From nobody Fri Sep 20 20:39:41 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 6341EC7618E for ; Wed, 26 Apr 2023 06:21:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239509AbjDZGVA (ORCPT ); Wed, 26 Apr 2023 02:21:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239564AbjDZGUz (ORCPT ); Wed, 26 Apr 2023 02:20:55 -0400 Received: from mailgw02.mediatek.com (unknown [210.61.82.184]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9597270E; Tue, 25 Apr 2023 23:20:47 -0700 (PDT) X-UUID: 794dd5d6e3fa11edb6b9f13eb10bd0fe-20230426 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=WU3jPIGaeYnCfh0tvdyVkWtQSLr3g7psnjDX46eOhxg=; b=GbSKqM7x6+AvT1faNKgkL/vxN79EpESReJMJScfZ1Fi83aDgJyGcIKP9mcWtbX4+wdVx9aVQ6CKdt23ZjxzKZGnLA5+MCCIFaLT3rtOhB1O3t9FokLGlUczzmqN4lau13DqqfkBePuZK6dX9Q+OktK6+2jkg0lGZUwtKvpv2D1c=; X-CID-CACHE: Type:Local,Time:202304261335+08,HitQuantity:1 X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.1.22,REQID:e7662229-cfa5-42fe-b90b-8bf1b00345f5,IP:0,U RL:0,TC:0,Content:-25,EDM:0,RT:0,SF:0,FILE:0,BULK:0,RULE:Release_Ham,ACTIO N:release,TS:-25 X-CID-META: VersionHash:120426c,CLOUDID:a5ec8aa2-8fcb-430b-954a-ba3f00fa94a5,B ulkID:nil,BulkQuantity:0,Recheck:0,SF:102,TC:nil,Content:0,EDM:-3,IP:nil,U RL:11|1,File:nil,Bulk:nil,QS:nil,BEC:nil,COL:0,OSI:0,OSA:0,AV:0 X-CID-BVR: 0 X-CID-BAS: 0,_,0,_ X-UUID: 794dd5d6e3fa11edb6b9f13eb10bd0fe-20230426 Received: from mtkmbs10n2.mediatek.inc [(172.21.101.183)] by mailgw02.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-GCM-SHA384 256/256) with ESMTP id 2123903616; Wed, 26 Apr 2023 14:20:43 +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 15.2.1118.26; Wed, 26 Apr 2023 14:20:41 +0800 Received: from mtksdccf07.mediatek.inc (172.21.84.99) by mtkmbs13n2.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.2.1118.26 via Frontend Transport; Wed, 26 Apr 2023 14:20:41 +0800 From: Tze-nan Wu To: , CC: , , , Tze-nan Wu , , , AngeloGioacchino Del Regno , "Paul E. McKenney" , , , , Subject: [PATCH v5] ring-buffer: Ensure proper resetting of atomic variables in ring_buffer_reset_online_cpus Date: Wed, 26 Apr 2023 14:20:23 +0800 Message-ID: <20230426062027.17451-1-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 v4 to v5: https://lore.kernel.org/lkml/20230412112401.25081-1-= Tze-nan.Wu@mediatek.com/ - Move the define before the function --- 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 76a2d91eecad..253ef85a9ec3 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5345,6 +5345,9 @@ 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 @@ -5361,20 +5364,27 @@ 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 2.18.0