From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 1842C6B0275 for ; Thu, 4 Oct 2018 03:49:38 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id m45-v6so4727098edc.2 for ; Thu, 04 Oct 2018 00:49:38 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d33-v6si1394157edd.393.2018.10.04.00.49.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 04 Oct 2018 00:49:36 -0700 (PDT) Date: Thu, 4 Oct 2018 09:49:33 +0200 From: Petr Mladek Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes" Message-ID: <20181004074933.5pzqnjzl4pwuutoj@pathway.suse.cz> References: <20180927194601.207765-1-wonderfly@google.com> <20181001152324.72a20bea@gandalf.local.home> <20181002084225.6z2b74qem3mywukx@pathway.suse.cz> <20181002212327.7aab0b79@vmware.local.home> <20181003091400.rgdjpjeaoinnrysx@pathway.suse.cz> <20181003133704.43a58cf5@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181003133704.43a58cf5@gandalf.local.home> Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt Cc: Daniel Wang , 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 Wed 2018-10-03 13:37:04, Steven Rostedt wrote: > On Wed, 3 Oct 2018 10:16:08 -0700 > Daniel Wang wrote: > > > On Wed, Oct 3, 2018 at 2:14 AM Petr Mladek wrote: > > > > > > On Tue 2018-10-02 21:23:27, Steven Rostedt wrote: > > > > 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") > > > > > > As I said, I am fine with backporting the console_lock owner stuff > > > into the stable release. > > > > > > I just wonder (like Sergey) what the real problem is. The console_lock > > > owner handshake is not fully reliable. It is might be good enough > > I'm not sure what you mean by 'not fully reliable' I mean that it is not guaranteed that the very first printk() takes over the console. It will happen only when the other printk() calls console_trylock_spinning() while the current console owner does the code between: console_lock_spinning_enable(); console_lock_spinning_disable_and_check(); > > > Just to be sure. Daniel, could you please send a log with > > > the console_lock owner stuff backported? There we would see > > > who called the panic() and why it rebooted early. > > > > Sure. Here is one. It's a bit long but complete. I attached another log > > snippet below it which is what I got when `softlockup_panic` was turned > > off. The log was from the IRQ task that was flushing the printk buffer. I > > will be taking a closer look at it too but in case you'll find it helpful. > > Just so I understand correctly. Does the panic hit with and without the > suggested backport patch? The only difference is that you get the full > output with the patch and limited output without it? Sigh, the other mail suggest that there was a real deadlock. It means that the console owner logic might help but it would not prevent the deadlock completely. Best Regards, Petr