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 3D3B1EEB57E for ; Sat, 9 Sep 2023 01:14:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346312AbjIIBO2 (ORCPT ); Fri, 8 Sep 2023 21:14:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43272 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345894AbjIIBOY (ORCPT ); Fri, 8 Sep 2023 21:14:24 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 784F12694; Fri, 8 Sep 2023 18:14:02 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB8D9C116A7; Sat, 9 Sep 2023 01:13:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1694221999; bh=kg4R1h/fNOZV0D2244wKfNAhBav9HmO2lNH3eR6n1QA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jI1zVrNJvk2jVkfkyAvvyDxd0gPekdcHJen7W9IqFUmoaFlY6snugkJ+lRf4LUUW9 Sh7bQ8ndAKmnoiOWDvYtzKyImJ4xmdXhPviOJD2d52D8KN7wjqtfoqKduNXM9ElkUo Y0D9YxiZ6aE6D3JWYl4g8BjuaDJlPeL0T9NOI1pUD4j2NdsMNl79eY46p77UcqOKjN QCx3uRZsIbh8L2uGXZEj4zB8uNECDyUwL28CW3WDQnWJms0UZ4SCY804ZdwoICncUw t0YzN4RoigRUbXLz4Jmsk82GmzG32nQg1YU5e9K3PfLTeItJxz1lvrpQTd3hLXivmH 0QbBi4veIu/8w== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: John Ogness , Sergey Senozhatsky , Petr Mladek , Sasha Levin Subject: [PATCH AUTOSEL 6.1 2/3] printk: Consolidate console deferred printing Date: Fri, 8 Sep 2023 21:13:13 -0400 Message-Id: <20230909011314.3581953-2-sashal@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230909011314.3581953-1-sashal@kernel.org> References: <20230909011314.3581953-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.1.52 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: John Ogness [ Upstream commit 696ffaf50e1f8dbc66223ff614473f945f5fb8d8 ] Printing to consoles can be deferred for several reasons: - explicitly with printk_deferred() - printk() in NMI context - recursive printk() calls The current implementation is not consistent. For printk_deferred(), irq work is scheduled twice. For NMI und recursive, panic CPU suppression and caller delays are not properly enforced. Correct these inconsistencies by consolidating the deferred printing code so that vprintk_deferred() is the top-level function for deferred printing and vprintk_emit() will perform whichever irq_work queueing is appropriate. Also add kerneldoc for wake_up_klogd() and defer_console_output() to clarify their differences and appropriate usage. Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230717194607.145135-6-john.ogness@linutronix.de Signed-off-by: Sasha Levin --- kernel/printk/printk.c | 35 ++++++++++++++++++++++++++++------- kernel/printk/printk_safe.c | 9 ++------- 2 files changed, 30 insertions(+), 14 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 4b9429f3fd6d8..cc53fb77f77cc 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2269,7 +2269,11 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } - wake_up_klogd(); + if (in_sched) + defer_console_output(); + else + wake_up_klogd(); + return printed_len; } EXPORT_SYMBOL(vprintk_emit); @@ -3490,11 +3494,33 @@ static void __wake_up_klogd(int val) preempt_enable(); } +/** + * wake_up_klogd - Wake kernel logging daemon + * + * Use this function when new records have been added to the ringbuffer + * and the console printing of those records has already occurred or is + * known to be handled by some other context. This function will only + * wake the logging daemon. + * + * Context: Any context. + */ void wake_up_klogd(void) { __wake_up_klogd(PRINTK_PENDING_WAKEUP); } +/** + * defer_console_output - Wake kernel logging daemon and trigger + * console printing in a deferred context + * + * Use this function when new records have been added to the ringbuffer, + * this context is responsible for console printing those records, but + * the current context is not allowed to perform the console printing. + * Trigger an irq_work context to perform the console printing. This + * function also wakes the logging daemon. + * + * Context: Any context. + */ void defer_console_output(void) { /* @@ -3511,12 +3537,7 @@ void printk_trigger_flush(void) int vprintk_deferred(const char *fmt, va_list args) { - int r; - - r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args); - defer_console_output(); - - return r; + return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args); } int _printk_deferred(const char *fmt, ...) diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index ef0f9a2044da1..6d10927a07d83 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -38,13 +38,8 @@ asmlinkage int vprintk(const char *fmt, va_list args) * Use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. */ - if (this_cpu_read(printk_context) || in_nmi()) { - int len; - - len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args); - defer_console_output(); - return len; - } + if (this_cpu_read(printk_context) || in_nmi()) + return vprintk_deferred(fmt, args); /* No obstacles. */ return vprintk_default(fmt, args); -- 2.40.1