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 33CF5C43217 for ; Mon, 21 Nov 2022 13:36:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230408AbiKUNg3 (ORCPT ); Mon, 21 Nov 2022 08:36:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231129AbiKUNgU (ORCPT ); Mon, 21 Nov 2022 08:36:20 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79C6CC2843 for ; Mon, 21 Nov 2022 05:36:16 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 40524220C2; Mon, 21 Nov 2022 13:36:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1669037775; 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=dOP7gLTrtKFMqQ0Yy0qoL3B++G+/cztXu069nQpDp24=; b=Ij6zliOBjjUnbU16Xnxg6jUBLKF9cqsbynCwsSahhJGYS0PwiVTp3Cz33sFeWGk9GywJbD PbzeXoFWDRczYIT27bSoYXMon0+s29JGg49uZi37CAy65rN2WTBtA7YhCzR3d51JWnSuv3 3sBfM2jxxrxcCiM+EbF1L3E0tGaMDL8= Received: from suse.cz (unknown [10.100.201.202]) (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 E133D2C14B; Mon, 21 Nov 2022 13:36:14 +0000 (UTC) Date: Mon, 21 Nov 2022 14:36:14 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: Re: [PATCH printk v6 11/40] printk: introduce console_list_lock Message-ID: References: <20221116162152.193147-1-john.ogness@linutronix.de> <20221116162152.193147-12-john.ogness@linutronix.de> <87sficwokr.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sficwokr.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 2022-11-21 12:16:12, John Ogness wrote: > Currently there exist races in register_console(), where the types > of registered consoles are checked (without holding the console_lock) > and then after acquiring the console_lock, it is assumed that the list > has not changed. Also, some code that performs console_unregister() > make similar assumptions. > > It might be possible to fix these races using the console_lock. But > it would require a complex analysis of all console drivers to make > sure that the console_lock is not taken in match() and setup() > callbacks. And we really prefer to split up and reduce the > responsibilities of console_lock rather than expand its complexity. > Therefore, introduce a new console_list_lock to provide full > synchronization for any console list changes. > > In addition, also use console_list_lock for synchronization of > console->flags updates. All flags are either static or modified only > during the console registration. There are only two exceptions. > > The first exception is CON_ENABLED, which is also modified by > console_start()/console_stop(). Therefore, these functions must > also take the console_list_lock. > > The second exception is when the flags are modified by the console > driver init code before the console is registered. These will be > ignored because they are not visible to the rest of the system > via the console_drivers list. > > Note that one of the various responsibilities of the console_lock is > also intended to provide console list and console->flags > synchronization. Later changes will update call sites relying on the > console_lock for these purposes. Once all call sites have been > updated, the console_lock will be relieved of synchronizing > console_list and console->flags updates. > > Suggested-by: Thomas Gleixner > Signed-off-by: John Ogness > Reviewed-by: Petr Mladek > --- > Stephen reported [0] a build failure with linux-next. The problem was a > missing EXPORT of @lockdep_assert_console_list_lock_held for when > drivers are built as modules. > > [0] https://lore.kernel.org/lkml/20221121110041.1d2c635b@canb.auug.org.au JFYI, the branch rework/console-list-lock in printk/linux.git has been rebased using this version of the patch. Thanks a lot for the fix. Best Regards, Petr