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 F1EA4C43441 for ; Mon, 26 Nov 2018 04:57:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A93182086B for ; Mon, 26 Nov 2018 04:57:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RKMf66MH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A93182086B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.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 S1726252AbeKZPuH (ORCPT ); Mon, 26 Nov 2018 10:50:07 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:41040 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726145AbeKZPuH (ORCPT ); Mon, 26 Nov 2018 10:50:07 -0500 Received: by mail-pl1-f194.google.com with SMTP id u6so13263182plm.8 for ; Sun, 25 Nov 2018 20:57:13 -0800 (PST) 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=ImIdEz/mSkGGs8h9Uvsojw5yvuiE8ggzgSltd/tEqUQ=; b=RKMf66MHq2soXopaTKq+9jn6oh07zSvirDzhx43yXZYeWZ1E/gtYgFrzNJCVYF/ixR kvA3DADurE/GMX/gYtN7FVN1YWxZ8bWKwB8AHay+BV1I2AS40X+22A2/H4nobvFEUN9U b0+zm5CwotWCfo4m6ajhrVyrtNGwh5HShmLsjxkqLiVjYzwwPP7po8U4UocP0K01zamL FV7t9Yujl8Y64BHFKz4iA741GET62XHhoZtXv1+hVA9oKiCWeyhHZ8SL+9T889Tbcncq 1+hUIqS53hlGWDA2xwIvxo5mhnVix/4pIBNF/gTNuD2xTfnqa27A93nmdX6MVGS8dblL xRPQ== 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=ImIdEz/mSkGGs8h9Uvsojw5yvuiE8ggzgSltd/tEqUQ=; b=OLu8oH1s1WfT7ZasjXjMZSOvwh+4Y9+etjGhpmGpeI1axwmnf6tRXGzLNKZ2mHxJGg NLcCwhqKYJnquMsyqPjhiMasbIpb6dN3uUpfDoTlL2axn6jcB+Z6h3SFDBk/XxvXm3Qp 86FnAfY0gjG/ZaHNg0cuVRHyvhiZ/7KGHZnAcVxJRc1IwvMi++k+0DfISJ5JgtlbPxRw R44L9qlacjHHdXnGO7g4RDn4WxHxhfLqRaoDlpFHDi/PDa/f/9hJPmexAH2WZN933YLb HoQSK3CWsOOACXb2V0n4WTv5whLjQG6Qa9x+S93DiczpEF80/V2JaD9NlTUEJ35acsL3 xX2A== X-Gm-Message-State: AA+aEWYh8HitF85VuxGAx18/t3Hnok4oUnwDHZsWgY7Wng05nLqXGcY1 jrBxLPW7kdK3JjTJ4zDJXDfgKKa2 X-Google-Smtp-Source: AFSGD/U+ovqUhxfxsfpWL/sCejJc1X61NQxzstox6Lo8gMdY/VAFH9wnRWMurhjCmVEMGzSKg3Oz8Q== X-Received: by 2002:a17:902:50e3:: with SMTP id c32mr26226364plj.318.1543208232966; Sun, 25 Nov 2018 20:57:12 -0800 (PST) Received: from localhost ([175.223.33.236]) by smtp.gmail.com with ESMTPSA id d25sm3949276pfe.40.2018.11.25.20.57.11 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 25 Nov 2018 20:57:11 -0800 (PST) Date: Mon, 26 Nov 2018 13:57:09 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: Sergey Senozhatsky , Peter Zijlstra , Waiman Long , Ingo Molnar , Will Deacon , Thomas Gleixner , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Sergey Senozhatsky , Andrey Ryabinin , Tejun Heo , Andrew Morton , Steven Rostedt Subject: Re: [PATCH v2 07/17] debugobjects: Move printk out of db lock critical sections Message-ID: <20181126045709.GD540@jagdpanzerIV> References: <1542653726-5655-1-git-send-email-longman@redhat.com> <1542653726-5655-8-git-send-email-longman@redhat.com> <2ddd9e3d-951e-1892-c941-54be80f7e6aa@redhat.com> <20181122020422.GA3441@jagdpanzerIV> <20181122101606.GP2131@hirez.programming.kicks-ass.net> <20181123024048.GD1582@jagdpanzerIV> <20181123114826.h27t7qiwfp7grrqx@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181123114826.h27t7qiwfp7grrqx@pathway.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (11/23/18 12:48), Petr Mladek wrote: [..] > > This should make serial consoles re-entrant. > > So printk->console_driver_write() hopefully will not deadlock. > > Is the re-entrance safe? Some risk might be acceptable in Oops/panic > situations. It is much less acceptable for random warnings. Good question. But what's the alternative? A deadlock in a serial console driver; such that even panic() is not guaranteed to make through it (at least of now). debug objects are used from the code which cannot re-entrant console drivers. bust_spinlock is called from various paths, not only panic. git grep bust_spinlocks | wc -l 62 So we already switch to re-entrant consoles (and accept the risks) in mm/fault.c, kernel/traps.c and so on. Which, I guess, makes us a little more confident, faults/traps happen often enough. It seems, that, more or less, serial consoles are ready to handle it. UART consoles in ->write() callbacks just do a bunch of writel() [for every char + \r\n]. -ss