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 BD1DCC4332F for ; Tue, 15 Nov 2022 10:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238400AbiKOKvo (ORCPT ); Tue, 15 Nov 2022 05:51:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232690AbiKOKuz (ORCPT ); Tue, 15 Nov 2022 05:50:55 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6D6C321E23 for ; Tue, 15 Nov 2022 02:50:35 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 21BD81F8B5; Tue, 15 Nov 2022 10:50:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668509434; 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=/FTzh3IqYnsvgJzPb6LH/DCDSa8tDLbBI2Cl4le4c+k=; b=clQHvMuYUmo0CX84Qp1eGE9cTD09zVwxq2prklM6iZ2FuKryLC4kXT5f0w90oG64MeRI+F UB9sh+z2SnRCSwxkI74rIZ5IhTuUP5U+6SuSaX+0Pg6aUQnY+RsEs7HXniFUVW22u6MFU0 QgmZMnc6/95IeIQlaUHA/yeX1+w9ISs= 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 C19E82C142; Tue, 15 Nov 2022 10:50:33 +0000 (UTC) Date: Tue, 15 Nov 2022 11:50:32 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221114162932.141883-4-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. Best Regards, Petr > > /* > * > @@ -3269,6 +3318,14 @@ int unregister_console(struct console *console) > console_first()->flags |= CON_CONSDEV; > > console_unlock(); > + > + /* > + * Ensure that all SRCU list walks have completed. All contexts > + * must not be able to see this console in the list so that any > + * exit/cleanup routines can be performed safely. > + */ > + synchronize_srcu(&console_srcu); > + > console_sysfs_notify(); > > if (console->exit) > -- > 2.30.2