From patchwork Tue Feb 21 16:15:08 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: John Ogness X-Patchwork-Id: 656197 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 B9163C636D7 for ; Tue, 21 Feb 2023 16:16:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233858AbjBUQQf (ORCPT ); Tue, 21 Feb 2023 11:16:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233775AbjBUQQe (ORCPT ); Tue, 21 Feb 2023 11:16:34 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 906DA2B2AD for ; Tue, 21 Feb 2023 08:16:27 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1676996186; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VUoaKZPiBlB28m/DTeiI2bitW8/6n3bVShBxamKV3uY=; b=zHBzoV5l1lJ3ZjlXVZg/TxSE1Wt3HLwilgoIU+p2E9u98/r/zwFbtynlPiMldfCWG+rdr+ j8jdGbgXcPm9KQjLs+tVmbVuSrPoVlMoy0qRfYmRwX/gCpO408H5qyzZyA8PwZfkEiTQYG xoNoa1Q3JZ+O23gybzbaf49XEfj7Ysl8u/dfnqDccAjMhQzKmpEJRCCqnf42gIOvL2pLJS N8K/U53XjXg9zJjP/RPNwleJaLsQuZJmask8AYfnqIJQ9LcQQbQkZvzeF+37vYxLGQMYoT vd3JWBKuocxp7WXEV5J/sLusaR1ezahc5GkGP8OEXa0hO94CZzVY0aAeJGucwg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1676996186; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VUoaKZPiBlB28m/DTeiI2bitW8/6n3bVShBxamKV3uY=; b=wO0ecSwmkRt/VRjhYBAQAYFJ1rb/wNAMk4xqQJZdoyAFQxoizRvCRS4ooiQoHUd1hbgtE4 shXJ/b/3BuxjX9DQ== To: =?utf-8?b?QW5kcsOp?= Pribil , "linux-rt-users@vger.kernel.org" Subject: [PATCH] printk/console: Enable console kthreads only when there is no boot console left In-Reply-To: <87bklnro9j.fsf@jogness.linutronix.de> References: <87bklnro9j.fsf@jogness.linutronix.de> Date: Tue, 21 Feb 2023 17:21:08 +0106 Message-ID: <878rgrro4z.fsf@jogness.linutronix.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org The console kthreads uncovered several races in console drivers. All problems were in situation when a console was being properly initialized and registered while an early console, using the same port, was being used. These problems are pretty hard to debug because they often result into silent boot crashes. It would be nice to fix them but it looks like a can of worms. Prevent these problems by delaying the use of console kthreads after all early consoles are gone. It might later be optimized. But let's close this can of worms with a big hammer for now so that they do not break first impression on the kthreads that solve other real problems. Link: https://lore.kernel.org/r/20220619204949.50d9154d@thinkpad Link: https://lore.kernel.org/r/2a82eae7-a256-f70c-fd82-4e510750906e@samsung.com Reported-by: Marek Behún Signed-off-by: Petr Mladek Tested-by: Marek Behún [ rebased for 5.10.165-rt81 by john.ogness ] --- kernel/printk/printk.c | 31 ++++++++++++++++++++++++++----- 1 file changed, 26 insertions(+), 5 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index d2205872304d..db095bd0f17c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2986,6 +2986,21 @@ void __init console_init(void) } } +#ifdef CONFIG_PRINTK +static int __init printk_activate_kthreads(void) +{ + struct console *con; + + console_lock(); + for_each_console(con) + printk_start_kthread(con); + kthreads_started = true; + console_unlock(); + + return 0; +} +#endif + /* * Some boot consoles access data that is in the init section and which will * be discarded after the initcalls have been run. To make sure that no code @@ -3002,6 +3017,7 @@ void __init console_init(void) */ static int __init printk_late_init(void) { + bool no_bootcon = true; struct console *con; int ret; @@ -3023,15 +3039,20 @@ static int __init printk_late_init(void) pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n", con->name, con->index); unregister_console(con); + continue; } + + no_bootcon = false; } #ifdef CONFIG_PRINTK - console_lock(); - for_each_console(con) - start_printk_kthread(con); - kthreads_started = true; - console_unlock(); + /* + * Some console drivers are not ready to use the same port with + * boot (early) and normal console in parallel. Stay on the safe + * side and enable kthreads only when there is no boot console. + */ + if (no_bootcon) + printk_activate_kthreads(); #endif ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,