina <jkosina@...e.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?
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