From nobody Mon Feb 9 07:20:35 2026 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 71CF7EB64DC for ; Mon, 10 Jul 2023 13:45:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233025AbjGJNph (ORCPT ); Mon, 10 Jul 2023 09:45:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231382AbjGJNpb (ORCPT ); Mon, 10 Jul 2023 09:45:31 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9CEF3FE for ; Mon, 10 Jul 2023 06:45:29 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1688996728; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gNoZRjtYvz+muzS7qSrxZkmQzTEAXcTSx4NPxxauFRc=; b=dmXuNtNql6F9emsQAi7+TV8RVDFsgs/MSWxH3vWrxR75nEc4ecMk3zgTO2CrhNzZEuwxeY 4xLtw9hxiqEjuxvOoNKLHl8ni1PIqh+tOv8g26LLOXl3CvkNk2KIZb0tBVfICSxz6TXR0I +xChvwdiuLZ8QGO+8VsCk7NbpB/YWqPhosAcBQlM8Z4Qojn40eIjiuUzz1dudqj39JEz2t q4npg8Scp2qOU+3tu24rQhIcOUP1B3ZG5Ldu+O3A1l5VfAr1qeQs104Gjsh4rh0o30htIk rnazfhrVUD2rQUgZrk1eYtFgRK8/VKp6tNC1GHduecHy/TOjqVSqWZeh6EFTmg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1688996728; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gNoZRjtYvz+muzS7qSrxZkmQzTEAXcTSx4NPxxauFRc=; b=MkXNNujyGh+shQ0/nLVDn/7Uxr5/7KEvPHgmKG2qVky0opg0FfV/QtypgOp4ZX6npSJzKH vacKBcLg34H2F7Cw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v2 3/5] printk: Consolidate console deferred printing Date: Mon, 10 Jul 2023 15:51:22 +0206 Message-Id: <20230710134524.25232-4-john.ogness@linutronix.de> In-Reply-To: <20230710134524.25232-1-john.ogness@linutronix.de> References: <20230710134524.25232-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 --- 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 8a6c917dc081..e7632ed3b6fd 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2306,7 +2306,11 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } =20 - wake_up_klogd(); + if (in_sched) + defer_console_output(); + else + wake_up_klogd(); + return printed_len; } EXPORT_SYMBOL(vprintk_emit); @@ -3817,11 +3821,33 @@ static void __wake_up_klogd(int val) preempt_enable(); } =20 +/** + * 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); } =20 +/** + * 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) { /* @@ -3838,12 +3864,7 @@ void printk_trigger_flush(void) =20 int vprintk_deferred(const char *fmt, va_list args) { - int r; - - r =3D vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args); - defer_console_output(); - - return r; + return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args); } =20 int _printk_deferred(const char *fmt, ...) diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index ef0f9a2044da..6d10927a07d8 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 =3D 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); =20 /* No obstacles. */ return vprintk_default(fmt, args); --=20 2.30.2