From nobody Fri Dec 19 04:01:59 2025 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 6EE79EEB560 for ; Fri, 8 Sep 2023 18:51:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243399AbjIHSv5 (ORCPT ); Fri, 8 Sep 2023 14:51:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57488 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241747AbjIHSvz (ORCPT ); Fri, 8 Sep 2023 14:51:55 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F49B1BC1 for ; Fri, 8 Sep 2023 11:51:18 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1694199011; 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=cBog/17jG1mTArwU5kOIIQv+uQFxg8laxa+tevZYKXU=; b=RijY906TtiQUrkrUSSEkXYk3v0DEgFmGmwsJNiylvtABHHs6nzzmlZJTA0A8PnTreDksHJ HB8lzBQc2cA4ElCtz80bMCAbRUDaI6BsCqGeC6BYKau8nEaMIQNtweK6vQ1T+OfjKIIoe4 yv/IuiJ/kvhqLhcihqdknt1/2+4nDcqdHoZHhqsyfe+GeAj5/goWFNb0RHK2ujpZUQq053 DSqSqLRSnrn/LZlw3iCxCWKBciQZT53JwqMTpjwN0w5cOra25OlbkyzTkYsL5eqGp1Mb1s UtnLjX6hfohf+QSgkq7BoRzp9ib3rfg7yY3cwlkRRBpVJc3ZN07sGb32ps8yTg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1694199011; 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=cBog/17jG1mTArwU5kOIIQv+uQFxg8laxa+tevZYKXU=; b=FP0ziImASuXGnDdmQ5oBsds9eXFeeq1dtsD+aOspXmpHxkvyBxj+fsBk+hNMPeAAzFPBXX BjXmEpKq7UrxNcAw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v4 1/8] printk: Add non-BKL (nbcon) console basic infrastructure Date: Fri, 8 Sep 2023 20:56:01 +0206 Message-Id: <20230908185008.468566-2-john.ogness@linutronix.de> In-Reply-To: <20230908185008.468566-1-john.ogness@linutronix.de> References: <20230908185008.468566-1-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" From: Thomas Gleixner The current console/printk subsystem is protected by a Big Kernel Lock, (aka console_lock) which has ill defined semantics and is more or less stateless. This puts severe limitations on the console subsystem and makes forced takeover and output in emergency and panic situations a fragile endeavour that is based on try and pray. The goal of non-BKL (nbcon) consoles is to break out of the console lock jail and to provide a new infrastructure that avoids the pitfalls and also allows console drivers to be gradually converted over. The proposed infrastructure aims for the following properties: - Per console locking instead of global locking - Per console state that allows to make informed decisions - Stateful handover and takeover As a first step, state is added to struct console. The per console state is an atomic_t using a 32bit bit field. Reserve state bits, which will be populated later in the series. Wire it up into the console register/unregister functionality. It was decided to use a bitfield because using a plain u32 with mask/shift operations resulted in uncomprehensible code. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Reviewed-by: Petr Mladek --- include/linux/console.h | 31 ++++++++++++++++++ kernel/printk/Makefile | 2 +- kernel/printk/internal.h | 8 +++++ kernel/printk/nbcon.c | 70 ++++++++++++++++++++++++++++++++++++++++ kernel/printk/printk.c | 13 ++++++-- 5 files changed, 120 insertions(+), 4 deletions(-) create mode 100644 kernel/printk/nbcon.c diff --git a/include/linux/console.h b/include/linux/console.h index 7de11c763eb3..a2d37a7a98a8 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -156,6 +156,8 @@ static inline int con_debug_leave(void) * /dev/kmesg which requires a larger output buffer. * @CON_SUSPENDED: Indicates if a console is suspended. If true, the * printing callbacks must not be called. + * @CON_NBCON: Console can operate outside of the legacy style console_lo= ck + * constraints. */ enum cons_flags { CON_PRINTBUFFER =3D BIT(0), @@ -166,8 +168,32 @@ enum cons_flags { CON_BRL =3D BIT(5), CON_EXTENDED =3D BIT(6), CON_SUSPENDED =3D BIT(7), + CON_NBCON =3D BIT(8), }; =20 +/** + * struct nbcon_state - console state for nbcon consoles + * @atom: Compound of the state fields for atomic operations + * + * To be used for reading and preparing of the value stored in the nbcon + * state variable @console::nbcon_state. + */ +struct nbcon_state { + union { + unsigned int atom; + struct { + }; + }; +}; + +/* + * The nbcon_state struct is used to easily create and interpret values th= at + * are stored in the @console::nbcon_state variable. Ensure this struct st= ays + * within the size boundaries of the atomic variable's underlying type in + * order to avoid any accidental truncation. + */ +static_assert(sizeof(struct nbcon_state) <=3D sizeof(int)); + /** * struct console - The console descriptor structure * @name: The name of the console driver @@ -187,6 +213,8 @@ enum cons_flags { * @dropped: Number of unreported dropped ringbuffer records * @data: Driver private data * @node: hlist node for the console list + * + * @nbcon_state: State for nbcon consoles */ struct console { char name[16]; @@ -206,6 +234,9 @@ struct console { unsigned long