From nobody Wed Sep 10 02:48:46 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 18CE4C0015E for ; Fri, 28 Jul 2023 00:03:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232030AbjG1ADI (ORCPT ); Thu, 27 Jul 2023 20:03:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46688 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231570AbjG1ACp (ORCPT ); Thu, 27 Jul 2023 20:02:45 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 006B1BF for ; Thu, 27 Jul 2023 17:02:42 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1690502558; 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=+2Y16kupdutHjhiUaBB096BqHV4UeSVGmrxKDvfMgWs=; b=sgipofk7vGitPK8JkqZ6tuBbrENDClmWXVbTPa43JXKL3wJBb8zRCefBwj83Rpnr0D2mnC +ofWrSWlqWlAI1cVj8QU4hIKCjX03YfIvvjFM/yUMotvcn+BurtrxepWdzN+LUSAbLRDMG wk8TQrh/awtK438uUGWAoxIBSZwYJK6hSnwevk9Im/3DTk76wAWIYUhyUDIkTBT2bmcTRX LocX8AJqRFLO9OikS8e4x/tXumI08M4VdnZ/j4pfdRq7As6pHbgtHJYnKgwSKLvs+xCTCP dWYsmiwtojGS/DfX63DdYDcSW5pTsW6I0z7SvFrsq3Kk48SlDAkFMKqx2BAERw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1690502558; 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=+2Y16kupdutHjhiUaBB096BqHV4UeSVGmrxKDvfMgWs=; b=Ui+XH/mSQ/PmaAfWhLql0P8DmP9eOR63WLUKjroDBUypMeaYhfvNbbqwul4r/A6hNb61hB 5pbHj2pM091ZISDw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v2 7/8] printk: nbcon: Add emit function and callback function for atomic printing Date: Fri, 28 Jul 2023 02:08:32 +0206 Message-Id: <20230728000233.50887-8-john.ogness@linutronix.de> In-Reply-To: <20230728000233.50887-1-john.ogness@linutronix.de> References: <20230728000233.50887-1-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) --- include/linux/console.h | 27 ++++++++ kernel/printk/internal.h | 6 ++ kernel/printk/printk.c | 9 +-- kernel/printk/printk_nbcon.c | 121 ++++++++++++++++++++++++++++++++++- 4 files changed, 156 insertions(+), 7 deletions(-) diff --git a/include/linux/console.h b/include/linux/console.h index a50eaa3b8420..3d129b2b70a1 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -243,6 +243,7 @@ struct printk_buffers; * @unsafe: This context is in an unsafe section * @hostile: Acquire console by hostile takeover * @takeover_unsafe: Acquire console by hostile takeover even if unsafe + * @backlog: Ringbuffer has pending records * @pbufs: Pointer to the text buffer for this context * @seq: The sequence number to print for this context */ @@ -255,11 +256,28 @@ struct nbcon_context { unsigned int hostile : 1; unsigned int takeover_unsafe : 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 + * @hostile_unsafe: The @unsafe value before a hostile takeover + */ +struct nbcon_write_context { + struct nbcon_context __private ctxt; + char *outbuf; + unsigned int len; + bool hostile_unsafe; +}; + /** * struct console - The console descriptor structure * @name: The name of the console driver @@ -280,6 +298,7 @@ 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 @@ -304,6 +323,8 @@ 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; @@ -433,6 +454,12 @@ 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); +#else +static inline bool nbcon_can_proceed(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/internal.h b/kernel/printk/internal.h index 1baccddf83b8..96dcb2cc05b1 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -128,3 +128,9 @@ 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/printk.c b/kernel/printk/printk.c index 64e404aacbc4..0124c433da9d 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -716,9 +716,6 @@ 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; @@ -2751,7 +2748,7 @@ 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); @@ -2805,8 +2802,8 @@ 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 diff --git a/kernel/printk/printk_nbcon.c b/kernel/printk/printk_nbcon.c index e41f2eff5ef6..e1f0e4278ffa 100644 --- a/kernel/printk/printk_nbcon.c +++ b/kernel/printk/printk_nbcon.c @@ -198,7 +198,6 @@ void nbcon_seq_force(struct console *con, u64 seq) * In case of fail the console has been likely taken over. However, the * caller must still assume it has ownership and decide how to proceed. */ -__maybe_unused static bool nbcon_seq_try_update(struct nbcon_context *ctxt) { struct console *con =3D ctxt->console; @@ -717,6 +716,33 @@ 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 the state is correct. False if ownership was + * handed over or taken. + * + * Must be invoked after the record was dumped into the assigned buffer + * and at appropriate safe places in the driver. + * + * When this function returns false then the calling context is no longer + * the owner 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); + /** * nbcon_context_update_unsafe - Update the unsafe bit in @con->nbcon_state * @ctxt: The nbcon context from nbcon_context_try_acquire() @@ -761,6 +787,99 @@ static bool nbcon_context_update_unsafe(struct nbcon_c= ontext *ctxt, bool unsafe) return true; } =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 the state is correct. False if ownership was + * handed over or taken. + * + * When this function returns false then the calling context is no longer + * the owner 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; + + ctxt->backlog =3D printk_get_next_message(&pmsg, ctxt->seq, is_extended, = true); + if (!ctxt->backlog) + return true; + + /* + * @con->dropped is not protected in case of hostile takeovers. 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); + + /* Safety point. Do not touch state in case of takeover. */ + nbcon_state_read(con, &cur); + if (!nbcon_context_can_proceed(ctxt, &cur)) + return false; + + /* For skipped records just update seq/dropped in @con. */ + if (pmsg.outbuf_len =3D=3D 0) + goto update_con; + + /* Set the write context before calling write callback. */ + wctxt->hostile_unsafe =3D cur.hostile_unsafe; + wctxt->len =3D pmsg.outbuf_len; + if (wctxt->len) + wctxt->outbuf =3D &pmsg.pbufs->outbuf[0]; + else + wctxt->outbuf =3D NULL; + + 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: + if (dropped !=3D con_dropped) { + /* Counterpart to the READ_ONCE() above. */ + WRITE_ONCE(con->dropped, dropped); + } + + ctxt->seq =3D pmsg.seq + 1; + if (!nbcon_seq_try_update(ctxt)) { + /* This context probably lost ownership. Check. */ + return nbcon_can_proceed(wctxt); + } + + return true; +} + /** * nbcon_init - Initialize the nbcon console specific data * @con: Console to initialize --=20 2.39.2