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 315C1C4332F for ; Tue, 15 Nov 2022 12:04:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236156AbiKOMEo (ORCPT ); Tue, 15 Nov 2022 07:04:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54784 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238263AbiKOMER (ORCPT ); Tue, 15 Nov 2022 07:04:17 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3084EFFB for ; Tue, 15 Nov 2022 04:03:31 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 3F71A1F8B4; Tue, 15 Nov 2022 12:03:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668513809; 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=787wjDZOCndoyFt2mKQ1d7aZ2+xHAJpoA56kFzLmXlQ=; b=CuWLbwz0Vpx5g2oOolZBnnZRoeokXfHLDVaQNE5CxrwqZ38l4wS7rk7eXcU1uOr0vqG6+J li3t4UPue1pzCXRN2WL7+IoddwlEdCDKdS3tGwjHDgZuDwLlAtcWHW1y1EIyvbFT5fnQf2 sYXPl2VPqt4Yhk0SmSM/aCuSMd6EtGw= 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 E170F2C143; Tue, 15 Nov 2022 12:03:28 +0000 (UTC) Date: Tue, 15 Nov 2022 13:03:28 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Miguel Ojeda , Greg Kroah-Hartman , "Paul E . McKenney" Subject: Re: [PATCH printk v4 03/39] printk: Prepare for SRCU console list protection Message-ID: References: <20221114162932.141883-1-john.ogness@linutronix.de> <20221114162932.141883-4-john.ogness@linutronix.de> <875yfgo3k1.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875yfgo3k1.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 2022-11-15 12:39:18, John Ogness wrote: > On 2022-11-15, Petr Mladek wrote: > > On Mon 2022-11-14 17:34:56, John Ogness wrote: > >> Provide an NMI-safe SRCU protected variant to walk the console list. > >> > >> Note that all console fields are now set before adding the console > >> to the list to avoid the console becoming visible by SCRU readers > >> before being fully initialized. > >> > >> This is a preparatory change for a new console infrastructure which > >> operates independent of the console BKL. > >> > >> --- a/kernel/printk/printk.c > >> +++ b/kernel/printk/printk.c > >> @@ -3254,7 +3303,7 @@ int unregister_console(struct console *console) > >> return -ENODEV; > >> } > >> > >> - hlist_del_init(&console->node); > >> + hlist_del_init_rcu(&console->node); > > > > This should be hlist_del_rcu() here so that a list walker that it just > > processing this console could see the rest of the list. > > hlist_del_init_rcu() does not prevent the rest of the list from being > seen. It only unlinks @pprev for future iterators. I see. I looked at hlist_del_init() instead of on the _rcu() variant. hlist_del_init_rcu() is correct here. > > It seems that hlist_unhashed() checks only node.pprev pointer > > so that we even do not need to initialize it. > > > > We discussed this in v3 in the patch implementing > > console_force_preferred_locked(), see > > https://lore.kernel.org/r/Y20aBwNWT19YDeib@alley. > > I forgot that unregister_console() might have the same problem. > > For console_force_preferred_locked() it was about making sure that the > console always appears registered, even though it is temporarily removed > from the console list. > > For unregister_console() we want it to be seen as removed from the > console list. Makes sense. Best Regards, Petr