From nobody Fri Sep 20 20:36:05 2024 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 BA96CC77B72 for ; Wed, 12 Apr 2023 11:25:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230207AbjDLLZO (ORCPT ); Wed, 12 Apr 2023 07:25:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230294AbjDLLYw (ORCPT ); Wed, 12 Apr 2023 07:24:52 -0400 Received: from mailgw02.mediatek.com (unknown [210.61.82.184]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0596740F2; Wed, 12 Apr 2023 04:24:27 -0700 (PDT) X-UUID: 8c6c1186d92411edb6b9f13eb10bd0fe-20230412 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=mediatek.com; s=dk; h=Content-Type:MIME-Version:Message-ID:Date:Subject:CC:To:From; bh=QP7sQjwZzKXI0b464YWLSZqML8grLgd1UX3dg7K3rSA=; b=QgezrJLGrXlXX/1TvSBmalnHr1z23JCPcE6nXNPDzDumPGVvmBymdwaX/VY3FHSV1XDXcQ58DfyjfdqVQFBzKaV5jYdkdPfK/vNTEasXbZaxTNvUndgxiRjVVJNq0n2xZG/Iv1BVqCGRLc0xEvw44nE09OIZmDVcrl1wMpBlK98=; X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.1.22,REQID:228adf8c-7605-4685-83d6-6ad6e972d08f,IP:0,U RL:0,TC:0,Content:-25,EDM:0,RT:0,SF:95,FILE:0,BULK:0,RULE:Release_Ham,ACTI ON:release,TS:70 X-CID-INFO: VERSION:1.1.22,REQID:228adf8c-7605-4685-83d6-6ad6e972d08f,IP:0,URL :0,TC:0,Content:-25,EDM:0,RT:0,SF:95,FILE:0,BULK:0,RULE:Spam_GS981B3D,ACTI ON:quarantine,TS:70 X-CID-META: VersionHash:120426c,CLOUDID:84f2b9ea-db6f-41fe-8b83-13fe7ed1ef52,B ulkID:2304121924148FJCQDB8,BulkQuantity:0,Recheck:0,SF:38|29|28|17|19|48,T C:nil,Content:0,EDM:-3,IP:nil,URL:11|1,File:nil,Bulk:nil,QS:nil,BEC:nil,CO L:0,OSI:0,OSA:0,AV:0 X-CID-BVR: 0 X-CID-BAS: 0,_,0,_ X-UUID: 8c6c1186d92411edb6b9f13eb10bd0fe-20230412 Received: from mtkmbs10n1.mediatek.inc [(172.21.101.34)] by mailgw02.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-GCM-SHA384 256/256) with ESMTP id 1256624878; Wed, 12 Apr 2023 19:24:11 +0800 Received: from mtkmbs13n2.mediatek.inc (172.21.101.108) by mtkmbs10n2.mediatek.inc (172.21.101.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.25; Wed, 12 Apr 2023 19:24:10 +0800 Received: from mtksdccf07.mediatek.inc (172.21.84.99) by mtkmbs13n2.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.2.1118.25 via Frontend Transport; Wed, 12 Apr 2023 19:24:10 +0800 From: Tze-nan Wu To: , CC: , , , , , , AngeloGioacchino Del Regno , "Paul E. McKenney" , , , , Subject: [PATCH v4] ring-buffer: Ensure proper resetting of atomic variables in ring_buffer_reset_online_cpus Date: Wed, 12 Apr 2023 19:23:56 +0800 Message-ID: <20230412112401.25081-1-Tze-nan.Wu@mediatek.com> X-Mailer: git-send-email 2.18.0 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" 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. Cc: stable@vger.kernel.org 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 --- Changes from v1 to v3: https://lore.kernel.org/all/20230408052226.25268-1-T= ze-nan.Wu@mediatek.com/ - Declare the cpumask variable statically rather than dynamically. Changes from v2 to v3: https://lore.kernel.org/all/20230409024616.31099-1-T= ze-nan.Wu@mediatek.com/ - Considering holding cpu_hotplug_lock too long because of the synchronize_rcu(), maybe it's better to prevent the issue by copying cpu_online_mask at the entry of the function as V1 does, instead of using cpus_read_lock(). Changes from v3 to v4: https://lore.kernel.org/all/20230410073512.13362-1-T= ze-nan.Wu@mediatek.com/ - Considering that the size of cpumask may not be too big on some machines We no longer adopt the approach of copying cpumask at the beginning of the function. Instead, we ensure that atomic variables have been set up before atomic_sub() is called. - Change the title of the patch. --- kernel/trace/ring_buffer.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 76a2d91eecad..8c647d8b5bb4 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5361,20 +5361,28 @@ 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); +#define RESET_BIT (1 << 30) + 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 2.18.0