From nobody Wed Dec 31 08:46:23 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 5B60BC4332F for ; Mon, 6 Nov 2023 21:07:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233170AbjKFVHw (ORCPT ); Mon, 6 Nov 2023 16:07:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57764 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233102AbjKFVHk (ORCPT ); Mon, 6 Nov 2023 16:07:40 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A4DE7103 for ; Mon, 6 Nov 2023 13:07:37 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1699304855; 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=kyZ2jAekG9IbA8OHPwAlE8+iwKYLcZ73K8RQgyikDwc=; b=hoDow6cmR6fMaIE4IEz8T8ZOa9WAsRAIZ1laV7umbzSbt5N8y2x2sO+SEOaC0qXJgBq0cN HEy9osDwNbibWwsvVQvTwmQxALb/YuUKRlWjPncmw6OPDe7hHkUmhNI7smOxwew9qPX0Pq 5EB4HTobjMmvA3On+SoaH6IIwXB9P+1b4ZDYfb/vHAmXFZHB1yfpAL5sGW30R8TlCgzZym Xj2TupQPiAbEdqrVVXILcrBfu1cjcPkcWvW2P1kPCLRMPS341VzeJp3sFWt1uVLmiI7MKZ k1e8LB08vDy7bVHANZ8tiyNOjMH8g634lXyeERfrncWjMnDybu5U62N8OagTXw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1699304855; 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=kyZ2jAekG9IbA8OHPwAlE8+iwKYLcZ73K8RQgyikDwc=; b=NeUa92hCHMV8isuc4k3GcjK6dGlvkA0s8ZlE8vv05kzT4Cr+cL2RHKKjGmyq2k7xGzaAZS D2KlUcMMEzB78VCw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v2 6/9] printk: Wait for all reserved records with pr_flush() Date: Mon, 6 Nov 2023 22:13:27 +0106 Message-Id: <20231106210730.115192-7-john.ogness@linutronix.de> In-Reply-To: <20231106210730.115192-1-john.ogness@linutronix.de> References: <20231106210730.115192-1-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" Currently pr_flush() will only wait for records that were available to readers at the time of the call. But there may be more records (non-finalized) with following finalized records. pr_flush() should wait for these to print as well. Particularly because any trailing finalized records may be the messages that the calling context wants to ensure are printed. Fixes: 3b604ca81202 ("printk: add pr_flush()") Signed-off-by: John Ogness --- kernel/printk/printk.c | 2 +- kernel/printk/printk_ringbuffer.c | 96 +++++++++++++++++++++++++++++++ kernel/printk/printk_ringbuffer.h | 1 + 3 files changed, 98 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 82dc2c7949b7..f3a7f5a6f6f8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3755,7 +3755,7 @@ static bool __pr_flush(struct console *con, int timeo= ut_ms, bool reset_on_progre =20 might_sleep(); =20 - seq =3D prb_next_seq(prb); + seq =3D prb_next_reserve_seq(prb); =20 /* Flush the consoles so that records up to @seq are printed. */ console_lock(); diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringb= uffer.c index 7c121fd68330..dc83569d3a3a 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -2012,6 +2012,102 @@ static u64 prb_first_seq(struct printk_ringbuffer *= rb) return seq; } =20 +/** + * prb_next_reserve_seq() - Get the sequence number after the most recently + * reserved record. + * + * @rb: The ringbuffer to get the sequence number from. + * + * This is the public function available to readers to see what sequence + * number will be assigned to the next reserved record. + * + * Note that depending on the situation, this value can be equal to or + * higher than the sequence number returned by prb_next_seq(). + * + * Context: Any context. + * Return: The sequence number that will be assigned to the next record + * reserved. + */ +u64 prb_next_reserve_seq(struct printk_ringbuffer *rb) +{ + struct prb_desc_ring *desc_ring =3D &rb->desc_ring; + unsigned long last_finalized_id; + atomic_long_t *state_var; + u64 last_finalized_seq; + unsigned long head_id; + struct prb_desc desc; + unsigned long diff; + struct prb_desc *d; + int err; + + /* + * It may not be possible to read a sequence number for @head_id. + * So the ID of @last_finailzed_seq is used to calculate what the + * sequence number of @head_id will be. + */ + +try_again: + last_finalized_seq =3D desc_last_finalized_seq(desc_ring); + + /* + * @head_id is loaded after @last_finalized_seq to ensure that it is + * at or beyond @last_finalized_seq. + * + * Memory barrier involvement: + * + * If desc_last_finalized_seq:A reads from + * desc_update_last_finalized:A, then + * prb_next_reserve_seq:A reads from desc_reserve:D. + * + * Relies on: + * + * RELEASE from desc_reserve:D to desc_update_last_finalized:A + * matching + * ACQUIRE from desc_last_finalized_seq:A to prb_next_reserve_seq:A + * + * Note: desc_reserve:D and desc_update_last_finalized:A can be + * different CPUs. However, the desc_update_last_finalized:A CPU + * (which performs the release) must have previously seen + * desc_read:C, which implies desc_reserve:D can be seen. + */ + head_id =3D atomic_long_read(&desc_ring->head_id); /* LMM(prb_next_reserv= e_seq:A) */ + + d =3D to_desc(desc_ring, last_finalized_seq); + state_var =3D &d->state_var; + + /* Extract the ID, used to specify the descriptor to read. */ + last_finalized_id =3D DESC_ID(atomic_long_read(state_var)); + + /* Ensure @last_finalized_id is correct. */ + err =3D desc_read_finalized_seq(desc_ring, last_finalized_id, last_finali= zed_seq, &desc); + + if (err =3D=3D -EINVAL) { + if (last_finalized_seq =3D=3D 0) { + /* + * @last_finalized_seq still contains its initial + * value. Probably no record has been finalized yet. + * This means the ringbuffer is not yet full and the + * @head_id value can be used directly (subtracting + * off its initial value). + * + * Because of hack#2 of the bootstrapping phase, the + * @head_id initial value must be handled separately. + */ + if (head_id =3D=3D DESC0_ID(desc_ring->count_bits)) + return 0; + + last_finalized_id =3D DESC0_ID(desc_ring->count_bits) + 1; + } else { + /* Record must have been overwritten. Try again. */ + goto try_again; + } + } + + diff =3D head_id - last_finalized_id; + + return (last_finalized_seq + diff); +} + /* * Non-blocking read of a record. * diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringb= uffer.h index 5c09061433f3..b48b44ecbe6d 100644 --- a/kernel/printk/printk_ringbuffer.h +++ b/kernel/printk/printk_ringbuffer.h @@ -394,5 +394,6 @@ bool prb_read_valid_info(struct printk_ringbuffer *rb, = u64 seq, =20 u64 prb_first_valid_seq(struct printk_ringbuffer *rb); u64 prb_next_seq(struct printk_ringbuffer *rb); +u64 prb_next_reserve_seq(struct printk_ringbuffer *rb); =20 #endif /* _KERNEL_PRINTK_RINGBUFFER_H */ --=20 2.39.2