From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932280AbeAKLvF (ORCPT + 1 other); Thu, 11 Jan 2018 06:51:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:41105 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751639AbeAKLvE (ORCPT ); Thu, 11 Jan 2018 06:51:04 -0500 Date: Thu, 11 Jan 2018 12:50:59 +0100 From: Petr Mladek To: Sergey Senozhatsky Cc: Steven Rostedt , Tejun Heo , 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@home.goodmis.org, Byungchul Park , Pavel Machek , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Message-ID: <20180111115059.GA24419@linux.suse> References: <20180110132418.7080-1-pmladek@suse.com> <20180110140547.GZ3668920@devbig577.frc2.facebook.com> <20180110130517.6ff91716@vmware.local.home> <20180111045817.GA494@jagdpanzerIV> <20180111093435.GA24497@linux.suse> <20180111103845.GB477@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180111103845.GB477@jagdpanzerIV> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Thu 2018-01-11 19:38:45, Sergey Senozhatsky wrote: > On (01/11/18 10:34), Petr Mladek wrote: > [..] > > > except that handing off a console_sem to atomic task when there > > > is O(logbuf) > watchdog_thresh is a regression, basically... > > > it is what it is. > > > > How this could be a regression? Is not the victim that handles > > other printk's random? What protected the atomic task to > > handle the other printks before this patch? > > the non-atomic -> atomic context console_sem transfer. we previously > would have kept the console_sem owner to its non-atomic owner. we now > will make sure that if printk from atomic context happens then it will > make it to console_unlock() loop. > emphasis on O(logbuf) > watchdog_thresh. Sergey, please, why do you completely and repeatedly ignore that argument about statistical effects? Yes, the above scenario is possible. But Steven's patch might also move the owner from atomic context to a non-atomic one. The chances should be more or less equal. The main advantage is that the owner is moved. This should statistically lower the chance of a soft-lockup. > > > Or do you have a system that started to suffer from softlockups > > with this patchset and did not do this before? > [..] > > Do you know about any system where this patch made the softlockup > > deterministically or statistically more likely, please? > > I have explained many, many times why my boards die just like before. > why would I bother collecting any numbers... Is it with your own printk stress tests or during "normal" work? If it is during a normal work, is there any chance that we could have a look at the logs? Best Regards, Petr From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 26A2A6B026B for ; Thu, 11 Jan 2018 06:51:06 -0500 (EST) Received: by mail-wm0-f70.google.com with SMTP id z83so1309841wmc.5 for ; Thu, 11 Jan 2018 03:51:06 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p9si2669516wra.111.2018.01.11.03.51.04 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 11 Jan 2018 03:51:04 -0800 (PST) Date: Thu, 11 Jan 2018 12:50:59 +0100 From: Petr Mladek Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Message-ID: <20180111115059.GA24419@linux.suse> References: <20180110132418.7080-1-pmladek@suse.com> <20180110140547.GZ3668920@devbig577.frc2.facebook.com> <20180110130517.6ff91716@vmware.local.home> <20180111045817.GA494@jagdpanzerIV> <20180111093435.GA24497@linux.suse> <20180111103845.GB477@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180111103845.GB477@jagdpanzerIV> Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Steven Rostedt , Tejun Heo , 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@home.goodmis.org, Byungchul Park , Pavel Machek , linux-kernel@vger.kernel.org On Thu 2018-01-11 19:38:45, Sergey Senozhatsky wrote: > On (01/11/18 10:34), Petr Mladek wrote: > [..] > > > except that handing off a console_sem to atomic task when there > > > is O(logbuf) > watchdog_thresh is a regression, basically... > > > it is what it is. > > > > How this could be a regression? Is not the victim that handles > > other printk's random? What protected the atomic task to > > handle the other printks before this patch? > > the non-atomic -> atomic context console_sem transfer. we previously > would have kept the console_sem owner to its non-atomic owner. we now > will make sure that if printk from atomic context happens then it will > make it to console_unlock() loop. > emphasis on O(logbuf) > watchdog_thresh. Sergey, please, why do you completely and repeatedly ignore that argument about statistical effects? Yes, the above scenario is possible. But Steven's patch might also move the owner from atomic context to a non-atomic one. The chances should be more or less equal. The main advantage is that the owner is moved. This should statistically lower the chance of a soft-lockup. > > > Or do you have a system that started to suffer from softlockups > > with this patchset and did not do this before? > [..] > > Do you know about any system where this patch made the softlockup > > deterministically or statistically more likely, please? > > I have explained many, many times why my boards die just like before. > why would I bother collecting any numbers... Is it with your own printk stress tests or during "normal" work? If it is during a normal work, is there any chance that we could have a look at the logs? Best Regards, Petr -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org