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 B681D143C5F; Sun, 24 Mar 2024 22:37:40 +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=1711319860; cv=none; b=AmV/K4O9JKIOvyj6dvq0apqa0M7QxPF/LJ9HqvQLjjjqa7vRGy4wXXJk6cEE41snDmbmAx0A0cV0NpFY2i1EHq1QqiNFkBsiSxYAHm6FrnKg9NvWl8/t1gXK/ivMNajwPb5FQlBjrV0xFkfvBop+A6+zUHUHDdj8Pu5q/3GpSFI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711319860; c=relaxed/simple; bh=RN/Gjmnw+EceYASHDrod4BrDl4PiVcldLWDVe0b9138=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SwuJJDL8StOCS26Mo9x8vb0ulG8u5TeGk51ju5IlW+8uCrdA/zBAjsvYQeHu96v6a/IJX8nT32fZbb93JEcr4Kwd0XGeMHjDngAfRYJLVYDvY2RQO8m98fplHaz9mcmGRL1i2JmNYikL0sjtCZEGBTVuB4rN6Ai02pIVQi8nNIc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dSCkxZ4Y; 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="dSCkxZ4Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE66CC43390; Sun, 24 Mar 2024 22:37:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711319860; bh=RN/Gjmnw+EceYASHDrod4BrDl4PiVcldLWDVe0b9138=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dSCkxZ4Yr7a4dCWC1uYRvK6OvlvtdYtDVugxSlUpGGXAjfNJdXNYjQ60bLEsHmRwE GScy7NgVvUsgHla8H75nHeAlOnyFId1BKmKzwr5YSKpopRFsJ+c7bmIZwWU93yKeop SBm2stQY6XgHix61gv2l+CyOvtkK29U76P48SvjzK4aRPgkivOPXum/5DmBlsnK2cq +tBpjyy4TEofbuk/6PuoxRygpeDcqda4Wm2dJ1vWVv7AmlBSdVRnSwrDbOgg+RDuiE +bYkvhQYMcoSj/YXyv6R6A6vRfoEMtr6rQXx5EB1SYlUaK+a/tCi2jxadM+aoBEJkN 53shRrln8SNLA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: John Ogness , Petr Mladek , Sasha Levin Subject: [PATCH 6.8 164/715] printk: ringbuffer: Skip non-finalized records in panic Date: Sun, 24 Mar 2024 18:25:43 -0400 Message-ID: <20240324223455.1342824-165-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 b1c4c67a5e90db8fbdb5b5504fe16e17b564cca8 ] Normally a reader will stop once reaching a non-finalized record. However, when a panic happens, writers from other CPUs (or an interrupted context on the panic CPU) may have been writing a record and were unable to finalize it. The panic CPU will reserve/commit/finalize its panic records, but these will be located after the non-finalized records. This results in panic() not flushing the panic messages. Extend _prb_read_valid() to skip over non-finalized records if on the panic CPU. Fixes: 896fbe20b4e2 ("printk: use the lockless ringbuffer") Signed-off-by: John Ogness Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/20240207134103.1357162-11-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin --- kernel/printk/printk_ringbuffer.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 97ec25d227976..3d98232902cfd 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -2087,6 +2087,10 @@ u64 prb_next_reserve_seq(struct printk_ringbuffer *rb) * * On failure @seq is updated to a record that is not yet available to the * reader, but it will be the next record available to the reader. + * + * Note: When the current CPU is in panic, this function will skip over any + * non-existent/non-finalized records in order to allow the panic CPU + * to print any and all records that have been finalized. */ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, struct printk_record *r, unsigned int *line_count) @@ -2109,8 +2113,28 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, (*seq)++; } else { - /* Non-existent/non-finalized record. Must stop. */ - return false; + /* + * Non-existent/non-finalized record. Must stop. + * + * For panic situations it cannot be expected that + * non-finalized records will become finalized. But + * there may be other finalized records beyond that + * need to be printed for a panic situation. If this + * is the panic CPU, skip this + * non-existent/non-finalized record unless it is + * at or beyond the head, in which case it is not + * possible to continue. + * + * Note that new messages printed on panic CPU are + * finalized when we are here. The only exception + * might be the last message without trailing newline. + * But it would have the sequence number returned + * by "prb_next_reserve_seq() - 1". + */ + if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb))) + (*seq)++; + else + return false; } } -- 2.43.0