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=-10.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,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 79631C43387 for ; Mon, 7 Jan 2019 12:44:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38F8B2183E for ; Mon, 7 Jan 2019 12:44:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546865070; bh=VLu3TFiQ0KNuDmcWLcBjOfsecM8mEB22snLI2mFtYeM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ebYq6hfTUp2FLetn3AXfZEj5zUy+iBxDb9VlVnPbeSHsgKkFinf2/djsczep7cK91 rl0eif9uLZyD/uvFgQlzpHcUPKFa6Hc+lCSzNSWmnXfalSR8yaFRBr8F40e6ddDQJb zZSikk0WU+8nC7F85HLGOuhYORxGLbhiBoIejU/c= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728276AbfAGMo3 (ORCPT ); Mon, 7 Jan 2019 07:44:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:32924 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727324AbfAGMo0 (ORCPT ); Mon, 7 Jan 2019 07:44:26 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 84D9D2177B; Mon, 7 Jan 2019 12:44:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546865065; bh=VLu3TFiQ0KNuDmcWLcBjOfsecM8mEB22snLI2mFtYeM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WxXWRBj8qRHrAUWhXJf+M6aflW5gaFoE/kKwR/97eTiFPoX7aWHK6Y1TaA4mUyrvz AGVCme88K9ZeXegj/H4ppvA9cnoqWRDCmZH7HN/9EUfFXgNZvUoLbzpIkE4mRctLcC sixdK4R67eQo41uTNdaodAlV5HbUx1A2NKxAAzqg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Filipe Manana , David Sterba Subject: [PATCH 4.20 098/145] Btrfs: send, fix race with transaction commits that create snapshots Date: Mon, 7 Jan 2019 13:32:15 +0100 Message-Id: <20190107104450.053435515@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190107104437.308206189@linuxfoundation.org> References: <20190107104437.308206189@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ From: Filipe Manana commit be6821f82c3cc36e026f5afd10249988852b35ea upstream. If we create a snapshot of a snapshot currently being used by a send operation, we can end up with send failing unexpectedly (returning -ENOENT error to user space for example). The following diagram shows how this happens. CPU 1 CPU2 CPU3 btrfs_ioctl_send() (...) create_snapshot() -> creates snapshot of a root used by the send task btrfs_commit_transaction() create_pending_snapshot() __get_inode_info() btrfs_search_slot() btrfs_search_slot_get_root() down_read commit_root_sem get reference on eb of the commit root -> eb with bytenr == X up_read commit_root_sem btrfs_cow_block(root node) btrfs_free_tree_block() -> creates delayed ref to free the extent btrfs_run_delayed_refs() -> runs the delayed ref, adds extent to fs_info->pinned_extents btrfs_finish_extent_commit() unpin_extent_range() -> marks extent as free in the free space cache transaction commit finishes btrfs_start_transaction() (...) btrfs_cow_block() btrfs_alloc_tree_block() btrfs_reserve_extent() -> allocates extent at bytenr == X btrfs_init_new_buffer(bytenr X) btrfs_find_create_tree_block() alloc_extent_buffer(bytenr X) find_extent_buffer(bytenr X) -> returns existing eb, which the send task got (...) -> modifies content of the eb with bytenr == X -> uses an eb that now belongs to some other tree and no more matches the commit root of the snapshot, resuts will be unpredictable The consequences of this race can be various, and can lead to searches in the commit root performed by the send task failing unexpectedly (unable to find inode items, returning -ENOENT to user space, for example) or not failing because an inode item with the same number was added to the tree that reused the metadata extent, in which case send can behave incorrectly in the worst case or just fail later for some reason. Fix this by performing a copy of the commit root's extent buffer when doing a search in the context of a send operation. CC: stable@vger.kernel.org # 4.4.x: 1fc28d8e2e9: Btrfs: move get root out of btrfs_search_slot to a helper CC: stable@vger.kernel.org # 4.4.x: f9ddfd0592a: Btrfs: remove unused check of skip_locking CC: stable@vger.kernel.org # 4.4.x Signed-off-by: Filipe Manana Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/ctree.c | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 deletions(-) --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -2584,14 +2584,27 @@ static struct extent_buffer *btrfs_searc root_lock = BTRFS_READ_LOCK; if (p->search_commit_root) { - /* The commit roots are read only so we always do read locks */ - if (p->need_commit_sem) + /* + * The commit roots are read only so we always do read locks, + * and we always must hold the commit_root_sem when doing + * searches on them, the only exception is send where we don't + * want to block transaction commits for a long time, so + * we need to clone the commit root in order to avoid races + * with transaction commits that create a snapshot of one of + * the roots used by a send operation. + */ + if (p->need_commit_sem) { down_read(&fs_info->commit_root_sem); - b = root->commit_root; - extent_buffer_get(b); - level = btrfs_header_level(b); - if (p->need_commit_sem) + b = btrfs_clone_extent_buffer(root->commit_root); up_read(&fs_info->commit_root_sem); + if (!b) + return ERR_PTR(-ENOMEM); + + } else { + b = root->commit_root; + extent_buffer_get(b); + } + level = btrfs_header_level(b); /* * Ensure that all callers have set skip_locking when * p->search_commit_root = 1. @@ -2717,6 +2730,10 @@ int btrfs_search_slot(struct btrfs_trans again: prev_cmp = -1; b = btrfs_search_slot_get_root(root, p, write_lock_level); + if (IS_ERR(b)) { + ret = PTR_ERR(b); + goto done; + } while (b) { level = btrfs_header_level(b);