From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f199.google.com (mail-qt0-f199.google.com [209.85.216.199]) by kanga.kvack.org (Postfix) with ESMTP id 76CB66B0033 for ; Wed, 17 Jan 2018 15:06:01 -0500 (EST) Received: by mail-qt0-f199.google.com with SMTP id h32so10822170qtb.9 for ; Wed, 17 Jan 2018 12:06:01 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id t186sor3540609qkf.156.2018.01.17.12.06.00 for (Google Transport Security); Wed, 17 Jan 2018 12:06:00 -0800 (PST) Date: Wed, 17 Jan 2018 12:05:51 -0800 From: Tejun Heo Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Message-ID: <20180117200551.GW3460072@devbig577.frc2.facebook.com> References: <20180111045817.GA494@jagdpanzerIV> <20180111093435.GA24497@linux.suse> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180117121251.7283a56e@gandalf.local.home> Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt 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@home.goodmis.org, Byungchul Park , Pavel Machek , linux-kernel@vger.kernel.org Hello, Steven. On Wed, Jan 17, 2018 at 12:12:51PM -0500, Steven Rostedt wrote: > From what I gathered, you said an OOM would trigger, and then the > network console would not be able to allocate memory and it would > trigger a printk too, and cause an infinite amount of printks. Yeah, it falls into back-and-forth loop between the OOM code and netconsole path. > This could very well be a great place to force offloading. If a printk > is called from within a printk, at the same context (normal, softirq, > irq or NMI), then we should trigger the offloading. I was thinking more of a timeout based approach (ie. if stuck for longer than X or X messages, offload), but if local feedback loop is the only thing we're missing after your improvements, detecting that specific condition definitely works and is likely a better approach in terms of message delivery guarantee. > +static void kick_offload_thread(void) > +{ > + /* > + * Consoles are triggering printks, offload the printks > + * to another CPU to hopefully avoid a lockup. > + */ > +} ... > @@ -2333,6 +2390,7 @@ void console_unlock(void) > > for (;;) { > struct printk_log *msg; > + bool offload; > size_t ext_len = 0; > size_t len; > > @@ -2393,15 +2451,20 @@ void console_unlock(void) > * waiter waiting to take over. > */ > console_lock_spinning_enable(); > + offload = recursion_check_start(); > > stop_critical_timings(); /* don't trace print latency */ > call_console_drivers(ext_text, ext_len, text, len); > start_critical_timings(); > > + recursion_check_finish(offload); > + > if (console_lock_spinning_disable_and_check()) { > printk_safe_exit_irqrestore(flags); > return; > } > + if (offload) > + kick_offload_thread(); Yeah, something like this would definitely work. Thanks a lot. -- tejun -- 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