From patchwork Sun Dec 6 15:56:21 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pavel Begunkov X-Patchwork-Id: 11954149 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6494C4361B for ; Sun, 6 Dec 2020 16:00:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FD0622D06 for ; Sun, 6 Dec 2020 16:00:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727132AbgLFQAj (ORCPT ); Sun, 6 Dec 2020 11:00:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58870 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726602AbgLFQAc (ORCPT ); Sun, 6 Dec 2020 11:00:32 -0500 Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com [IPv6:2a00:1450:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A01FC0613D3 for ; Sun, 6 Dec 2020 07:59:51 -0800 (PST) Received: by mail-wm1-x342.google.com with SMTP id f190so11437044wme.1 for ; Sun, 06 Dec 2020 07:59:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:subject:date:message-id:in-reply-to:references:mime-version :content-transfer-encoding; bh=MTZNTj9112GUR4EWB5wrXSfr5LJhNHZqAO0IoO3ucUo=; b=o4GoEIXKzg7vekzOMwGVL357Bq/bcuGoN14zfqaYgUN/m1GBqstfjKqC0tAT31xPqG i4aAhxYVrfvtR1F6vpELJWpDM7ab+ZtEwACi+gco2FS9ZoZ8ps6q9QFNwQzA1aOfFMY2 ELhkphTRqiOiFLpaCB2oZ2N9oHjHR50cJVJ4ejV3yjGpY6Kt2F1Uowkn8q9ijXaW9Xok VyNhdfQ5aXBrRSBG74Q1JEMf3xRPMpOfDJXU58fPDikU/6/othq9de73jJPaVVbHGRvn khgpXp+Hr9/cg8hIoBHJQ7/zU9CzIwnSvtaAhrfehgB1ICibrNP/gUU3Img+VPfQtBKZ XVuA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=MTZNTj9112GUR4EWB5wrXSfr5LJhNHZqAO0IoO3ucUo=; b=SG1+EJlv+CwTGcCCmMrE4Ugzx/bHDI4EfvCZe3TQ5LEWZ6Qbc7yPrnrNBAd/bukI+9 Y9r0NA1DFKuz3rnqUVatvjql50zvk0wiyiFUL19yE29DOSjTNc9yrpRZoBf4sFRJ+plz MgSV9N797eNeVinDndBkVCx/3KXiiXA4CYhKiwOqCz4UMdt0ttDQUU0kyE6fIs9fuaeR LbLcN9HA6jU4dA79N/woXQt82DNKjf+KbRIh6QAgMaDK+KbZgqHEJY2eehj7jb37Ve3s gp8vnKsEuHESHIqJrg/3SLvroX8BYp6PBUPbZYc2jCDTdvWcXisNW9h4HTS0B4V/Jmj3 O2FQ== X-Gm-Message-State: AOAM531l21pifcsNZBaNkZcvEbjOrhigV6fJxYKu0xyXLtn/7w+NaJqv /zVcrAS3Z+9TEl9BZnWgynY= X-Google-Smtp-Source: ABdhPJxqZCrR30Ujd19DOYKuCfAnIYGe73fUEY/5nhMtWKU/UckDhLY7VoEnuYnqEaHAVX7/lFOueg== X-Received: by 2002:a1c:a9c8:: with SMTP id s191mr14215072wme.89.1607270390434; Sun, 06 Dec 2020 07:59:50 -0800 (PST) Received: from localhost.localdomain ([185.69.145.92]) by smtp.gmail.com with ESMTPSA id h14sm9933355wrx.37.2020.12.06.07.59.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 06 Dec 2020 07:59:50 -0800 (PST) From: Pavel Begunkov To: Chris Mason , Josef Bacik , David Sterba , linux-btrfs@vger.kernel.org Subject: [PATCH v3 2/3] btrfs: fix racy access to discard_ctl data Date: Sun, 6 Dec 2020 15:56:21 +0000 Message-Id: X-Mailer: git-send-email 2.24.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Because only one discard worker may be running at any given point, it could have been safe to modify ->prev_discard, etc. without synchronisation, if not for @override flag in btrfs_discard_schedule_work() and delayed_work_pending() returning false while workfn is running. That may lead lead to torn reads of u64 for some architectures, but that's not a big problem as only slightly affects the discard rate. Suggested-by: Josef Bacik Signed-off-by: Pavel Begunkov --- fs/btrfs/discard.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c index 36431d7e1334..d641f451f840 100644 --- a/fs/btrfs/discard.c +++ b/fs/btrfs/discard.c @@ -477,13 +477,6 @@ static void btrfs_discard_workfn(struct work_struct *work) discard_ctl->discard_extent_bytes += trimmed; } - /* - * Updated without locks as this is inside the workfn and nothing else - * is reading the values - */ - discard_ctl->prev_discard = trimmed; - discard_ctl->prev_discard_time = ktime_get_ns(); - /* Determine next steps for a block_group */ if (block_group->discard_cursor >= btrfs_block_group_end(block_group)) { if (discard_state == BTRFS_DISCARD_BITMAPS) { @@ -499,7 +492,10 @@ static void btrfs_discard_workfn(struct work_struct *work) } } + now = ktime_get_ns(); spin_lock(&discard_ctl->lock); + discard_ctl->prev_discard = trimmed; + discard_ctl->prev_discard_time = now; discard_ctl->block_group = NULL; spin_unlock(&discard_ctl->lock);