From nobody Fri Dec 19 03:43:32 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 246E8CD13D1 for ; Sat, 16 Sep 2023 19:21:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239210AbjIPTU7 (ORCPT ); Sat, 16 Sep 2023 15:20:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59680 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235791AbjIPTUY (ORCPT ); Sat, 16 Sep 2023 15:20:24 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 48A45CED for ; Sat, 16 Sep 2023 12:20:18 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1694892015; 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=yvzwbYjYpGtpc5SL3eYC1oLQ+jH59dIYahpYWig24cg=; b=VkbUFqDyZl8/l9mPXvEDjVV+VgN/M6UFDEgWCGl/RQY4mCdPXYwaEcNUiq3phqceQ7kW5Y FVY6cW2Z2FesXBIF+TPqoYKVmxHPG4mBmkT9In8LVLc60vBFWdRUyAcbLd8acooKUpZr9e 9P0cGs69gWKfnTmHge8+tMF7WbKGU7+pKDXe+mHCyGmhOPYPLmtJ1aBKdnCcJZs3ljLN64 m67Iow7k0GhDV6FQnYkw49aE7Fd1x1L6T6Cj5nfdJJM4sohj2a6xy8NDRVK0naNaBwQiVe Q9qnme2TldT5metvCczh3vatIQEH6zNLz+Kvks7ep30GOt08StnohxUiHB8R4A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1694892015; 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=yvzwbYjYpGtpc5SL3eYC1oLQ+jH59dIYahpYWig24cg=; b=+4VZC6DkSp7M5hHDrnM79OpSeQNGG1cmmFZBmqswG5kN+OntG02/H5moO6+Z1MwsWplG+/ Mb+YEkbKbyaZxOCw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v5 8/8] printk: nbcon: Allow drivers to mark unsafe regions and check state Date: Sat, 16 Sep 2023 21:26:07 +0206 Message-Id: <20230916192007.608398-9-john.ogness@linutronix.de> In-Reply-To: <20230916192007.608398-1-john.ogness@linutronix.de> References: <20230916192007.608398-1-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 For the write_atomic callback, the console driver may have unsafe regions that need to be appropriately marked. Provide functions that accept the nbcon_write_context struct to allow for the driver to enter and exit unsafe regions. Also provide a function for drivers to check if they are still the owner of the console. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Reviewed-by: Petr Mladek --- include/linux/console.h | 10 ++++++ kernel/printk/nbcon.c | 75 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 85 insertions(+) diff --git a/include/linux/console.h b/include/linux/console.h index 14563dcb34b1..e4fc6f7c1496 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -451,6 +451,16 @@ static inline bool console_is_registered(const struct = console *con) lockdep_assert_console_list_lock_held(); \ hlist_for_each_entry(con, &console_list, node) =20 +#ifdef CONFIG_PRINTK +extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); +extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); +extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); +#else +static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { = return false; } +static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) {= return false; } +static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { = return false; } +#endif + extern int console_set_on_cmdline; extern struct console *early_console; =20 diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index 6e05d263fd22..b96077152f49 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -732,6 +732,41 @@ static bool nbcon_context_can_proceed(struct nbcon_con= text *ctxt, struct nbcon_s return false; } =20 +/** + * nbcon_can_proceed - Check whether ownership can proceed + * @wctxt: The write context that was handed to the write function + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. + * + * It is used in nbcon_enter_unsafe() to make sure that it still owns the + * lock. Also it is used in nbcon_exit_unsafe() to eventually free the lock + * for a higher priority context which asked for the friendly handover. + * + * It can be called inside an unsafe section when the console is just + * temporary in safe state instead of exiting and entering the unsafe stat= e. + * + * Also it can be called in the safe context before doing an expensive safe + * operation. It does not make sense to do the operation when a higher + * priority context took the lock. + * + * When this function returns false then the calling context no longer owns + * the console and is no longer allowed to go forward. In this case it must + * back out immediately and carefully. The buffer content is also no longer + * trusted since it no longer belongs to the calling context. + */ +bool nbcon_can_proceed(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con =3D ctxt->console; + struct nbcon_state cur; + + nbcon_state_read(con, &cur); + + return nbcon_context_can_proceed(ctxt, &cur); +} +EXPORT_SYMBOL_GPL(nbcon_can_proceed); + #define nbcon_context_enter_unsafe(c) __nbcon_context_update_unsafe(c, tru= e) #define nbcon_context_exit_unsafe(c) __nbcon_context_update_unsafe(c, fals= e) =20 @@ -782,6 +817,46 @@ static bool __nbcon_context_update_unsafe(struct nbcon= _context *ctxt, bool unsaf return nbcon_context_can_proceed(ctxt, &cur); } =20 +/** + * nbcon_enter_unsafe - Enter an unsafe region in the driver + * @wctxt: The write context that was handed to the write function + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. + * + * When this function returns false then the calling context no longer owns + * the console and is no longer allowed to go forward. In this case it must + * back out immediately and carefully. The buffer content is also no longer + * trusted since it no longer belongs to the calling context. + */ +bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + + return nbcon_context_enter_unsafe(ctxt); +} +EXPORT_SYMBOL_GPL(nbcon_enter_unsafe); + +/** + * nbcon_exit_unsafe - Exit an unsafe region in the driver + * @wctxt: The write context that was handed to the write function + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. + * + * When this function returns false then the calling context no longer owns + * the console and is no longer allowed to go forward. In this case it must + * back out immediately and carefully. The buffer content is also no longer + * trusted since it no longer belongs to the calling context. + */ +bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + + return nbcon_context_exit_unsafe(ctxt); +} +EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); + /** * nbcon_emit_next_record - Emit a record in the acquired context * @wctxt: The write context that will be handed to the write function --=20 2.39.2