From nobody Fri Dec 19 21:49:48 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B6B956F520 for ; Sun, 18 Feb 2024 18:57:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708282677; cv=none; b=OJseM3BEauP2lSo8Ys7Wd/NUTf8IdNHsgmhSGXWJoU97l0iPdBehceeR4CZf45zTzuehCj13B4PNDXTYSakU1VmvFA5Hm3e4/IZudCMeJijxU+Xj132xB0amLBWeKbgSO7ZELZY7LchKLc04aDbrmQXg9rHMHXjgAsd94diuRP4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708282677; c=relaxed/simple; bh=aVOu1/bqDAARdrnRU5+DODTSrgXpJ65t9RLdNz7m7TU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ZQzItlAGpVE8bUo+Gye7NxtglewX8vomZEQktW7GCjhbY4OZCdG6kP/wNGMnl9LMJy8Tlh45T9wNWcMKsv2TXkWMoQvGfQH+0V6JIDzlgUBntiBm1ACqiTsYnGKG+BonfKuR8Mx82NCCuzgPzu3MWzBwcQEVX4deDQO6RRlj7Mo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=QP9FA40Y; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=FhOTMESp; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="QP9FA40Y"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="FhOTMESp" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1708282672; 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=glYrKDUJ7lHx0vPgFl5st9OXHzyL6p/mgGcT2k0j/yc=; b=QP9FA40YAYELeVxUBZi0Zk2entx086hATCdFn7fwEWkwoePQdmQY0Zj0BaqefkCK4vyKhE yRkaQCR/GZDq+3tMY85Aso10KSnz9ewFoQR0uzw5xX7UEx2kQvU6snT7OpbrX6IUFeAuZ8 fOSXwvqW+QtcEVp3Oojb3qIw7rd/+Txlt4JS0gailqcqmpWZNwOF1AWvEl9rg0nLp1KJuz pO222FA/6ucaoV7cZ+z7J+PSOdW/EK/nUEaEJzVNFX95ipdWO4CLM5FJhy2oe4RcPyY6zw JrZHmJEV1me0Qx4e7u6kZE3qICmMgHtfiV/CuPCLnfNVRHS1Rgz5ka538z3gfw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1708282672; 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=glYrKDUJ7lHx0vPgFl5st9OXHzyL6p/mgGcT2k0j/yc=; b=FhOTMESp09Y0esdlb4LAnktBJn/wIjVMQZnSHidLDRzBe14BT9TOvFuRuyAZ4oZ7T1ZDDm /HeXGmslX87eNKBg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v2 14/26] printk: nbcon: Provide function to flush using write_atomic() Date: Sun, 18 Feb 2024 20:03:14 +0106 Message-Id: <20240218185726.1994771-15-john.ogness@linutronix.de> In-Reply-To: <20240218185726.1994771-1-john.ogness@linutronix.de> References: <20240218185726.1994771-1-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Thomas Gleixner Provide nbcon_atomic_flush_all() to perform flushing of all registered nbcon consoles using their write_atomic() callback. Like with legacy consoles, the nbcon consoles are flushed one record per console. This allows all nbcon consoles to print lines pseudo-simultaneously, rather than one console waiting for the full ringbuffer to dump to another console before printing anything. Unlike console_flush_all(), nbcon_atomic_flush_all() will only flush up through the newest record at the time of the call. This prevents a CPU from printing unbounded when other CPUs are adding records. Perform nbcon console atomic flushing in console_flush_on_panic(). This function is not only used in panic() but also other locations where there may be stored messages that need to be flushed. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Reviewed-by: Petr Mladek --- kernel/printk/internal.h | 2 + kernel/printk/nbcon.c | 100 ++++++++++++++++++++++++++++++++++++++- kernel/printk/printk.c | 2 + 3 files changed, 102 insertions(+), 2 deletions(-) diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 6780911fa8f2..d9a5205692fc 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -77,6 +77,7 @@ void nbcon_seq_force(struct console *con, u64 seq); bool nbcon_alloc(struct console *con); void nbcon_init(struct console *con); void nbcon_free(struct console *con); +void nbcon_atomic_flush_all(void); =20 /* * Check if the given console is currently capable and allowed to print @@ -131,6 +132,7 @@ static inline void nbcon_seq_force(struct console *con,= u64 seq) { } static inline bool nbcon_alloc(struct console *con) { return false; } static inline void nbcon_init(struct console *con) { } static