From nobody Fri Dec 19 03:43:33 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 36B54CD13CF for ; Sat, 16 Sep 2023 19:21:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239289AbjIPTVA (ORCPT ); Sat, 16 Sep 2023 15:21:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59666 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235386AbjIPTUY (ORCPT ); Sat, 16 Sep 2023 15:20:24 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45C44CE7 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=8OChr0GSn67JR7FwwS4ZNocQPb8t+7M7snweDbUlbX8=; b=aT8Ylp/DkL4rl4EZbGh+o+g0+2iSZqy0bHXmjjM5jsPNwsETUas5UQIZ0WHxsMEonTvynf lnWB7ItDwCKlT9hHOhUr005/vG/aj9+Qje+5/gMVWeDa7H5evCHt6qpVl+RfauXR+mHdOv RIc32Y95iaYAyMbo9K+DruY7LU0JiYB/XQkYxcLGabtnzQ4CvfiUHDvOXYkwxKC5JHPERI DRDrDWU9i5g15AUkkJ2jX/lxb5eV+XuFFGG2uL8oCHUx2GnHhXdHvcXcqs/zZ/ThAt6qaT m5aBc3Hj9Lu7zE+K7dkWSbCNFJSW+rDrE27ybz9IJdFHlWtyl0mDBF+HHuFnPw== 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=8OChr0GSn67JR7FwwS4ZNocQPb8t+7M7snweDbUlbX8=; b=GueiIGDUlsstqm3XSF4HTQN3M3L1puY78xucWAQqU84DQa/4oLVAR5Jm0FaSLr4BHC2l/M oFr+O7AtjqJgzTCw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v5 7/8] printk: nbcon: Add emit function and callback function for atomic printing Date: Sat, 16 Sep 2023 21:26:06 +0206 Message-Id: <20230916192007.608398-8-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 Implement an emit function for nbcon consoles to output printk messages. It utilizes the lockless printk_get_next_message() and console_prepend_dropped() functions to retrieve/build the output message. The emit function includes the required safety points to check for handover/takeover and calls a new write_atomic callback of the console driver to output the message. It also includes proper handling for updating the nbcon console sequence number. A new nbcon_write_context struct is introduced. This is provided to the write_atomic callback and includes only the information necessary for performing atomic writes. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Reviewed-by: Petr Mladek --- include/linux/console.h | 21 ++++++++ kernel/printk/internal.h | 6 +++ kernel/printk/nbcon.c | 106 ++++++++++++++++++++++++++++++++++++++- kernel/printk/printk.c | 9 ++-- 4 files changed, 134 insertions(+), 8 deletions(-) diff --git a/include/linux/console.h b/include/linux/console.h index 20cd486b76ad..14563dcb34b1 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -242,6 +242,7 @@ struct printk_buffers; * be used only with NBCON_PRIO_PANIC @prio. It * might cause a system freeze when the console * is used later. + * @backlog: Ringbuffer has pending records * @pbufs: Pointer to the text buffer for this context * @seq: The sequence number to print for this context */ @@ -252,11 +253,28 @@ struct nbcon_context { enum nbcon_prio prio; unsigned int allow_unsafe_takeover : 1; =20 + /* members set by emit */ + unsigned int backlog : 1; + /* members set by acquire */ struct printk_buffers *pbufs; u64 seq; }; =20 +/** + * struct nbcon_write_context - Context handed to the nbcon write callbacks + * @ctxt: The core console context + * @outbuf: Pointer to the text buffer for output + * @len: Length to write + * @unsafe_takeover: If a hostile takeover in an unsafe state has occurred + */ +struct nbcon_write_context { + struct nbcon_context __private ctxt; + char *outbuf; + unsigned int len; + bool unsafe_takeover; +}; + /** * struct console - The console descriptor structure * @name: The name of the console driver @@ -277,6 +295,7 @@ struct nbcon_context { * @data: Driver private data * @node: hlist node for the console list * + * @write_atomic: Write callback for atomic context * @nbcon_state: State for nbcon consoles * @nbcon_seq: Sequence number of the next record for nbcon to print * @pbufs: Pointer to nbcon private buffer @@ -301,6 +320,8 @@ struct console { struct hlist_node node; =20 /* nbcon console specific members */ + bool (*write_atomic)(struct console *con, + struct nbcon_write_context *wctxt); atomic_t __private nbcon_state; atomic_long_t __private nbcon_seq; struct printk_buffers *pbufs; diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 6473f5ae4a18..6c2afee5ef62 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -130,3 +130,9 @@ struct printk_message { }; =20 bool other_cpu_in_panic(void); +bool printk_get_next_message(struct printk_message *pmsg, u64 seq, + bool is_extended, bool may_supress); + +#ifdef CONFIG_PRINTK +void console_prepend_dropped(struct printk_message *pmsg, unsigned long dr= opped); +#endif diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index e076096b31c0..6e05d263fd22 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -221,7 +221,6 @@ void nbcon_seq_force(struct console *con, u64 seq) * nbcon_seq_force() was used or the