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 BC493C04EB8 for ; Sat, 8 Dec 2018 03:12:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7694020857 for ; Sat, 8 Dec 2018 03:12:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="QuXsAJkn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7694020857 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 S1726110AbeLHDM4 (ORCPT ); Fri, 7 Dec 2018 22:12:56 -0500 Received: from mail-pg1-f193.google.com ([209.85.215.193]:36474 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726065AbeLHDM4 (ORCPT ); Fri, 7 Dec 2018 22:12:56 -0500 Received: by mail-pg1-f193.google.com with SMTP id n2so2527851pgm.3; Fri, 07 Dec 2018 19:12:55 -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=Z1WvjBE9TdQi1/UOYy0m2Iepa4cbtGhJBZpeen9wgBA=; b=QuXsAJkn1Lxudeme/8BedD4TsfL98fJa1tXBFdwKE/ub3ybjAVsWiU2ikdXR4cS1Op tza2NPd13ysakZNYTekhW6m4d+XjYpGM7N3XoqHjXQPEXtfXeNytvVxELwYTOdh5xylx Qfphs3LFOheXtlXwSDUEMDC8rZ79MXlAgLOFQKU+IaMnR5iNRANXAn+huDb+06+WtbUc MbpvQFPWLc5m/yWCDVIG8gb2j/uChaf/ToMxBcFwC8DmRJ+Jr86/CWafB0XdXB6uhh8c Mx0vgmvx9qrVrHI8x32YH8Kz5s5zrxlSH9T15ZgU07Krw+aDJtpsSy0ey/LZnzPGbIF6 7mbQ== 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=Z1WvjBE9TdQi1/UOYy0m2Iepa4cbtGhJBZpeen9wgBA=; b=ihVIuih8HBVg4NlUC2tynjijcFLlSHdM9xrV0Bke7QlQutfGc6io8F7S3ehuRUPnSm c1jaEcPGBxe/0HMyiaXqJYbPJzJsP7e97lN1lR0Xtag+cz8f18rbopcBryYjTek8KpiD gAGwOGOLlYCfil0WimNNTvr1HPOcXQeRflEzELnFtpGvVpveaBmMMnCVtagTxRf6JVMO rf4m0NrGxHWC2yRczfjog/FxlxT2yDVJ+LOww5qG+B/7zNrXJrrGW34kSS239ODnE4OH DBLSizJfXJ374fogprjT+UShoxDz4xwQAI+wF0pKGHoCn9R23gPIJ8OVg4+ZShlsCvOs j9dA== X-Gm-Message-State: AA+aEWZvMeyDJvywN6ArMtpO283jOslf0vL03m65Vif62e/Ix0gsdH9f poblSS+1XuQoeLV1jDTttaM= X-Google-Smtp-Source: AFSGD/Vv2Tpj3ACeR/yomwFSHTW1Mh7U9tKcCdHpWv3O9/0oHISvzFJRzUKreHYjla1yU/IalyYhCQ== X-Received: by 2002:a62:2044:: with SMTP id g65mr4578602pfg.127.1544238774980; Fri, 07 Dec 2018 19:12:54 -0800 (PST) Received: from localhost ([175.223.33.43]) by smtp.gmail.com with ESMTPSA id a15sm5174103pgb.1.2018.12.07.19.12.52 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 07 Dec 2018 19:12:53 -0800 (PST) Date: Sat, 8 Dec 2018 12:12:49 +0900 From: Sergey Senozhatsky To: Petr Mladek , Steven Rostedt , Greg Kroah-Hartman , Jiri Slaby Cc: linux-kernel@vger.kernel.org, Daniel Wang , Peter Zijlstra , Andrew Morton , Linus Torvalds , Alan Cox , Peter Feiner , linux-serial@vger.kernel.org, Sergey Senozhatsky , Sergey Senozhatsky Subject: Re: [RFC][PATCHv2 3/4] serial: introduce uart_port locking helpers Message-ID: <20181208031249.GA443@jagdpanzerIV> References: <20181016050428.17966-1-sergey.senozhatsky@gmail.com> <20181016050428.17966-4-sergey.senozhatsky@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181016050428.17966-4-sergey.senozhatsky@gmail.com> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (10/16/18 14:04), Sergey Senozhatsky wrote: [..] > - The first entry point is console ->write() callback, which we call > from printk(). A possible deadlock scenario there is: > > CPU0 > > spin_lock_irqsave(&port->lock, flags) << deadlock > serial_foo_write() > call_console_drivers() > console_unlock() > console_flush_on_panic() > panic() > > spin_lock_irqsave(&port->lock, flags) > serial_foo_write() > call_console_drivers() > console_unlock() > printk() > ... [..] > - The rest (of entry points) requires a bit different handling. > Let's take a look at the following backtrace: > > CPU0 > > spin_lock_irqsave(&port->lock, flags) << deadlock > serial_foo_write() > call_console_drivers() > console_unlock() > printk() > __queue_work() > tty_flip_buffer_push() > spin_lock_irqsave(&port->lock, flags) > serial_foo_handle_IRQ() > > > Serial drivers invoke tons of core kernel functions - WQ, MM, etc. All > of which may printk() in various cases. So we can't really just > "remove those printk-s". The simples way to address this seems to be > PRINTK_SAFE_CONTEXT_MASK. serial/UART and printk guys, sorry to bother you, do you hate this idea of removing console_driver->CORE KERNEL->printk->console_driver deadlock path? Or is there any chance we can move forward? -ss