dropped; void *data; struct hlist_node node; + + /* nbcon console specific members */ + atomic_t __private nbcon_state; }; =20 #ifdef CONFIG_LOCKDEP diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile index f5b388e810b9..39a2b61c7232 100644 --- a/kernel/printk/Makefile +++ b/kernel/printk/Makefile @@ -1,6 +1,6 @@ # SPDX-License-Identifier: GPL-2.0-only obj-y =3D printk.o -obj-$(CONFIG_PRINTK) +=3D printk_safe.o +obj-$(CONFIG_PRINTK) +=3D printk_safe.o nbcon.o obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) +=3D braille.o obj-$(CONFIG_PRINTK_INDEX) +=3D index.o =20 diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 7d4979d5c3ce..2ca0ab78802c 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -3,6 +3,7 @@ * internal.h - printk internal definitions */ #include +#include =20 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL) void __init printk_sysctl_init(void); @@ -61,6 +62,10 @@ void defer_console_output(void); =20 u16 printk_parse_prefix(const char *text, int *level, enum printk_info_flags *flags); + +void nbcon_init(struct console *con); +void nbcon_cleanup(struct console *con); + #else =20 #define PRINTK_PREFIX_MAX 0 @@ -76,6 +81,9 @@ u16 printk_parse_prefix(const char *text, int *level, #define printk_safe_exit_irqrestore(flags) local_irq_restore(flags) =20 static inline bool printk_percpu_data_ready(void) { return false; } +static inline void nbcon_init(struct console *con) { } +static inline void nbcon_cleanup(struct console *con) { } + #endif /* CONFIG_PRINTK */ =20 /** diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c new file mode 100644 index 000000000000..10266d3e7883 --- /dev/null +++ b/kernel/printk/nbcon.c @@ -0,0 +1,70 @@ +// SPDX-License-Identifier: GPL-2.0-only +// Copyright (C) 2022 Linutronix GmbH, John Ogness +// Copyright (C) 2022 Intel, Thomas Gleixner + +#include +#include +#include "internal.h" +/* + * Printk console printing implementation for consoles that do not depend = on + * the legacy style console_lock mechanism. + */ + +/** + * nbcon_state_set - Helper function to set the console state + * @con: Console to update + * @new: The new state to write + * + * Only to be used when the console is not yet or no longer visible in the + * system. Otherwise use nbcon_state_try_cmpxchg(). + */ +static inline void nbcon_state_set(struct console *con, struct nbcon_state= *new) +{ + atomic_set(&ACCESS_PRIVATE(con, nbcon_state), new->atom); +} + +/** + * nbcon_state_read - Helper function to read the console state + * @con: Console to read + * @state: The state to store the result + */ +static inline void nbcon_state_read(struct console *con, struct nbcon_stat= e *state) +{ + state->atom =3D atomic_read(&ACCESS_PRIVATE(con, nbcon_state)); +} + +/** + * nbcon_state_try_cmpxchg() - Helper function for atomic_try_cmpxchg() on= console state + * @con: Console to update + * @cur: Old/expected state + * @new: New state + * + * Return: True on success. False on fail and @cur is updated. + */ +static inline bool nbcon_state_try_cmpxchg(struct console *con, struct nbc= on_state *cur, + struct nbcon_state *new) +{ + return atomic_try_cmpxchg(&ACCESS_PRIVATE(con, nbcon_state), &cur->atom, = new->atom); +} + +/** + * nbcon_init - Initialize the nbcon console specific data + * @con: Console to initialize + */ +void nbcon_init(struct console *con) +{ + struct nbcon_state state =3D { }; + + nbcon_state_set(con, &state); +} + +/** + * nbcon_cleanup - Cleanup the nbcon console specific data + * @con: Console to cleanup + */ +void nbcon_cleanup(struct console *con) +{ + struct nbcon_state state =3D { }; + + nbcon_state_set(con, &state); +} diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8787d3a72114..c0246093ea41 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3324,9 +3324,10 @@ static void try_enable_default_console(struct consol= e *newcon) newcon->flags |=3D CON_CONSDEV; } =20 -#define con_printk(lvl, con, fmt, ...) \ - printk(lvl pr_fmt("%sconsole [%s%d] " fmt), \ - (con->flags & CON_BOOT) ? "boot" : "", \ +#define con_printk(lvl, con, fmt, ...) \ + printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \ + (con->flags & CON_NBCON) ? "" : "legacy ", \ + (con->flags & CON_BOOT) ? "boot" : "", \ con->name, con->index, ##__VA_ARGS__) =20 static void console_init_seq(struct console *newcon, bool bootcon_register= ed) @@ -3486,6 +3487,9 @@ void register_console(struct console *newcon) newcon->dropped =3D 0; console_init_seq(newcon, bootcon_registered); =20 + if (newcon->flags & CON_NBCON) + nbcon_init(newcon); + /* * Put this console in the list - keep the * preferred driver at the head of the list. @@ -3577,6 +3581,9 @@ static int unregister_console_locked(struct console *= console) */ synchronize_srcu(&console_srcu); =20 + if (console->flags & CON_NBCON) + nbcon_cleanup(console); + console_sysfs_notify(); =20 if (console->exit) --=20 2.39.2