current context no longer owns the * console. In the later case, it will stop printing anyway. */ -__maybe_unused static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq) { unsigned long nbcon_seq =3D __seq_to_nbcon_seq(ctxt->seq); @@ -755,7 +754,6 @@ static bool nbcon_context_can_proceed(struct nbcon_cont= ext *ctxt, struct nbcon_s * * Internal helper to avoid duplicated code. */ -__maybe_unused static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool= unsafe) { struct console *con =3D ctxt->console; @@ -784,6 +782,110 @@ static bool __nbcon_context_update_unsafe(struct nbco= n_context *ctxt, bool unsaf return nbcon_context_can_proceed(ctxt, &cur); } =20 +/** + * nbcon_emit_next_record - Emit a record in the acquired context + * @wctxt: The write context that will be 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. If the caller + * wants to do more it must reacquire the console first. + * + * When true is returned, @wctxt->ctxt.backlog indicates whether there are + * still records pending in the ringbuffer, + */ +__maybe_unused +static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con =3D ctxt->console; + bool is_extended =3D console_srcu_read_flags(con) & CON_EXTENDED; + struct printk_message pmsg =3D { + .pbufs =3D ctxt->pbufs, + }; + unsigned long con_dropped; + struct nbcon_state cur; + unsigned long dropped; + bool done; + + /* + * The printk buffers are filled within an unsafe section. This + * prevents NBCON_PRIO_NORMAL and NBCON_PRIO_EMERGENCY from + * clobbering each other. + */ + + if (!nbcon_context_enter_unsafe(ctxt)) + return false; + + ctxt->backlog =3D printk_get_next_message(&pmsg, ctxt->seq, is_extended, = true); + if (!ctxt->backlog) + return nbcon_context_exit_unsafe(ctxt); + + /* + * @con->dropped is not protected in case of an unsafe hostile + * takeover. In that situation the update can be racy so + * annotate it accordingly. + */ + con_dropped =3D data_race(READ_ONCE(con->dropped)); + + dropped =3D con_dropped + pmsg.dropped; + if (dropped && !is_extended) + console_prepend_dropped(&pmsg, dropped); + + if (!nbcon_context_exit_unsafe(ctxt)) + return false; + + /* For skipped records just update seq/dropped in @con. */ + if (pmsg.outbuf_len =3D=3D 0) + goto update_con; + + /* Initialize the write context for driver callbacks. */ + wctxt->outbuf =3D &pmsg.pbufs->outbuf[0]; + wctxt->len =3D pmsg.outbuf_len; + nbcon_state_read(con, &cur); + wctxt->unsafe_takeover =3D cur.unsafe_takeover; + + if (con->write_atomic) { + done =3D con->write_atomic(con, wctxt); + } else { + nbcon_context_release(ctxt); + WARN_ON_ONCE(1); + done =3D false; + } + + /* If not done, the emit was aborted. */ + if (!done) + return false; + + /* + * Since any dropped message was successfully output, reset the + * dropped count for the console. + */ + dropped =3D 0; +update_con: + /* + * The dropped count and the sequence number are updated within an + * unsafe section. This limits update races to the panic context and + * allows the panic context to win. + */ + + if (!nbcon_context_enter_unsafe(ctxt)) + return false; + + if (dropped !=3D con_dropped) { + /* Counterpart to the READ_ONCE() above. */ + WRITE_ONCE(con->dropped, dropped); + } + + nbcon_seq_try_update(ctxt, pmsg.seq + 1); + + return nbcon_context_exit_unsafe(ctxt); +} + /** * nbcon_alloc - Allocate buffers needed by the nbcon console * @con: Console to allocate buffers for diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 77857d2118ca..778359b21761 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -698,9 +698,6 @@ static ssize_t msg_print_ext_body(char *buf, size_t siz= e, return len; } =20 -static bool printk_get_next_message(struct printk_message *pmsg, u64 seq, - bool is_extended, bool may_supress); - /* /dev/kmsg - userspace message inject/listen interface */ struct devkmsg_user { atomic64_t seq; @@ -2733,7 +2730,7 @@ static void __console_unlock(void) * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated. */ #ifdef CONFIG_PRINTK -static void console_prepend_dropped(struct printk_message *pmsg, unsigned = long dropped) +void console_prepend_dropped(struct printk_message *pmsg, unsigned long dr= opped) { struct printk_buffers *pbufs =3D pmsg->pbufs; const size_t scratchbuf_sz =3D sizeof(pbufs->scratchbuf); @@ -2787,8 +2784,8 @@ static void console_prepend_dropped(struct printk_mes= sage *pmsg, unsigned long d * of @pmsg are valid. (See the documentation of struct printk_message * for information about the @pmsg fields.) */ -static bool printk_get_next_message(struct printk_message *pmsg, u64 seq, - bool is_extended, bool may_suppress) +bool printk_get_next_message(struct printk_message *pmsg, u64 seq, + bool is_extended, bool may_suppress) { static int panic_console_dropped; =20 --=20 2.39.2