From nobody Mon Apr 6 04:44:18 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 52EB6C6FA82 for ; Sat, 10 Sep 2022 22:29:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230212AbiIJW3T (ORCPT ); Sat, 10 Sep 2022 18:29:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230314AbiIJW2a (ORCPT ); Sat, 10 Sep 2022 18:28:30 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 61E5F43333 for ; Sat, 10 Sep 2022 15:28:02 -0700 (PDT) Message-ID: <20220910222301.422514421@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1662848880; 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: references:references; bh=GORp14X0ZPsta6IucVBlmsXp9iduDN+zPIQ5DiLrn3I=; b=iMQNCn8ruP6Jx1Gh4WzWgOGiyi+3IGoUmLYw4P1Z5niRDBN4m60017dC1LeiV8lbh9N6pS V6I1RzY3iRGq/U/UwagFgVk+SI3pYhLPRkmVl3qkBrofWfVG63ydgghR1Qw1WM5CXfawxh MkN/CUdMlVmbnadOJz7UyEbHE6ZkmQLCFGO8lQ0AG0GrgRCe2mySkHFHn5z0Y5MMLBwgEn b/gIGoP5Zte0QjN0jSN0tzgzsx/PHMY61suwONVe7uRehoIK2i7YRNHwwjP4VTtmDd0lfE W/Q3hy8YqoLrtzvehknIHVpvx8YqD0yR9oiRVEdniup4gNeQuCGvzq51ijuLdw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1662848880; 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: references:references; bh=GORp14X0ZPsta6IucVBlmsXp9iduDN+zPIQ5DiLrn3I=; b=59bMwLuHY15oRwAWgcslNBmblSP4msdmhJTJnuUN6FzYZmokzKg6IUwUuaL4qA/e+i8XcH R9XwkH0jsSjGhABA== From: Thomas Gleixner To: LKML Cc: John Ogness , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Peter Zijlstra , "Paul E. McKenney" , Daniel Vetter , Greg Kroah-Hartman , Helge Deller , Jason Wessel , Daniel Thompson Subject: [patch RFC 18/29] printk: Handle dropped message smarter References: <20220910221947.171557773@linutronix.de> MIME-Version: 1.0 Date: Sun, 11 Sep 2022 00:27:59 +0200 (CEST) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" No need for an extra buffer type. Regular formatting which needs the '$N messages dropped' printout can sprintf() it into the unused extended text buffer. As a further simplification move the 'dropped' message right in front of the actual record text and let the write function output it in one go. Signed-off-by: Thomas Gleixner --- include/linux/console.h | 12 ++---- kernel/printk/printk.c | 86 +++++++++++++++++++++++++++++++------------= ----- 2 files changed, 61 insertions(+), 37 deletions(-) --- a/include/linux/console.h +++ b/include/linux/console.h @@ -175,28 +175,26 @@ enum cons_flags { /** * struct cons_text_buf - console output text buffer * @ext_text: Buffer for extended log format text - * @dropped_text: Buffer for dropped text * @text: Buffer for ringbuffer text */ struct cons_text_buf { - union { - char ext_text[CONSOLE_EXT_LOG_MAX]; - char dropped_text[DROPPED_TEXT_MAX]; - }; - char text[CONSOLE_LOG_MAX]; -}; + char ext_text[CONSOLE_EXT_LOG_MAX]; + char text[CONSOLE_LOG_MAX]; +} __no_randomize_layout; =20 /** * struct cons_outbuf_desc - console output buffer descriptor * @txtbuf: Pointer to buffer for storing the text * @outbuf: Pointer to the position in @buffer for * writing it out to the device + * @dropped: The dropped count * @len: Message length * @extmsg: Select extended format printing */ struct cons_outbuf_desc { struct cons_text_buf *txtbuf; char *outbuf; + unsigned long dropped; unsigned int len; bool extmsg; }; --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1957,27 +1957,6 @@ static int console_trylock_spinning(void } =20 /* - * Call the specified console driver, asking it to write out the specified - * text and length. If @dropped_text is non-NULL and any records have been - * dropped, a dropped message will be written out first. - */ -static void call_console_driver(struct console *con, const char *text, siz= e_t len, - char *dropped_text) -{ - size_t dropped_len; - - if (con->dropped && dropped_text) { - dropped_len =3D