From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by kanga.kvack.org (Postfix) with ESMTP id E07A96B0005 for ; Tue, 2 Oct 2018 21:23:33 -0400 (EDT) Received: by mail-pl1-f197.google.com with SMTP id m3-v6so4337894plt.9 for ; Tue, 02 Oct 2018 18:23:33 -0700 (PDT) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id q10-v6si17226108pgk.392.2018.10.02.18.23.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Oct 2018 18:23:32 -0700 (PDT) Date: Tue, 2 Oct 2018 21:23:27 -0400 From: Steven Rostedt Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes" Message-ID: <20181002212327.7aab0b79@vmware.local.home> In-Reply-To: References: <20180927194601.207765-1-wonderfly@google.com> <20181001152324.72a20bea@gandalf.local.home> <20181002084225.6z2b74qem3mywukx@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Wang Cc: Petr Mladek , stable@vger.kernel.org, Alexander.Levin@microsoft.com, akpm@linux-foundation.org, byungchul.park@lge.com, dave.hansen@intel.com, hannes@cmpxchg.org, jack@suse.cz, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mathieu Desnoyers , Mel Gorman , mhocko@kernel.org, pavel@ucw.cz, penguin-kernel@i-love.sakura.ne.jp, peterz@infradead.org, tj@kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz, Cong Wang , Peter Feiner On Tue, 2 Oct 2018 17:15:17 -0700 Daniel Wang wrote: > On Tue, Oct 2, 2018 at 1:42 AM Petr Mladek wrote: > > > > Well, I still wonder why it helped and why you do not see it with 4.4. > > I have a feeling that the console owner switch helped only by chance. > > In fact, you might be affected by a race in > > printk_safe_flush_on_panic() that was fixed by the commit: > > > > 554755be08fba31c7 printk: drop in_nmi check from printk_safe_flush_on_panic() > > > > The above one commit might be enough. Well, there was one more > > NMI-related race that was fixed by: > > > > ba552399954dde1b printk: Split the code for storing a message into the log buffer > > a338f84dc196f44b printk: Create helper function to queue deferred console handling > > 03fc7f9c99c1e7ae printk/nmi: Prevent deadlock when accessing the main log buffer in NMI > > All of these commits already exist in 4.14 stable, since 4.14.68. The deadlock > still exists even when built from 4.14.73 (latest tag) though. And cherrypicking > dbdda842fe96 fixes it. > I don't see the big deal of backporting this. The biggest complaints about backports are from fixes that were added to late -rc releases where the fixes didn't get much testing. This commit was added in 4.16, and hasn't had any issues due to the design. Although a fix has been added: c14376de3a1 ("printk: Wake klogd when passing console_lock owner") Also from 4.16, but nothing else according to searching for "Fixes" tags. -- Steve