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 B482EC433FE for ; Thu, 10 Nov 2022 12:58:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229843AbiKJM6M (ORCPT ); Thu, 10 Nov 2022 07:58:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53772 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229542AbiKJM6K (ORCPT ); Thu, 10 Nov 2022 07:58:10 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E611B71F35 for ; Thu, 10 Nov 2022 04:58:09 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 937261FAD3; Thu, 10 Nov 2022 12:58:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668085088; 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=cvkRMglln4HBHPX98O0sRdjNj682jRwZGliLDUK9dqQ=; b=EtnfcATI9xCVDi+aTJrCuXHOgJCSLKRmd0qPgMS4MgpEzAN7e6LTugvbpISeS3oRQuClQb xiqKmZyIfBfvzv0J0l4TAjvbSiWI4kP8mFFPxHkWxLcLvFMidfc2Hr6xASAKtIySMkxiQl ySwSfL1f5XfHOR0C0O2shcOOaJwbFpU= 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 3CEA62C141; Thu, 10 Nov 2022 12:58:08 +0000 (UTC) Date: Thu, 10 Nov 2022 13:58:07 +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 v3 21/40] printk: introduce console_list_lock Message-ID: References: <20221107141638.3790965-1-john.ogness@linutronix.de> <20221107141638.3790965-22-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221107141638.3790965-22-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 2022-11-07 15:22:19, 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 Best Regards, Petr