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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 3E4FFC433E0 for ; Thu, 7 Jan 2021 12:49:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D75123382 for ; Thu, 7 Jan 2021 12:49:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726780AbhAGMtQ (ORCPT ); Thu, 7 Jan 2021 07:49:16 -0500 Received: from mx2.suse.de ([195.135.220.15]:57650 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728180AbhAGMtQ (ORCPT ); Thu, 7 Jan 2021 07:49:16 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1610023708; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=M3fsgJ4y1qrIo5WUjYDZW5qHVTbkdAXEHQARuQrTSQA=; b=l12sFVAYH+BxrN7h9cAZo1z18t+ytiRNq8XfT1CuTlVXqSX39LNptAduSG/4POUTvSWBUR ybQxpwK4KmW3/8V/qu3dmgAchq/w5TY2kfDWOk2ESOJxqkQrQgMN2vJbbbOR1/1i4XaDMl oHsTa71UqqoZ753ZAIIy9TiQzI/3E6M= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2D231ACAF; Thu, 7 Jan 2021 12:48:28 +0000 (UTC) Date: Thu, 7 Jan 2021 13:48:27 +0100 From: Petr Mladek To: Vineet Gupta Cc: Sergey Senozhatsky , Steven Rostedt , John Ogness , Linus Torvalds , Guenter Roeck , Shreyas Joshi , shreyasjoshi15@gmail.com, Greg Kroah-Hartman , Sergey Senozhatsky , linux-kernel@vger.kernel.org, buildroot@busybox.net, Thomas Petazzoni , linux-arch@vger.kernel.org, arcml Subject: Re: ARC no console output (was Re: [PATCH 1/2] init/console: Use ttynull as a fallback when there is no console) Message-ID: References: <20201111135450.11214-1-pmladek@suse.com> <20201111135450.11214-2-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Wed 2021-01-06 15:36:36, Vineet Gupta wrote: > +CC Buildroot folks > > Hi Petr, > > On 11/11/20 5:54 AM, Petr Mladek wrote: > > stdin, stdout, and stderr standard I/O stream are created for the init > > process. They are not available when there is no console registered > > for /dev/console. It might lead to a crash when the init process > > tries to use them, see the commit 48021f98130880dd742 ("printk: handle > > blank console arguments passed in."). > > > > Normally, ttySX and ttyX consoles are used as a fallback when no consoles > > are defined via the command line, device tree, or SPCR. But there > > will be no console registered when an invalid console name is configured > > or when the configured consoles do not exist on the system. > > > > Users even try to avoid the console intentionally, for example, > > by using console="" or console=null. It is used on production > > systems where the serial port or terminal are not visible to > > users. Pushing messages to these consoles would just unnecessary > > slowdown the system. > > > > Make sure that stdin, stdout, stderr, and /dev/console are always > > available by a fallback to the existing ttynull driver. It has > > been implemented for exactly this purpose but it was used only > > when explicitly configured. > > > > Signed-off-by: Petr Mladek > > > --- a/init/main.c > > +++ b/init/main.c > > @@ -1470,8 +1470,14 @@ void __init console_on_rootfs(void) > > struct file *file = filp_open("/dev/console", O_RDWR, 0); > > if (IS_ERR(file)) { > > - pr_err("Warning: unable to open an initial console.\n"); > > - return; > > + pr_err("Warning: unable to open an initial console. Fallback to ttynull.\n"); > > + register_ttynull_console(); > > + > > + file = filp_open("/dev/console", O_RDWR, 0); > > + if (IS_ERR(file)) { > > + pr_err("Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process!\n"); > > + return; > > + } > > > This breaks ARC booting (no output on console). This is likely the same problem as with kunit and um kernels. It is being discussed at https://lore.kernel.org/linux-kselftest/X%2FSRA1P8t+ONZFKb@alley/#t We have several workarounds. I am still squashing my head about the right solution. The console registration code is like a vasps' nest. It is always a pain when we touch it. I hope that I will send a patchset for review later today. In the worst case, we will revert the patch in the mainline. > Our Buildroot based setup has dynamic /dev where /dev/console doesn't exist > statically and there's a primoridla /init shell script which does following > > /bin/mount -t devtmpfs devtmpfs /dev > exec 0 exec 1>/dev/console > exec 2>/dev/console > exec /sbin/init "$@" > > Buildroot has had this way of handling missing /dev/console since 2011 [1] > and [2]. Good to know. > Please advise what needs to be done to unbork boot. Otherwise this seems > like a kernel change which breaks user-space and needs to be backed-out (or > perhaps conditionalize on CONFIG_NULL_TTY. I'm surprised it hasn't been > reported by any other embedded folks Two workarounds can be fount at https://lore.kernel.org/linux-kselftest/X%2FSYhBZyudfnKY1u@alley/ https://lore.kernel.org/linux-kselftest/X%2FW2sl7RMvfaV4Ru@alley/ But I still see them as only a partial solutiuon. I still another sources of potential problems. Best Regards, Petr