From nobody Mon Apr 6 04:44:19 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 CFC33C6FA82 for ; Sat, 10 Sep 2022 22:28:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230274AbiIJW2S (ORCPT ); Sat, 10 Sep 2022 18:28:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45770 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229982AbiIJW1o (ORCPT ); Sat, 10 Sep 2022 18:27:44 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7AE703D5A0 for ; Sat, 10 Sep 2022 15:27:43 -0700 (PDT) Message-ID: <20220910222300.712668210@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1662848861; 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=o5EroeZfB4NRvl63EpSxfqZIvT4RtM7/V27p+d+Wyos=; b=Lq9KRRbRCX0Ak4qz8PNcmnbY1qO4QNuFUisqEyBcaC5V2qUJOYoGBlTG0ZgaRxHg4CRI78 G323bD21b5keHOyH+Je+VPkSF2+aXuajMFh8PlD4ejaIig7y9+BGqkcmuxmUMxLLk/ZJlG JS6hS0K9YILffaYp7z/VAm6Obqb3AkoU73qZcUAiAWbTV1m2enP0INBpikmYVyMVaQezS2 PfYjSVb4htLORkATadQbQAyA2evBdVOlOuDBZBLlSPgMEz2RTZ7fxXbAEbdtjPBSniWcni 9NnwSLKJaRWNi5Gt/y1iGVoJi5hOiwjcbTtph597AlCSKOiKvrVU/Cam5ML3jA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1662848861; 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=o5EroeZfB4NRvl63EpSxfqZIvT4RtM7/V27p+d+Wyos=; b=sYK6VGhDAuF/Gqfwp7U/eUg7y/W1Byds18bfIvK6JOlosn9b09WsD0fVaMKF95jHZnCAym IpH7WSzU4DPAXiAQ== 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 06/29] printk: Protect [un]register_console() with a mutex References: <20220910221947.171557773@linutronix.de> MIME-Version: 1.0 Date: Sun, 11 Sep 2022 00:27:41 +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" Unprotected list walks are a brilliant idea. Especially in the context of hotpluggable consoles. Signed-off-by: Thomas Gleixner --- include/linux/console.h | 30 ++++++++++++++++-- kernel/printk/printk.c | 79 ++++++++++++++++++++++++++++++++++++++++---= ----- 2 files changed, 93 insertions(+), 16 deletions(-) --- a/include/linux/console.h +++ b/include/linux/console.h @@ -157,10 +157,34 @@ struct console { struct console *next; }; =20 -/* - * for_each_console() allows you to iterate on each console +#ifdef CONFIG_LOCKDEP +extern void lockdep_assert_console_list_lock_held(void); +#else +static inline void lockdep_assert_console_list_lock_held(void) { } +#endif + +extern void console_list_lock(void) __acquires(console_mutex); +extern void console_list_unlock(void) __releases(console_mutex); + +/** + * for_each_registered_console() - Iterator over registered consoles + * @con: struct console pointer used as loop cursor + * + * Requires console_list_lock to be held. Can only be invoked from + * preemptible context. + */ +#define for_each_registered_console(con) \ + lockdep_assert_console_list_lock_held(); \ + for (con =3D console_drivers; con !=3D NULL; con =3D con->next) + +/** + * for_each_console() - Iterator over registered consoles + * @con: struct console pointer used as loop cursor + * + * Requires console_lock to be held which guarantees that the + * list is immutable. */ -#define for_each_console(con) \ +#define for_each_console(con) \ for (con =3D console_drivers; con !=3D NULL; con =3D con->next) =20 extern int console_set_on_cmdline; --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -79,10 +79,14 @@ int oops_in_progress; EXPORT_SYMBOL(oops_in_progress); =20 /* - * console_sem protects the console_drivers list, and also - * provides serialisation for access to the entire console - * driver system. + * console_sem protects the console_drivers list, and also provides + * serialization for access to the entire console driver system. + * + * console_mutex serializes register/unregister. console_sem has to be + * taken for any list manipulation inside the console_mutex locked + * section to keep the console BKL machinery happy. */ +static DEFINE_MUTEX(console_mutex); static DEFINE_SEMAPHORE(console_sem); struct console *console_drivers; EXPORT_SYMBOL_GPL(console_drivers); @@ -103,6 +107,12 @@ static int __read_mostly suppress_panic_ static struct