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 D887AC4332F for ; Thu, 10 Nov 2022 17:27:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231823AbiKJR1D (ORCPT ); Thu, 10 Nov 2022 12:27:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230493AbiKJR0w (ORCPT ); Thu, 10 Nov 2022 12:26:52 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E173F18E37; Thu, 10 Nov 2022 09:26:50 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 9FD55228D3; Thu, 10 Nov 2022 17:26:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668101209; 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=Nzyi44WKO3p/rhzOL3lGsqVjLxzcpLoKQVlmwsHqaY4=; b=VIifZ/vuAtq6adyPtfIzER7lD6dcovCYFn2LPl2N7liyeJ2smk+e619717bVZOVG2cCs4L 4NW34hAc5nZGPOp/hx+KHmTKMgvXYz+r6z8waJ7yaz+ZDQCc5GlM2IINXZtTuek5vPZ+hB 8h++xOtr6IViY8n5P15stCuy6lMKTek= 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 3D2E22C141; Thu, 10 Nov 2022 17:26:49 +0000 (UTC) Date: Thu, 10 Nov 2022 18:26:48 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Helge Deller , Greg Kroah-Hartman , Javier Martinez Canillas , Thomas Zimmermann , Juergen Gross , Boris Ostrovsky , Tom Rix , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH printk v3 33/40] printk, xen: fbfront: create/use safe function for forcing preferred Message-ID: References: <20221107141638.3790965-1-john.ogness@linutronix.de> <20221107141638.3790965-34-john.ogness@linutronix.de> <877d026blr.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877d026blr.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org On Thu 2022-11-10 17:09:12, John Ogness wrote: > On 2022-11-10, Petr Mladek wrote: > >> +void console_force_preferred_locked(struct console *con) > >> +{ > >> + struct console *cur_pref_con; > >> + > >> + if (!console_is_registered_locked(con)) > >> + return; > >> + > >> + cur_pref_con = console_first(); > >> + > >> + /* Already preferred? */ > >> + if (cur_pref_con == con) > >> + return; > >> + > >> + hlist_del_init_rcu(&con->node); > > > > We actually should re-initialize the node only after all existing > > console list walks are finished. Se we should use here: > > > > hlist_del_rcu(&con->node); > > hlist_del_init_rcu() only re-initializes @pprev pointer. Ah, I was not aware of it. > But maybe you > are concerned that there is a window where list_unhashed() becomes true? > I agree that it should be changed to hlist_del_rcu() because there > should not be a window where this console appears unregistered. Makes sense. > >> + /* Only the new head can have CON_CONSDEV set. */ > >> + WRITE_ONCE(cur_pref_con->flags, cur_pref_con->flags & ~CON_CONSDEV); > > > > As mentioned in the reply for 7th patch, I would prefer to hide this > > WRITE_ONCE into a wrapper, e.g. console_set_flag(). It might also > > check that the console_list_lock is taken... > > Agreed. For v4 it will become: > > console_srcu_write_flags(cur_pref_con->flags & ~CON_CONSDEV); I am happy that your are going to introduce an API for this. Just to be sure. The _srcu_ in the name means that the write will use WRITE_ONCE() so that it can be read safely in SRCU context using READ_ONCE(). Do I get it correctly, please? I expect that the counter part will be console_srcu_read_flags(). I like the name. It is better than _unsafe_ that I proposed earlier. Best Regards, Petr