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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 5F8C5C43387 for ; Fri, 11 Jan 2019 13:07:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2EEB32133F for ; Fri, 11 Jan 2019 13:07:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="QDNfNczV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732581AbfAKNHh (ORCPT ); Fri, 11 Jan 2019 08:07:37 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:42262 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732564AbfAKNHf (ORCPT ); Fri, 11 Jan 2019 08:07:35 -0500 Received: by mail-pl1-f194.google.com with SMTP id y1so6745893plp.9 for ; Fri, 11 Jan 2019 05:07:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=kBdmbqrqZGCDFNNdFNSivV8+bHiJ8p/Kjme4d3AE51w=; b=QDNfNczVk8q5SIWTbzrDnpMWmL5Z+HHZCd1PQK7GrG/KjZx+dLPeLbp7Fcc5BVQND7 KihRnmWDeK3+AI9EbZGlalqxd/bUj+Qssg5A2fhtIKOPZh/l0kdhuiWjJscnHCg5QlCs OhJkxD+bP1gfFXdZUER0hpEzQjWOrJZljdUvzs90T92TGv3Io5ofwz7vfToBF6IeqMdH g5xNOeBkii5CQa97KnqKqocX/DYeFrNbngROAEgWa3Ivry2jZ6uZ3niLwo4+G1zkAeK5 DP0E0cEnMeWZm3cPTIxCYsGQhxEDWm6mAHXyHmCxkVf8vip7EdrDqme2JcPcc4/KJMh+ Q26w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=kBdmbqrqZGCDFNNdFNSivV8+bHiJ8p/Kjme4d3AE51w=; b=pE2cawlNDNyfvnSrHzMIwCO2nSiTDXwZfk6swEP3Chz+D+DeSQMW/Cf4My6RJtNJgt 3JV9AWiXVWMI4nhXspif4LIaKhZPJToCGM0ePpSYdcF27PdZ2XmI5eTPplVZtTZhV6vp IsjDWrKA+j0zxfSv7qvPQsGbe4vnALz+vvb7aqpOEyxaEIfVCozRDerkIXtYxy/hw7xu L8f2gq7vZDnl7ZCeab5P0vagwxlu0dHCSfrgMJQcbHOD8FYbQUIGAZeoQfEOxcxEsPtU mQfBNxBBTP/wXUkCyvugwtSglSSn9lUIVYXXeiOqXSv10qIXHeWE0TbqAMed1LJ8bekm s49g== X-Gm-Message-State: AJcUukdSwTrMDDM0PsGcyCyHw91YooNVCPHkshc8B1ksIA10WjCEk2C3 jNPQH0kOh8J5k4N/rj3jxKo= X-Google-Smtp-Source: ALg8bN5nIdAujCqD6Q9CH34G9NkY5X1rFHt5JvVdJmodZF9BQCxU8/KlOHK024eqWh+65qtdIEXyuQ== X-Received: by 2002:a17:902:925:: with SMTP id 34mr14085011plm.14.1547212053377; Fri, 11 Jan 2019 05:07:33 -0800 (PST) Received: from localhost ([121.137.63.184]) by smtp.gmail.com with ESMTPSA id l11sm104458445pff.65.2019.01.11.05.07.31 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 11 Jan 2019 05:07:32 -0800 (PST) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Fri, 11 Jan 2019 22:07:29 +0900 To: Petr Mladek Cc: Greg Kroah-Hartman , Jiri Slaby , Sergey Senozhatsky , Steven Rostedt , Sergey Senozhatsky , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sysrq: Restore original console_loglevel when sysrq disabled Message-ID: <20190111130729.GA31790@tigerII.localdomain> References: <20190111124515.11017-1-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190111124515.11017-1-pmladek@suse.com> User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (01/11/19 13:45), Petr Mladek wrote: > The sysrq header line is printed with an increased loglevel > to provide users some positive feedback. > > The original loglevel is not restored when the sysrq operation > is disabled. This bug was introduced in 2.6.12 (pre-git-history) > by the commit ("Allow admin to enable only some of the Magic-Sysrq > functions"). Good find, and the patch looks OK to me. A small comment below. FWIW, Reviewed-by: Sergey Senozhatsky --- A side note (nitpick, etc.); it's Friday night in here, I'm enjoying my beer; so maybe I'm wrong about the whole thing. > @@ -553,6 +553,7 @@ void __handle_sysrq(int key, bool check_mask) > op_p->handler(key); > } else { > pr_cont("This sysrq operation is disabled.\n"); > + console_loglevel = orig_log_level; > } This looks a bit racy. When we do printk("FOO\n"); console_loglevel = XYZ; We don't have any real guarantees that printk("FOO\n") will print anything straight ahead. It is possible that console_sem is already locked and the owner is preempted, so by the time the console_sem owner picks up that FOO\n messages, console_loglevel is back to orig_log_level and suppress_message_printing() will just tell us to skip the message. Do we need pr_cont() there? Maybe we can just have a normal pr_err() which would always tell that "key" sysrq is disabled? (we also would need to change the error message a bit). -ss