snprintf(dropped_text, DROPPED_TEXT_MAX, - "** %lu printk messages dropped **\n", - con->dropped); - con->dropped =3D 0; - con->write(con, dropped_text, dropped_len); - } - - con->write(con, text, len); -} - -/* * Recursion is tracked separately on each CPU. If NMIs are supported, an * additional NMI context per CPU is also separately tracked. Until per-CPU * is available, a separate "early tracking" is performed. @@ -2356,10 +2335,6 @@ static ssize_t msg_print_ext_body(char * struct dev_printk_info *dev_info) { return 0; } static void console_lock_spinning_enable(void) { } static int console_lock_spinning_disable_and_check(void) { return 0; } -static void call_console_driver(struct console *con, const char *text, siz= e_t len, - char *dropped_text) -{ -} static bool suppress_message_printing(int level) { return false; } static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true= ; } static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_= progress) { return true; } @@ -2684,6 +2659,46 @@ static void __console_unlock(void) up_console_sem(); } =20 +/** + * cons_print_dropped - Print 'dropped' message if required + * @desc: Pointer to the output descriptor + * + * Prints the 'dropped' message info the output buffer if @desc->dropped is + * not 0 and the regular format is requested. Extended format does not + * need this message because it prints the sequence numbers. + * + * In regular format the extended message buffer is not in use. + * So print into it at the beginning and move the resulting string + * just in front of the regular text buffer so that the message can + * be printed in one go. + * + * In case of a message this returns with @desc->outbuf and @desc->len + * updated. If no message is required then @desc is not modified. + */ +static void cons_print_dropped(struct cons_outbuf_desc *desc) +{ + struct cons_text_buf *txtbuf =3D desc->txtbuf; + size_t len; + + if (!desc->dropped || desc->extmsg) + return; + + if (WARN_ON_ONCE(desc->outbuf !=3D txtbuf->text)) + return; + + /* Print it into ext_text which is unused */ + len =3D snprintf(txtbuf->ext_text, DROPPED_TEXT_MAX, + "** %lu printk messages dropped **\n", desc->dropped); + desc->dropped =3D 0; + + /* Copy it just below text so it goes out with one write */ + memcpy(txtbuf->text - len, txtbuf->ext_text, len); + + /* Update the descriptor */ + desc->len +=3D len; + desc->outbuf -=3D len; +} + =20 /** * cons_fill_outbuf - Fill the output buffer with the next record @@ -2737,17 +2752,26 @@ static bool cons_fill_outbuf(struct cons } =20 if (desc->extmsg) { + /* + * Extended messages do not require "dropped" message + * as that can be seen from the sequence number + */ write_text =3D txtbuf->ext_text; len =3D info_print_ext_header(write_text, CONSOLE_EXT_LOG_MAX, r.info); len +=3D msg_print_ext_body(write_text + len, CONSOLE_EXT_LOG_MAX - len, &r.text_buf[0], r.info->text_len, &r.info->dev_info); + desc->len =3D len; + desc->outbuf =3D write_text; } else { - write_text =3D txtbuf->text; len =3D record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, pr= intk_time); + + desc->len =3D len; + desc->outbuf =3D txtbuf->text; + desc->dropped =3D con->dropped; + cons_print_dropped(desc); + con->dropped =3D desc->dropped; } =20 - desc->len =3D len; - desc->outbuf =3D write_text; return true; } =20 @@ -2800,8 +2824,10 @@ static bool console_emit_next_record(str printk_safe_enter_irqsave(flags); console_lock_spinning_enable(); =20 - stop_critical_timings(); /* don't trace print latency */ - call_console_driver(con, desc.outbuf, desc.len, extmsg ? NULL : txtbuf->d= ropped_text); + /* don't trace print latency */ + stop_critical_timings(); + /* Write everything out to the hardware */ + con->write(con, desc.outbuf, desc.len); start_critical_timings(); =20 con->seq++;