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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 7EBDCC04EB8 for ; Wed, 12 Dec 2018 11:08:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3EA4F20870 for ; Wed, 12 Dec 2018 11:08:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544612922; bh=PDrtaN6cQnbKfzkNqPknBmaLeK+OqifZ2wMk4R/tvLI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=No8mHYm1Jh9pMIUlMo/ZJ2IEtjzTrmWoE7cU/1DoAJM6DxR0qaaxkmd7uMNaNmgZs 9lAt+fd4RVrJRUe5Bbgl9Mm4YKc1HuIfppDUbbPPNpM0i4yyLPHpXDrr+Wn3R9H8qz TNZS4wzbsbMzgOzBYdFL+9EOxvJEfuRVC0zsVT5Q= DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3EA4F20870 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org 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 S1727275AbeLLLIl (ORCPT ); Wed, 12 Dec 2018 06:08:41 -0500 Received: from mail.kernel.org ([198.145.29.99]:41888 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726856AbeLLLIl (ORCPT ); Wed, 12 Dec 2018 06:08:41 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D17DD2084E; Wed, 12 Dec 2018 11:08:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544612920; bh=PDrtaN6cQnbKfzkNqPknBmaLeK+OqifZ2wMk4R/tvLI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=e8mQFG9fjB6cys6l/uDi9eBWRIqiV8v3/aY6EUvy4ska6JL8gDKbDlbk/xT0ch7Eq 4Pri3BN31+4UEsgoSGNmPuSpfKC27M/oG389YXRSKIhFAD/JXDny3e9Ir5o2/AJlzf 8mEbn+YIsNQ7JFN+chukEP8+EMvhMdWhsmVmYTg4= Date: Wed, 12 Dec 2018 12:08:38 +0100 From: Greg Kroah-Hartman To: Sergey Senozhatsky Cc: Petr Mladek , Steven Rostedt , Jiri Slaby , linux-kernel@vger.kernel.org, Daniel Wang , Peter Zijlstra , Andrew Morton , Linus Torvalds , Alan Cox , Peter Feiner , linux-serial@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC][PATCHv2 3/4] serial: introduce uart_port locking helpers Message-ID: <20181212110838.GA11361@kroah.com> References: <20181016050428.17966-1-sergey.senozhatsky@gmail.com> <20181016050428.17966-4-sergey.senozhatsky@gmail.com> <20181208031249.GA443@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181208031249.GA443@jagdpanzerIV> 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 Sat, Dec 08, 2018 at 12:12:49PM +0900, Sergey Senozhatsky wrote: > 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? If done in a sane manner, no objection from me.