From nobody Thu Feb 12 07:39:12 2026 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 439FDC77B78 for ; Wed, 26 Apr 2023 17:18:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235085AbjDZRSU (ORCPT ); Wed, 26 Apr 2023 13:18:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40646 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234756AbjDZRRy (ORCPT ); Wed, 26 Apr 2023 13:17:54 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21883525D; Wed, 26 Apr 2023 10:17:53 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5352F63706; Wed, 26 Apr 2023 17:17:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D009C4339B; Wed, 26 Apr 2023 17:17:52 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.96) (envelope-from ) id 1prim7-005Kcf-0k; Wed, 26 Apr 2023 13:17:51 -0400 Message-ID: <20230426171751.044554153@goodmis.org> User-Agent: quilt/0.66 Date: Wed, 26 Apr 2023 13:17:13 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Andrew Morton , stable@vger.kernel.org, npiggin@gmail.com, Cheng-Jui Wang , Tze-nan Wu Subject: [for-next][PATCH 10/11] ring-buffer: Ensure proper resetting of atomic variables in ring_buffer_reset_online_cpus References: <20230426171703.202523909@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tze-nan Wu In ring_buffer_reset_online_cpus, the buffer_size_kb write operation may permanently fail if the cpu_online_mask changes between two for_each_online_buffer_cpu loops. The number of increases and decreases on both cpu_buffer->resize_disabled and cpu_buffer->record_disabled may be inconsistent, causing some CPUs to have non-zero values for these atomic variables after the function returns. This issue can be reproduced by "echo 0 > trace" while hotplugging cpu. After reproducing success, we can find out buffer_size_kb will not be functional anymore. To prevent leaving 'resize_disabled' and 'record_disabled' non-zero after ring_buffer_reset_online_cpus returns, we ensure that each atomic variable has been set up before atomic_sub() to it. Link: https://lore.kernel.org/linux-trace-kernel/20230426062027.17451-1-Tze= -nan.Wu@mediatek.com Cc: stable@vger.kernel.org Cc: Cc: npiggin@gmail.com Fixes: b23d7a5f4a07 ("ring-buffer: speed up buffer resets by avoiding synch= ronize_rcu for each CPU") Reviewed-by: Cheng-Jui Wang Signed-off-by: Tze-nan Wu Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 58be5b409f72..9a0cb94c3972 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5326,6 +5326,9 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffe= r, int cpu) } EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu); =20 +/* Flag to ensure proper resetting of atomic variables */ +#define RESET_BIT (1 << 30) + /** * ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer * @buffer: The ring buffer to reset a per cpu buffer of @@ -5342,20 +5345,27 @@ void ring_buffer_reset_online_cpus(struct trace_buf= fer *buffer) for_each_online_buffer_cpu(buffer, cpu) { cpu_buffer =3D buffer->buffers[cpu]; =20 - atomic_inc(&cpu_buffer->resize_disabled); + atomic_add(RESET_BIT, &cpu_buffer->resize_disabled); atomic_inc(&cpu_buffer->record_disabled); } =20 /* Make sure all commits have finished */ synchronize_rcu(); =20 - for_each_online_buffer_cpu(buffer, cpu) { + for_each_buffer_cpu(buffer, cpu) { cpu_buffer =3D buffer->buffers[cpu]; =20 + /* + * If a CPU came online during the synchronize_rcu(), then + * ignore it. + */ + if (!(atomic_read(&cpu_buffer->resize_disabled) & RESET_BIT)) + continue; + reset_disabled_cpu_buffer(cpu_buffer); =20 atomic_dec(&cpu_buffer->record_disabled); - atomic_dec(&cpu_buffer->resize_disabled); + atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled); } =20 mutex_unlock(&buffer->mutex); --=20 2.39.2