From mboxrd@z Thu Jan 1 00:00:00 1970 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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 CA413C432C0 for ; Thu, 28 Nov 2019 03:45:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9F0E42166E for ; Thu, 28 Nov 2019 03:45:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hMo4zspO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727529AbfK1DpG (ORCPT ); Wed, 27 Nov 2019 22:45:06 -0500 Received: from mail-ed1-f52.google.com ([209.85.208.52]:42254 "EHLO mail-ed1-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727117AbfK1DpF (ORCPT ); Wed, 27 Nov 2019 22:45:05 -0500 Received: by mail-ed1-f52.google.com with SMTP id e10so1454085edv.9 for ; Wed, 27 Nov 2019 19:45:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=J+3BDIq39RSw0qnL/ejXv9XyH/mM2u4LYVIZ4oDLnhY=; b=hMo4zspO3xQ1DmZPzsB/dMPS0iR1LWd74Ro75lCLtBdX89uqU4V9k/WtuplMoCrrhl O9+HDlDYh4H96KU1fnk110zW7B8TZBVMA5x2+1tEurIQcFG3XHl2eyxmbknDxATfzrSE FpcTDGJepeWBV6/sAofLVjjdO95Dxbv7xPcyBNukp+sZXA125ozn66T6PmHpY5KTzm+g hegVo2+UsCPq6A5ekJqcTFaH4ieMrb2/H2uxx0k8ModUBeeIHqVwGoQBVSOFVcbdHwzn prsOfU4JZK1YMmRhqsMe9U0fDFvG7x3yIepj+gsqq0AwJp0Eo/2mRh6fpziFuxHJHKyZ vudg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=J+3BDIq39RSw0qnL/ejXv9XyH/mM2u4LYVIZ4oDLnhY=; b=j2wjmHw8NpEhcsvVFrAaKgiMTFRodq++/sdhMCPh+saacmWC/U/N711sTGpOSebP/D Jrg3TnJ2lFWMYXI/68aMwVRse+jQmkgtzWMxtjMiKhMUkmsLsnO6JpdSJrWCqawMdOWi 5zAYdS8wmq1AqC0l2e35NZjivzoDCu78oA8cr+6KpNNqkXVhczszZePWC4KUrOJzLw18 PoT/485bnQmYjSrEpqet4LNheh38CAgwcgQZsw+o8BMSV+IDFkiFwHpqxzOIyBIM/iXe uoUK4lvsI94djNDC8AnfD6WquZ0DDXjt9o4uRzpWTnieEF6VchVqGVTfjG2qYHeBsp69 pHMg== X-Gm-Message-State: APjAAAVm9flsktkKkPnbJRd/ufG17obH8CFUkUkbQUgx4DVqQgCQ1h8q GKxr2F3d7Js39h6h9lfU/veQx6xj/a9oKN+Fv+uYiWB6 X-Google-Smtp-Source: APXvYqxlEgd5dazYkQJZJPL63vcC5LyZDBUnssu78pbZXwIVRcpmFC7POC7xhzzp4vweZOGDrIbOWWPT5xoCfylx7Vw= X-Received: by 2002:a17:906:80c:: with SMTP id e12mr53327911ejd.59.1574912703863; Wed, 27 Nov 2019 19:45:03 -0800 (PST) MIME-Version: 1.0 From: Meng Xu Date: Wed, 27 Nov 2019 22:44:53 -0500 Message-ID: Subject: potential data race on disk_i_size in two btrfs_endio_writer_helper() To: linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi Btrfs Developers, I found a potential data race around the disk_i_size in btrfs inodes. Following is the call stack in the helper threads. [Thread 1] btrfs_endio_write_helper normal_work_helper finish_ordered_fn btrfs_finish_ordered_io btrfs_ordered_update_i_size [WRITE] BTRFS_I(inode)->disk_i_size = new_i_size; [Thread 2] btrfs_endio_write_helper normal_work_helper finish_ordered_fn btrfs_finish_ordered_io insert_reserved_file_extent __btrfs_drop_extents [READ] if (start >= BTRFS_I(inode)->disk_i_size && !replace_extent) I can confirm that the read and write may happen in close proximity (in time) and the READ may get either the old value or the new value of the disk_i_size. Is this a valid data race or some operation designed for lock-free accesses? Best Regards, Meng