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=-2.4 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 657DBC43381 for ; Tue, 12 Mar 2019 02:51:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2B4C72087C for ; Tue, 12 Mar 2019 02:51:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Kgqm28YU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726819AbfCLCvi (ORCPT ); Mon, 11 Mar 2019 22:51:38 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:44890 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726406AbfCLCvh (ORCPT ); Mon, 11 Mar 2019 22:51:37 -0400 Received: by mail-pf1-f196.google.com with SMTP id a3so691992pff.11; Mon, 11 Mar 2019 19:51:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=tA9SBm+Jyd/X8VPj7ujDcbfalc7kOHnD2aDkOiE5ong=; b=Kgqm28YU08s/KyNnAhJ2JZd1u1pElhHo460i5oXSCsoQjlt9XpVcmQCS/hPWg8DUTd 4JmAo0PrF4gAFUXK1N+sMJFE+fOLfRIpQetdjO88Vy6DE9ttOmtevyFgPShN7Xa2pddx yz2oVXrBu0fv9/k0EDhbhj2fpLX0soK87yilK0sm8tzPdc0ktq4YGuHGaenVk4CimRnY JFexaCjypP/uso7dxdfq0cwsj6rxObYlxjaVUbXm146wOcytIOhDIUJCEXNR/muanHJq kQFjvjpdLmo8l6iTob3UzASHt9bgtMJHUCSyiWUNFSV+L/ZsKrS8OsiTVuC2QE9jzage 8szw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=tA9SBm+Jyd/X8VPj7ujDcbfalc7kOHnD2aDkOiE5ong=; b=DVIMZzTc0e6bPmTmErkWbLd6e8p1Z8OVbc2fIKfc1UgMTbBvat2U/4EqszYaeAZurl Xp1/3fHwZzdCc+q+gDL8OCw4vdAIXaMOqytSmFyJZl2Z1i3Gr+3jM1OMqwDHLPIFZA5W iwgll1sPQN9ZGRY/bIh4q42tMGysg5xDYFK0Cdzc72Yualti+YED9h+e3siLQ4aEXs4N +eZvGiZeDzfH6XOSdjAIELUih0s3LU0d8DViBXhkbvBnsL+mYGAg/6IeDT3VCQU92zBg bII9Tg1DdTrYy5QW0errwArklqSj7dUQUPlp8S3b4L642KVl1q3ZNbE7JPlOZeVx5VW9 /w5Q== X-Gm-Message-State: APjAAAWDiJkPzCbPPZhHOC0VSpvqGlU9YOQ2nIR9x6sywJtYNZFv3bc2 4k6paYUEbxQSvt5SKYbRO5o= X-Google-Smtp-Source: APXvYqwkPfYsh5H8CmR/yDFxywqDRK3xA47Wq1gvh9PBN1dE8WCsAbc+cHBwbpgJJ6v1WkLgGtZQOA== X-Received: by 2002:a63:104e:: with SMTP id 14mr32735877pgq.185.1552359096930; Mon, 11 Mar 2019 19:51:36 -0700 (PDT) Received: from localhost ([175.223.22.108]) by smtp.gmail.com with ESMTPSA id l19sm9315253pff.185.2019.03.11.19.51.35 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 11 Mar 2019 19:51:36 -0700 (PDT) Date: Tue, 12 Mar 2019 11:51:28 +0900 From: Sergey Senozhatsky To: John Ogness Cc: Petr Mladek , Sergey Senozhatsky , linux-kernel@vger.kernel.org, Peter Zijlstra , Steven Rostedt , Daniel Wang , Andrew Morton , Linus Torvalds , Greg Kroah-Hartman , Alan Cox , Jiri Slaby , Peter Feiner , linux-serial@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC PATCH v1 19/25] printk: introduce emergency messages Message-ID: <20190312025128.GC4146@jagdpanzerIV> References: <20190212143003.48446-1-john.ogness@linutronix.de> <20190212143003.48446-20-john.ogness@linutronix.de> <20190307073029.GA489@jagdpanzerIV> <20190308103127.txsgv3d6lqlf6pad@pathway.suse.cz> <87k1h5zkfn.fsf@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87k1h5zkfn.fsf@linutronix.de> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (03/11/19 13:04), John Ogness wrote: > > Great catch! > > Yes, thanks! > > > I think that it is doable to guard the list using RCU. > > I think it would be enough to take the prb_cpulock when modifying the > console linked list. That will keep printk_emergency() out until the > list has been updated. (registering/unregistering consoles is not > something that happens often.) console_sem can be a bit more than just registering/unregistering. Especially when it comes to VT, fbcon and ioctls. $ git grep console_lock drivers/tty/ | wc -l 82 $ git grep console_lock drivers/video/fbdev/ | wc -l 80 -ss