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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31BD9C54EBD for ; Fri, 13 Jan 2023 02:32:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231400AbjAMCct (ORCPT ); Thu, 12 Jan 2023 21:32:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55554 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232586AbjAMCcs (ORCPT ); Thu, 12 Jan 2023 21:32:48 -0500 Received: from mail-pf1-x430.google.com (mail-pf1-x430.google.com [IPv6:2607:f8b0:4864:20::430]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A22C25D6A2 for ; Thu, 12 Jan 2023 18:32:47 -0800 (PST) Received: by mail-pf1-x430.google.com with SMTP id s3so12672520pfd.12 for ; Thu, 12 Jan 2023 18:32:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=kOmM1boioYg8LFtWAWs33j4bBuyb4KtgIsQ+w3Q1Nec=; b=Ms+uSdJMIWu+6/rPfkBxkXAr7MPZBipnJfzVJqCmg773hVvxRx+OKl/7d0nRAxXsTX oJrqG0gxih/ylYXorRI2xrOT6BC9zp2wrZANpID7nHNl7KGadbiX7PDfPfrpxIEmncPH +KS+1pR7XE/gs4blQKXKoaKeorMh34AzE1BA8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=kOmM1boioYg8LFtWAWs33j4bBuyb4KtgIsQ+w3Q1Nec=; b=MO8lBr8BDOAmxgWtxzvGXaYfIuREVqbOzaot9OiMYVddN4fRk5LiwGbbTLiwmjjsVK tsCzzf+BeEbfQYcIxlQwcmBNrMRJSYDonvp9d/1dyAUrE4t1MGj4BAiMXSJEqUu8v00T tpiktMhtJY0mcPfdFeLdxxp2tu0J3R1BUwlrMpv5xIJb6edOFE9awmbQWuhhBbqcI/Bd uIL/r6WcW1Nb4vd6LVBIk1iTiAfpt8gwqJo8l/+AK2ch+U5/bz8YhE2XsqrnbFVOIDIi brm+Yl9T9z8BKYZmnAqQcPt+Mf8JlTfyPbQw57TOv4z+azXRLG1qAySP1OZ51n9q2sc9 N8oQ== X-Gm-Message-State: AFqh2kp2MD3PFQdjL7NKa8Rv3YVGghh0fRgwEb8Q63XFkmZ7hR9m4PnQ s1X9lVyRc4tyI+00g9I32GpHBeWqGKXM2rGg X-Google-Smtp-Source: AMrXdXtDHCAjBbBXjeoIpHmcmPAFTDOvNbFwRTgswr8/FoRJEOP33+VktonH7fugm95/k2TxfeSk3A== X-Received: by 2002:a62:e703:0:b0:577:7cfb:a896 with SMTP id s3-20020a62e703000000b005777cfba896mr8682396pfh.31.1673577167232; Thu, 12 Jan 2023 18:32:47 -0800 (PST) Received: from google.com (KD124209188001.ppp-bb.dion.ne.jp. [124.209.188.1]) by smtp.gmail.com with ESMTPSA id y22-20020aa78f36000000b00562677968aesm12568828pfr.72.2023.01.12.18.32.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Jan 2023 18:32:46 -0800 (PST) Date: Fri, 13 Jan 2023 11:32:41 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Jason Wessel , Daniel Thompson , Douglas Anderson , Greg Kroah-Hartman , Jiri Slaby , kgdb-bugreport@lists.sourceforge.net, linux-serial@vger.kernel.org Subject: Re: [PATCH] tty: serial: kgdboc: fix mutex locking order for configure_kgdboc() Message-ID: References: <20230111145110.1327831-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On (23/01/12 16:40), Petr Mladek wrote: > On Wed 2023-01-11 17:23:55, Petr Mladek wrote: > > On Wed 2023-01-11 15:57:10, John Ogness wrote: > > > Several mutexes are taken while setting up console serial ports. In > > > particular, the tty_port->mutex and @console_mutex are taken: > > > > > > serial_pnp_probe > > > serial8250_register_8250_port > > > uart_add_one_port (locks tty_port->mutex) > > > uart_configure_port > > > register_console (locks @console_mutex) > > > > > > In order to synchronize kgdb's tty_find_polling_driver() with > > > register_console(), commit 6193bc90849a ("tty: serial: kgdboc: > > > synchronize tty_find_polling_driver() and register_console()") takes > > > the @console_mutex. However, this leads to the following call chain > > > (with locking): > > > > > > platform_probe > > > kgdboc_probe > > > configure_kgdboc (locks @console_mutex) > > > tty_find_polling_driver > > > uart_poll_init (locks tty_port->mutex) > > > uart_set_options > > > > > > This is clearly deadlock potential due to the reverse lock ordering. [..] > > > - console_list_lock(); > > > - > > > p = tty_find_polling_driver(cptr, &tty_line); > > > if (!p) { > > > console_list_unlock(); > > > > This console_list_unlock() should be removed here as well. > > This seems to be the only problem. Otherwise, the patch looks good to > me. Good catch. Reviewed-by: Sergey Senozhatsky