inline void nbcon_free(struct console *con) { } +static inline void nbcon_atomic_flush_all(void) { } =20 static inline bool console_is_usable(struct console *con, short flags) { r= eturn false; } =20 diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index 02e8fdc1ea43..2eb2929c1027 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -539,7 +539,6 @@ static struct printk_buffers panic_nbcon_pbufs; * in an unsafe state. Otherwise, on success the caller may assume * the console is not in an unsafe state. */ -__maybe_unused static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) { unsigned int cpu =3D smp_processor_id(); @@ -841,7 +840,6 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); * 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); @@ -930,6 +928,104 @@ static bool nbcon_emit_next_record(struct nbcon_write= _context *wctxt) return nbcon_context_exit_unsafe(ctxt); } =20 +/** + * nbcon_atomic_emit_one - Print one record for an nbcon console using the + * write_atomic() callback + * @wctxt: An initialized write context struct to use + * for this context + * + * Return: False if the given console could not print a record or there + * are no more records to print, otherwise true. + * + * This is an internal helper to handle the locking of the console before + * calling nbcon_emit_next_record(). + */ +static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + + if (!nbcon_context_try_acquire(ctxt)) + return false; + + /* + * nbcon_emit_next_record() returns false when the console was + * handed over or taken over. In both cases the context is no + * longer valid. + */ + if (!nbcon_emit_next_record(wctxt)) + return false; + + nbcon_context_release(ctxt); + + return ctxt->backlog; +} + +/** + * __nbcon_atomic_flush_all - Flush all nbcon consoles using their + * write_atomic() callback + * @stop_seq: Flush up until this record + */ +static void __nbcon_atomic_flush_all(u64 stop_seq) +{ + struct nbcon_write_context wctxt =3D { }; + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(&wctxt, ctxt); + struct console *con; + bool any_progress; + int cookie; + + do { + any_progress =3D false; + + cookie =3D console_srcu_read_lock(); + for_each_console_srcu(con) { + short flags =3D console_srcu_read_flags(con); + unsigned long irq_flags; + + if (!(flags & CON_NBCON)) + continue; + + if (!console_is_usable(con, flags)) + continue; + + if (nbcon_seq_read(con) >=3D stop_seq) + continue; + + memset(ctxt, 0, sizeof(*ctxt)); + ctxt->console =3D con; + ctxt->spinwait_max_us =3D 2000; + ctxt->prio =3D NBCON_PRIO_NORMAL; + + /* + * Atomic flushing does not use console driver + * synchronization (i.e. it does not hold the port + * lock for uart consoles). Therefore IRQs must be + * disabled to avoid being interrupted and then + * calling into a driver that will deadlock trying + * acquire console ownership. + */ + local_irq_save(irq_flags); + + any_progress |=3D nbcon_atomic_emit_one(&wctxt); + + local_irq_restore(irq_flags); + } + console_srcu_read_unlock(cookie); + } while (any_progress); +} + +/** + * nbcon_atomic_flush_all - Flush all nbcon consoles using their + * write_atomic() callback + * + * Flush the backlog up through the currently newest record. Any new + * records added while flushing will not be flushed. This is to avoid + * one CPU printing unbounded because other CPUs continue to add records. + */ +void nbcon_atomic_flush_all(void) +{ + __nbcon_atomic_flush_all(prb_next_reserve_seq(prb)); +} + /** * 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 9d56ce5837f9..ea170ade4d42 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3169,6 +3169,8 @@ void console_flush_on_panic(enum con_flush_mode mode) console_srcu_read_unlock(cookie); } =20 + nbcon_atomic_flush_all(); + console_flush_all(false, &next_seq, &handover); } =20 --=20 2.39.2