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 D700BC54EBC for ; Thu, 12 Jan 2023 15:52:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240487AbjALPw3 (ORCPT ); Thu, 12 Jan 2023 10:52:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240538AbjALPv4 (ORCPT ); Thu, 12 Jan 2023 10:51:56 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A05046C2B6 for ; Thu, 12 Jan 2023 07:40:36 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 99CF1402C3; Thu, 12 Jan 2023 15:40:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1673538019; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MnhE5SVciJ/SbPnM39oaaCSkXi4rJk4SInUK6g88A8I=; b=gdU4kPBcKFOlGDDkfqP770eiIQG6FQMGlIw9Oyx/L1ICoITOsvbS/4bp/+fghEwhzlgHrr rYIo28C87h7Yus+MmP5RHkuVRzIWlMIMV9jCpyQKU0ahtsQoLgOW6HKgiWxkS00YaB1TI2 qOMeWM9kS897ZqqcSJ5NOFhTmjCmIRA= Received: from suse.cz (unknown [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 1B84C2C141; Thu, 12 Jan 2023 15:40:19 +0000 (UTC) Date: Thu, 12 Jan 2023 16:40:16 +0100 From: Petr Mladek To: John Ogness Cc: 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 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. > > Great catch! > > > Since uart_set_options() requires holding @console_mutex in order to > > serialize early initialization of the serial-console lock, take the > > @console_mutex in uart_poll_init() instead of configure_kgdboc(). > > > > Since configure_kgdboc() was using @console_mutex for safe traversal > > of the console list, change it to use the SRCU iterator instead. > > > > Add comments to uart_set_options() kerneldoc mentioning that it > > requires holding @console_mutex (aka the console_list_lock). > > > > Fixes: 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()") > > Signed-off-by: John Ogness > > > --- a/drivers/tty/serial/kgdboc.c > > +++ b/drivers/tty/serial/kgdboc.c > > @@ -189,15 +190,6 @@ static int configure_kgdboc(void) > > if (kgdboc_register_kbd(&cptr)) > > goto do_register; > > > > - /* > > - * tty_find_polling_driver() can call uart_set_options() > > - * (via poll_init) to configure the uart. Take the console_list_lock > > - * in order to synchronize against register_console(), which can also > > - * configure the uart via uart_set_options(). This also allows safe > > - * traversal of the console list. > > - */ > > - 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. After removing the superfluous console_list_unlock(): Reviewed-by: Petr Mladek John, would you mind to send v2, please? Best Regards, Petr