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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 1E482C433E1 for ; Sun, 26 Jul 2020 12:40:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E67F62065E for ; Sun, 26 Jul 2020 12:40:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595767206; bh=YIznru0ivZsPeEx2Y2gG79KDkuZbSAQ/hi64JTOqZ/I=; h=Subject:To:Cc:From:Date:List-ID:From; b=dMXqZWRY/KC304hMC+CdoB0omNbArCo2b2lxuVjQIXyS0P1dEYKDR+Wcnwgnhr3Q1 CrtVrzVLKLmxf1CE1KtFuZ4NGTUcgTrdt5j84vRlCVTy+wRCGZvWDQ1KWVtx5KehUl iq1srXpG4t6gK7ZW4+Tnh5Yo6M6PCsTskMVHNOW0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726042AbgGZMkG (ORCPT ); Sun, 26 Jul 2020 08:40:06 -0400 Received: from wforward2-smtp.messagingengine.com ([64.147.123.31]:55165 "EHLO wforward2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725848AbgGZMkG (ORCPT ); Sun, 26 Jul 2020 08:40:06 -0400 Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailforward.west.internal (Postfix) with ESMTP id 5DC056DC; Sun, 26 Jul 2020 08:40:05 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute1.internal (MEProxy); Sun, 26 Jul 2020 08:40:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:message-id:mime-version:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm3; bh=rlBy47 gdgPahAWt5wAt7EwUU07rOgkSudlgBzrPDkns=; b=gUPR3hDTXlYHEUx/PviXge 2N50BORIkkpswzxH5OxTTxqfZFkzSqhJym0VhzOlvJsKJOh4GjX9LEZ4V+naZEwf BOn9AQOlzeIQhda3xwKZIycbmpamjnfmIR1HVXCl0vJ/xrasJLwAFFoDInfK0nBF iajdGvmq0H6A+/FX74Zc+CnnJuxMnE02AdP74Se5/LBrpWiV28wHW7Z0KjTYVQxN zTxmPVlxfMU6tPIPz95UzwBtN9zL0wk0GBDmjHyIZqPJc6W68Wb6j+2sONhfYLuQ SEbiEzMKxVbLTXFgv8wDv9vdyOo1Vb7PRvPwuz72BnlrAAm994qGwYpepHniYLYg == X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduiedrheejgdehhecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecunecujfgurhepuffvhfffkfggtgfgsehtkeertddttd flnecuhfhrohhmpeeoghhrvghgkhhhsehlihhnuhigfhhouhhnuggrthhiohhnrdhorhhg qeenucggtffrrghtthgvrhhnpeeiteevheeuvdfhtdfgvdeiieehheefleevveehjedute evueevledujeejgfetheenucfkphepkeefrdekiedrkeelrddutdejnecuvehluhhsthgv rhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepghhrvghgsehkrhhorghhrd gtohhm X-ME-Proxy: Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) by mail.messagingengine.com (Postfix) with ESMTPA id 7AE853280063; Sun, 26 Jul 2020 08:40:04 -0400 (EDT) Subject: FAILED: patch "[PATCH] btrfs: fix mount failure caused by race with umount" failed to apply to 4.9-stable tree To: boris@bur.io, dsterba@suse.com Cc: From: Date: Sun, 26 Jul 2020 14:39:59 +0200 Message-ID: <1595767199121103@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 48cfa61b58a1fee0bc49eef04f8ccf31493b7cdd Mon Sep 17 00:00:00 2001 From: Boris Burkov Date: Thu, 16 Jul 2020 13:29:46 -0700 Subject: [PATCH] btrfs: fix mount failure caused by race with umount It is possible to cause a btrfs mount to fail by racing it with a slow umount. The crux of the sequence is generic_shutdown_super not yet calling sop->put_super before btrfs_mount_root calls btrfs_open_devices. If that occurs, btrfs_open_devices will decide the opened counter is non-zero, increment it, and skip resetting fs_devices->total_rw_bytes to 0. From here, mount will call sget which will result in grab_super trying to take the super block umount semaphore. That semaphore will be held by the slow umount, so mount will block. Before up-ing the semaphore, umount will delete the super block, resulting in mount's sget reliably allocating a new one, which causes the mount path to dutifully fill it out, and increment total_rw_bytes a second time, which causes the mount to fail, as we see double the expected bytes. Here is the sequence laid out in greater detail: CPU0 CPU1 down_write sb->s_umount btrfs_kill_super kill_anon_super(sb) generic_shutdown_super(sb); shrink_dcache_for_umount(sb); sync_filesystem(sb); evict_inodes(sb); // SLOW btrfs_mount_root btrfs_scan_one_device fs_devices = device->fs_devices fs_info->fs_devices = fs_devices // fs_devices-opened makes this a no-op btrfs_open_devices(fs_devices, mode, fs_type) s = sget(fs_type, test, set, flags, fs_info); find sb in s_instances grab_super(sb); down_write(&s->s_umount); // blocks sop->put_super(sb) // sb->fs_devices->opened == 2; no-op spin_lock(&sb_lock); hlist_del_init(&sb->s_instances); spin_unlock(&sb_lock); up_write(&sb->s_umount); return 0; retry lookup don't find sb in s_instances (deleted by CPU0) s = alloc_super return s; btrfs_fill_super(s, fs_devices, data) open_ctree // fs_devices total_rw_bytes improperly set! btrfs_read_chunk_tree read_one_dev // increment total_rw_bytes again!! super_total_bytes < fs_devices->total_rw_bytes // ERROR!!! To fix this, we clear total_rw_bytes from within btrfs_read_chunk_tree before the calls to read_one_dev, while holding the sb umount semaphore and the uuid mutex. To reproduce, it is sufficient to dirty a decent number of inodes, then quickly umount and mount. for i in $(seq 0 500) do dd if=/dev/zero of="/mnt/foo/$i" bs=1M count=1 done umount /mnt/foo& mount /mnt/foo does the trick for me. CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Boris Burkov Reviewed-by: David Sterba Signed-off-by: David Sterba diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 0d6e785bcb98..f403fb1e6d37 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -7051,6 +7051,14 @@ int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info) mutex_lock(&uuid_mutex); mutex_lock(&fs_info->chunk_mutex); + /* + * It is possible for mount and umount to race in such a way that + * we execute this code path, but open_fs_devices failed to clear + * total_rw_bytes. We certainly want it cleared before reading the + * device items, so clear it here. + */ + fs_info->fs_devices->total_rw_bytes = 0; + /* * Read all device items, and then all the chunk items. All * device items are found before any chunk item (their object id