From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755783AbeATOvp (ORCPT ); Sat, 20 Jan 2018 09:51:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:57488 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754301AbeATOvg (ORCPT ); Sat, 20 Jan 2018 09:51:36 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB1F1214E1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Sat, 20 Jan 2018 09:51:31 -0500 From: Steven Rostedt To: Tejun Heo Cc: Petr Mladek , Sergey Senozhatsky , Sergey Senozhatsky , akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang , Dave Hansen , Johannes Weiner , Mel Gorman , Michal Hocko , Vlastimil Babka , Peter Zijlstra , Linus Torvalds , Jan Kara , Mathieu Desnoyers , Tetsuo Handa , rostedt@rostedt.homelinux.com, Byungchul Park , Pavel Machek , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Message-ID: <20180120095131.57601321@gandalf.local.home> In-Reply-To: <20180120121953.GA1096857@devbig577.frc2.facebook.com> References: <20180111103845.GB477@jagdpanzerIV> <20180111112908.50de440a@vmware.local.home> <20180111203057.5b1a8f8f@gandalf.local.home> <20180111215547.2f66a23a@gandalf.local.home> <20180116194456.GS3460072@devbig577.frc2.facebook.com> <20180117091208.ezvuhumnsarz5thh@pathway.suse.cz> <20180117151509.GT3460072@devbig577.frc2.facebook.com> <20180117121251.7283a56e@gandalf.local.home> <20180117134201.0a9cbbbf@gandalf.local.home> <20180119132052.02b89626@gandalf.local.home> <20180120121953.GA1096857@devbig577.frc2.facebook.com> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 20 Jan 2018 04:19:53 -0800 Tejun Heo wrote: > I'm a bit worried tho because this essentially seems like "detect > recursion, ignore messages" approach. netcons can have a very large > surface for bugs. Suppressing those messages would make them > difficult to debug. For example, all our machines have both serial > console (thus the slowness) and netconsole hooked up and netcons code > has had its fair share of issues. This would likely make tracking > down those problems more challenging. Well, it's not totally ignoring them. There's a variable that tells printk how many to print before it starts ignoring them. I picked 3, but that could very well be 5 or 10. Probably 10 is the best, because then it would give us enough idea why printk is recursing on itself without overloading the buffer. And I made it a variable to easily make it a knob for userspace to tweak if need be. > > Can we discuss pros and cons of this approach against offloading > before committing to this? I'm open. I was just thinking about the scenario that you mentioned and how what the best way to solve it would be. We need to define the exact problem(s) we are dealing with before we offer a solution. The one thing I don't want is a solution looking for a problem. I want a full understanding of what the problem exactly is and then we can discuss various solutions, and how they solve the problem(s). Otherwise we are just doing (to quote Linus) code masturbation. -- Steve