From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41416C07E85 for ; Tue, 11 Dec 2018 08:22:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 10FF22082F for ; Tue, 11 Dec 2018 08:22:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10FF22082F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726215AbeLKIWZ (ORCPT ); Tue, 11 Dec 2018 03:22:25 -0500 Received: from mx2.suse.de ([195.135.220.15]:56728 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726069AbeLKIWY (ORCPT ); Tue, 11 Dec 2018 03:22:24 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 722BBAEBD; Tue, 11 Dec 2018 08:22:22 +0000 (UTC) Date: Tue, 11 Dec 2018 09:22:21 +0100 From: Petr Mladek To: Sergey Senozhatsky Cc: Feng Tang , Peter Zijlstra , akpm@linux-foundation.org, bp@suse.de, keescook@chromium.org, mm-commits@vger.kernel.org, sergey.senozhatsky@gmail.com, stable@vger.kernel.org, tglx@linutronix.de, Steven Rostedt , Sasha Levin , Andi Kleen , linux-kernel@vger.kernel.org Subject: Re: + panic-avoid-the-extra-noise-dmesg.patch added to -mm tree Message-ID: <20181211082221.3wovowe6tql5o3s4@pathway.suse.cz> References: <20181205024713.nqyt6qiamokq7qtl@shbuild888> <20181205025728.GC503@jagdpanzerIV> <20181205052912.GA423@jagdpanzerIV> <20181205080044.GA11190@jagdpanzerIV> <20181205154620.4dqtledc2duhrp2c@shbuild888> <20181206035825.jz2bfh3errj23rjq@shbuild888> <20181207095004.GB3729@jagdpanzerIV> <20181210094554.z5n7dmkrnlcpygg4@shbuild888> <20181210155705.qowbi7xvszzfonzk@pathway.suse.cz> <20181211080743.GB521@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181211080743.GB521@jagdpanzerIV> User-Agent: NeoMutt/20170421 (1.8.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 2018-12-11 17:07:43, Sergey Senozhatsky wrote: > On (12/10/18 16:57), Petr Mladek wrote: > > > > (masked out) and on panic_cpu disables only SDEI (interrupts from firmware, > > > > if I got it right); so it seems that arm64 can handle IRQs after panic. And > > > > if there are platforms that handle IRQ (including sysrq) after panic, then > > > > both options - making printk a noop or keeping local irqs off - maybe can > > > > cause some problems. Or maybe not. We better ask arch people. > > > > > > Yes, this is very valid concern. And after Petr and you raised it, I did > > > some experiments with 3 x86 platforms at my hand, one Apollolake IOT device > > > with serial console, one IvyBridge laptop and one Kabylake NUC, the magic key > > > all works well before panic, and fails after panic. But I did remember the > > > PageUp/PageDown key worked on some laptop years ago. And you actually raised a > > > good question: what do we expect for the post-panic kernel? > > > > I am not sure why it does not work. But it would be nice if sysrq > > worked. > > Absolutely. > > [..] > > I still think that calming down printk() is acceptable when > > it can be restored from sysrq. > > I would agree; peeking one of the two solutions, printk patch is > probably preferable. > > > I think that only few people might be interested into debugging > > post-panic problems. We could print a warning for them about > > that printk() has got disabled. > > Dunno. This _maybe_ (speculation!) can upset folks on those platforms > that have sysrq working after panic. printk is a common code. > > I'm probably missing a lot of things here, but just in case, I'm not > sure at which point the idea of patching some files under arch/x86 > directory was ruled out and why. I suggested to clear the panic_blinking (or whatever name) in __handle_sysrq(). The idea is that sysrq needs manual intervention. It allows to see the original message before it gets overridden by a potential sysrq-related output. It assumes that sysrq is the only interesting operation when printk() might be useful at this state. Best Regards, Petr