From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 22A5C1428ED; Sun, 24 Mar 2024 22:37:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711319858; cv=none; b=DykJUVJw+trLF+eFXgQQzTknizSqwx6SgCFsG5FdR11Ptf64jhnC8BwV5b2pvPU0PyWxY1ruB8V0oAJUzglrKpUtVPGjEbUAA3U/Kl5FSk3QWQN1cqoEMoMUewtz6SmQSJTUQLGMkZLSqnrI4Efdo5ziCFW+4HNOwQF0/Ll33Fc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711319858; c=relaxed/simple; bh=Hb/NsZOhMbQg490AAjzJrWojSX3thYXJ3sqhmuaCxWw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IlDaR3lEod8IT6lnyUGSLeREfubhDzrmSzlnu+9skRbimSYu7/c7hbQBOCp7z5qvuqig0GBCeTc/a/Biyzml+n/oxokUC0HSLibab3BAyikKmw0PYqOapBv+RqJDlgA+F/mGveD1+3DdutaIDy+c3cflOtsp6Oi59X/A23ciQvc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QF+edNKD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QF+edNKD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14CD4C433C7; Sun, 24 Mar 2024 22:37:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711319857; bh=Hb/NsZOhMbQg490AAjzJrWojSX3thYXJ3sqhmuaCxWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QF+edNKDo5S/Y6frqX2lajIKQ173w4pXug5mTrn0m6pffN+flOcszENcvEamdI7yB uOCTCkHblUkp9pQ2BtoR/9BAh0rdrOHVmS306IOam7AYIA4K2Tfef6AAk/uN9dEspK ghNOICi+qHq6H9VGpRTGcblgPfeG596wPwZxc/N1mEyagYhfpoR6JA8SWhTGPrtc95 dCakJ/cI6ynjstBFHMJYtSZMtagAg+y7LYhZRmD4sAC7cI6wUNAsPIDkPTv4AUaWeu impo/iYjeEVOCrhlDxkai+OBo7jAWk7uBnovRAJb1jqCt9SGvSYmYVMtiRgr48sPLQ N5Mt7Oa2s0lnA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: John Ogness , Petr Mladek , Sasha Levin Subject: [PATCH 6.8 161/715] printk: Wait for all reserved records with pr_flush() Date: Sun, 24 Mar 2024 18:25:40 -0400 Message-ID: <20240324223455.1342824-162-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324223455.1342824-1-sashal@kernel.org> References: <20240324223455.1342824-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: John Ogness [ Upstream commit ac7d7844c64d15603daa3e905a311ddcfbb4bc91 ] Currently pr_flush() will only wait for records that were available to readers at the time of the call (using prb_next_seq()). But there may be more records (non-finalized) that have 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. Add a new ringbuffer function prb_next_reserve_seq() to return the sequence number following the most recently reserved record. This guarantees that pr_flush() will wait until all current printk() messages (completed or in progress) have been printed. Fixes: 3b604ca81202 ("printk: add pr_flush()") Signed-off-by: John Ogness Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/20240207134103.1357162-10-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin --- kernel/printk/printk.c | 2 +- kernel/printk/printk_ringbuffer.c | 105 ++++++++++++++++++++++++++++++ kernel/printk/printk_ringbuffer.h | 1 + 3 files changed, 107 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index f2444b581e16c..d9420207282ac 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3761,7 +3761,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre might_sleep(); - seq = prb_next_seq(prb); + seq = prb_next_reserve_seq(prb); /* 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_ringbuffer.c index 4ce1826dc9426..d152b6bd35c9a 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -1974,6 +1974,111 @@ static u64 prb_first_seq(struct printk_ringbuffer *rb) return seq; } +/** + * 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 = &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 = desc_last_finalized_seq(rb); + + /* + * @head_id is loaded after @last_finalized_seq to ensure that + * it points to the record with @last_finalized_seq or newer. + * + * 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 = atomic_long_read(&desc_ring->head_id); /* LMM(prb_next_reserve_seq:A) */ + + d = to_desc(desc_ring, last_finalized_seq); + state_var = &d->state_var; + + /* Extract the ID, used to specify the descriptor to read. */ + last_finalized_id = DESC_ID(atomic_long_read(state_var)); + + /* Ensure @last_finalized_id is correct. */ + err = desc_read_finalized_seq(desc_ring, last_finalized_id, last_finalized_seq, &desc); + + if (err == -EINVAL) { + if (last_finalized_seq == 0) { + /* + * No record has been finalized or even reserved yet. + * + * The @head_id is initialized such that the first + * increment will yield the first record (seq=0). + * Handle it separately to avoid a negative @diff + * below. + */ + if (head_id == DESC0_ID(desc_ring->count_bits)) + return 0; + + /* + * One or more descriptors are already reserved. Use + * the descriptor ID of the first one (@seq=0) for + * the @diff below. + */ + last_finalized_id = DESC0_ID(desc_ring->count_bits) + 1; + } else { + /* Record must have been overwritten. Try again. */ + goto try_again; + } + } + + /* Diff of known descriptor IDs to compute related sequence numbers. */ + diff = head_id - last_finalized_id; + + /* + * @head_id points to the most recently reserved record, but this + * function returns the sequence number that will be assigned to the + * next (not yet reserved) record. Thus +1 is needed. + */ + return (last_finalized_seq + diff + 1); +} + /* * Non-blocking read of a record. Updates @seq to the last finalized record * (which may have no data available). diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h index 70457916d577d..5aebe97bd4afc 100644 --- a/kernel/printk/printk_ringbuffer.h +++ b/kernel/printk/printk_ringbuffer.h @@ -380,6 +380,7 @@ bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, 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); #ifdef CONFIG_64BIT -- 2.43.0