lockdep_map console_lock_dep_map =3D { .name =3D "console_lock" }; + +void lockdep_assert_console_list_lock_held(void) +{ + lockdep_assert_held(&console_mutex); +} + #endif =20 enum devkmsg_log_bits { @@ -220,6 +230,26 @@ int devkmsg_sysctl_set_loglvl(struct ctl } #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */ =20 +/** + * console_list_lock - Lock the console list + * + * For non-console related list walks, e.g. procfs, sysfs... + */ +void console_list_lock(void) +{ + mutex_lock(&console_mutex); +} + +/** + * console_list_unlock - Unlock the console list + * + * Counterpart to console_list_lock() + */ +void console_list_unlock(void) +{ + mutex_unlock(&console_mutex); +} + /* * Helper macros to handle lockdep when locking/unlocking console_sem. We = use * macros instead of functions so that _RET_IP_ contains useful informatio= n. @@ -2978,17 +3008,21 @@ struct tty_driver *console_device(int *i void console_stop(struct console *console) { __pr_flush(console, 1000, true); + console_list_lock(); console_lock(); console->flags &=3D ~CON_ENABLED; console_unlock(); + console_list_unlock(); } EXPORT_SYMBOL(console_stop); =20 void console_start(struct console *console) { + console_list_lock(); console_lock(); console->flags |=3D CON_ENABLED; console_unlock(); + console_list_unlock(); __pr_flush(console, 1000, true); } EXPORT_SYMBOL(console_start); @@ -3081,6 +3115,8 @@ static void try_enable_default_console(s (con->flags & CON_BOOT) ? "boot" : "", \ con->name, con->index, ##__VA_ARGS__) =20 +static int console_unregister_locked(struct console *console); + /* * The console driver calls this routine during kernel initialization * to register the console printing procedure with printk() and to @@ -3107,13 +3143,14 @@ void register_console(struct console *ne bool realcon_enabled =3D false; int err; =20 - for_each_console(con) { + console_list_lock(); + for_each_registered_console(con) { if (WARN(con =3D=3D newcon, "console '%s%d' already registered\n", con->name, con->index)) - return; + goto unlock; } =20 - for_each_console(con) { + for_each_registered_console(con) { if (con->flags & CON_BOOT) bootcon_enabled =3D true; else @@ -3124,7 +3161,7 @@ void register_console(struct console *ne if (newcon->flags & CON_BOOT && realcon_enabled) { pr_info("Too late to register bootconsole %s%d\n", newcon->name, newcon->index); - return; + goto unlock; } =20 /* @@ -3155,7 +3192,7 @@ void register_console(struct console *ne =20 /* printk() messages are not printed to the Braille console. */ if (err || newcon->flags & CON_BRL) - return; + goto unlock; =20 /* * If we have a bootconsole, and are switching to a real console, @@ -3209,14 +3246,17 @@ void register_console(struct console *ne if (bootcon_enabled && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) =3D=3D CON_CONSDEV) && !keep_bootcon) { - for_each_console(con) + for_each_console(con) { if (con->flags & CON_BOOT) - unregister_console(con); + console_unregister_locked(con); + } } +unlock: + console_list_unlock(); } EXPORT_SYMBOL(register_console); =20 -int unregister_console(struct console *console) +static int console_unregister_locked(struct console *console) { struct console *con; int res; @@ -3269,6 +3309,16 @@ int unregister_console(struct console *c =20 return res; } + +int unregister_console(struct console *console) +{ + int res; + + console_list_lock(); + res =3D console_unregister_locked(console); + console_list_unlock(); + return res; +} EXPORT_SYMBOL(unregister_console); =20 /* @@ -3320,7 +3370,8 @@ static int __init printk_late_init(void) struct console *con; int ret; =20 - for_each_console(con) { + console_list_lock(); + for_each_registered_console(con) { if (!(con->flags & CON_BOOT)) continue; =20 @@ -3337,9 +3388,11 @@ 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); + console_unregister_locked(con); } } + console_list_unlock(); + ret =3D cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL, console_cpu_notify); WARN_ON(ret < 0);