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 671BBC43381 for ; Wed, 13 Mar 2019 02:15:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 30DFF217F5 for ; Wed, 13 Mar 2019 02:15:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="V6EuGMPd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726792AbfCMCPj (ORCPT ); Tue, 12 Mar 2019 22:15:39 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:33921 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726384AbfCMCPj (ORCPT ); Tue, 12 Mar 2019 22:15:39 -0400 Received: by mail-pf1-f194.google.com with SMTP id v64so273004pfb.1; Tue, 12 Mar 2019 19:15:38 -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=ddHuCc5raQ90r/bsCgad0VSKP/YEFC4aYtxhp/GMEXc=; b=V6EuGMPdh2uCj7aEfwnXwkDvag2HMTh3nTeQ+EYKaa3/4TvGRFjDGNmpBEYG4f2+L8 7/3UjUnx8hyNOG/aFjVNZtvDzkZ8EAxwxA4z4XFKwz9OEHDC3rYG10iLixoyXF019EnN k7ooDlkNnqxqNxzCvmrEVrMLjgnRT/rwfga0UyGRfLfYRsXsudFJqq7EX6XqUlTHOAHc OHPXivkrepUTwPLoSiJfQUz0MVZzzD5rIt4ljKcFKzipi9rZ9DvzzPbv+N8Ljayak7Y1 Dj7npnFLy6Tbvmwl+Z3eq44Xzj7VcGCbykmkUuliAaeSppFyv38nxhhFZK+w537YC3HY iEAA== 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=ddHuCc5raQ90r/bsCgad0VSKP/YEFC4aYtxhp/GMEXc=; b=io46H/+pCb2kdX9mNM5ecBnP4Tilz8rgJxmIiBGEtnx6LpMKoegk3pWpArLnas6hVX lFeKtSAgJmraewZfsQ4K+ArHPGKcpCMx5ISli/lr+OnZkJi10IohTOLrHkCZHVZ7XH7E cmzRpvkOiGmT6ZAIAh8JdNoKZ4+rTeWZNnJs27s1E86j8Ho9a0dmNmdhOrRGG/EDd7df g62goCWbY2N12n9s9cmOV0TVIQKLj9wX+iBU5sQA18NRMbNgdQ9zsyxiyX7dWdLsUiyg N1jNi8JEjMPTtxUbX4zH/n2pMV1E7VtCgm8+z7X6kfwAYFdGcPGvu/I5oJwTzbgcPlm3 Aarw== X-Gm-Message-State: APjAAAWz/g9grNqwO9mhL4KrrAjxiP5nqGu/uDAaNI/JB2Y/33LT8k3t YNvcwfBSzwgZ4TgLgpMFsV+2FCzc X-Google-Smtp-Source: APXvYqy0l21xROQJQ+6JQW0LzJsYHQE1TrbvjvcWDGyOWyCWBYwepJkE666KJ1UNlJXHCKZR97Nt+g== X-Received: by 2002:a17:902:9a95:: with SMTP id w21mr42727912plp.118.1552443338143; Tue, 12 Mar 2019 19:15:38 -0700 (PDT) Received: from localhost ([110.70.15.13]) by smtp.gmail.com with ESMTPSA id o5sm6221809pgc.16.2019.03.12.19.15.36 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 12 Mar 2019 19:15:37 -0700 (PDT) Date: Wed, 13 Mar 2019 11:15:34 +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 , Sebastian Siewior Subject: Re: [RFC PATCH v1 00/25] printk: new implementation Message-ID: <20190313021534.GB783@jagdpanzerIV> References: <20190212143003.48446-1-john.ogness@linutronix.de> <20190213025520.GA5803@jagdpanzerIV> <874l9721hf.fsf@linutronix.de> <20190304052335.GA6648@jagdpanzerIV> <87lg1rggcz.fsf@linutronix.de> <20190311105411.GA368@jagdpanzerIV> <20190312123857.juatd6fwtfmqajze@pathway.suse.cz> <874l8815uc.fsf@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874l8815uc.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 (03/12/19 16:15), John Ogness wrote: > > I suggest the following way forward (separate patchsets): > > > > 1. Replace log buffer (least controversial thing) > > Yes. I will post a series that only implements the ringbuffer using your > simplified API. That will be enough to remove printk_safe and actually > does most of the work of updating devkmsg, kmsg_dump, and syslog. This may _not_ be enough to remove printk_safe. One of the reasons printk_safe "condom" came into existence was console_sem (which is a bit too important to ignore it): printk() console_trylock() console_unlock() up() raw_spin_lock_irqsave(&sem->lock, flags) __up() wake_up_process() WARN/etc printk() console_trylock() down_trylock() raw_spin_lock_irqsave(&sem->lock, flags) << deadlock Back then we were looking at printk->console_sem->lock->printk->console_sem->lock deadlock report from LG, if I'm not mistaken. -ss