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 BE2CDC4332F for ; Tue, 15 Nov 2022 11:34:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237805AbiKOLej (ORCPT ); Tue, 15 Nov 2022 06:34:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237845AbiKOLeL (ORCPT ); Tue, 15 Nov 2022 06:34:11 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AE3AD27FE3 for ; Tue, 15 Nov 2022 03:33:21 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1668511998; h=from:from:reply-to:subject:subject: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=84NxScZ/MpXsb6BzINZ3D5GdsaYfcLEsVFFGhZDaqNs=; b=ts5xpgloRXL6Bunef+ZM/bPFUqmdLJR9Fj0gjVcG20l9/BfANk1rz82SZRCUgQBgX//850 Ap8HafTsPFCj2AZHXPDPDECyWxITIwYNjLlyZjk+vNMGyA6YiXfGcyISY7CF+L74gx8zjF 4vIZkUAgwW+wI3Mxq2O4of7SB6H3KQV6gjlB02xGpAwHEYy+OVvZNvV7J2jnfwQZQN/hsm jEB9UlqjTJ+5sI917o0GbbI6iSCAxrzY594W+Usbq0C4XkPco6HrTnk/seqmXyYJOPgwGz FD8Wl6tTIwTT395I1vX0WbWGVFAPljWiELKwlWH3JJebNigzm9l/v5W9A4dsOA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1668511998; h=from:from:reply-to:subject:subject: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=84NxScZ/MpXsb6BzINZ3D5GdsaYfcLEsVFFGhZDaqNs=; b=fDpUTw9c7fbDdNnYcH2Vuqv+sl7xjT616YBgKGInE1iEr7jAFZA1j8ks1dC3zwkU+1T7Lr 2PYhwVIbuP7HqNAA== To: Petr Mladek 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 In-Reply-To: References: <20221114162932.141883-1-john.ogness@linutronix.de> <20221114162932.141883-4-john.ogness@linutronix.de> Date: Tue, 15 Nov 2022 12:39:18 +0106 Message-ID: <875yfgo3k1.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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. John