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 65C8DC433FE for ; Tue, 15 Nov 2022 18:36:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230106AbiKOSgN (ORCPT ); Tue, 15 Nov 2022 13:36:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229841AbiKOSgK (ORCPT ); Tue, 15 Nov 2022 13:36:10 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AA2FACD7 for ; Tue, 15 Nov 2022 10:36:08 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 682371F892; Tue, 15 Nov 2022 18:36:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668537367; 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=5XQ2sJiljidryJdoIX8oswLfwoui4/Bu1nty4gymX/8=; b=A54A9+xGYc9OqUV7vdGFpmQszxhIQ5tBZfxPrAFLJU/6sqMDjpsKmb+sp6gK26PhlhWZth UbxIY2+tdWrG/rsLHT/Y7o6M851tdNGpwDMmIxgypa1r4rlq3JQUz/RtM91OF2UGFcAahn 2ZkWsS755qohpy6R1hYsq9qxhKp0U8I= 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 497222C149; Tue, 15 Nov 2022 18:36:07 +0000 (UTC) Date: Tue, 15 Nov 2022 19:36:06 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: replay log: Re: [PATCH printk v4 38/39] printk: relieve console_lock of list synchronization duties Message-ID: References: <20221114162932.141883-1-john.ogness@linutronix.de> <20221114162932.141883-39-john.ogness@linutronix.de> <87r0y4m955.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r0y4m955.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 2022-11-15 18:21:34, John Ogness wrote: > On 2022-11-15, Petr Mladek wrote: > >>> --- a/kernel/printk/printk.c > >>> +++ b/kernel/printk/printk.c > >>> @@ -3334,6 +3330,11 @@ void register_console(struct console *newcon) > >>> * boot console that is the furthest behind. > >>> */ > >>> if (bootcon_registered && !keep_bootcon) { > >>> + /* > >>> + * Hold the console_lock to guarantee safe access to > >>> + * console->seq. > >>> + */ > >>> + console_lock(); > >>> for_each_console(con) { > >>> if ((con->flags & CON_BOOT) && > >>> (con->flags & CON_ENABLED) && > >>> @@ -3341,6 +3342,7 @@ void register_console(struct console *newcon) > >>> newcon->seq = con->seq; > >>> } > >>> } > >>> + console_unlock(); > > > > So, without the above two hunks: > > > > Reviewed-by: Petr Mladek > > Note that we actually need those hunks to guarantee a consistent @seq > value. The console_lock is the only synchronization mechanism available > to read console->seq. Yes, we need a solution. But it does not need to be in this patch. This patch removes console_lock() on some locations. But this particular code was called without console_lock() even before this patch. Note that the regression was added in the 3rd patch that moved this code outside console_lock(). Maybe, the easiest solution would be to do in the 3rd patch [*]: } else { /* Begin with next message. */ newcon->seq = prb_next_seq(prb); /* * Try hard to show the pending messages on boot consoles. * so that the new console does not start too late. */ pr_flush(); } It should behave as good and as bad as the original code. [*] Or move the code and add this change before the 3rd patch to keep this questionable solution separated and avoid the regression. Best Regards, Petr