Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753058AbbBMOTV (ORCPT ); Fri, 13 Feb 2015 09:19:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44101 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752620AbbBMOTU (ORCPT ); Fri, 13 Feb 2015 09:19:20 -0500 Date: Fri, 13 Feb 2015 08:19:04 -0600 From: Josh Poimboeuf To: Jiri Kosina Cc: Seth Jennings , Vojtech Pavlik , Masami Hiramatsu , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/9] livepatch: consistency model Message-ID: <20150213141904.GB27180@treble.redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1542 Lines: 34 On Fri, Feb 13, 2015 at 11:14:01AM +0100, Jiri Kosina wrote: > On Mon, 9 Feb 2015, Josh Poimboeuf wrote: > > > My biggest concerns and questions related to this patch set are: > > > > 1) To safely examine the task stacks, the transition code locks each task's rq > > struct, which requires using the scheduler's internal rq locking functions. > > It seems to work well, but I'm not sure if there's a cleaner way to safely > > do stack checking without stop_machine(). > > How about we take a slightly different aproach -- put a probe (or ftrace) > on __switch_to() during a klp transition period, and examine stacktraces > for tasks that are just about to start running from there? > > The only tasks that would not be covered by this would be purely CPU-bound > tasks that never schedule. But we are likely in trouble with those anyway, > because odds are that non-rescheduling CPU-bound tasks are also > RT-priority tasks running on isolated CPUs, which we will fail to handle > anyway. > > I think Masami used similar trick in his kpatch-without-stopmachine > aproach. Yeah, that's definitely an option, though I'm really not too crazy about it. Hooking into the scheduler is kind of scary and disruptive. We'd also have to wake up all the sleeping processes. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/