From patchwork Wed Aug 12 14:44:51 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Filipe Manana X-Patchwork-Id: 7002251 Return-Path: X-Original-To: patchwork-linux-btrfs@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 7956EC05AC for ; Wed, 12 Aug 2015 14:45:09 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id F06ED2064F for ; Wed, 12 Aug 2015 14:45:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0748A20652 for ; Wed, 12 Aug 2015 14:45:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932226AbbHLOpA (ORCPT ); Wed, 12 Aug 2015 10:45:00 -0400 Received: from mail.kernel.org ([198.145.29.136]:57510 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753199AbbHLOo7 (ORCPT ); Wed, 12 Aug 2015 10:44:59 -0400 Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 2257620652; Wed, 12 Aug 2015 14:44:58 +0000 (UTC) Received: from debian3.lan (bl13-153-166.dsl.telepac.pt [85.246.153.166]) (using TLSv1.2 with cipher AES128-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 94AD72064F; Wed, 12 Aug 2015 14:44:56 +0000 (UTC) From: fdmanana@kernel.org To: linux-btrfs@vger.kernel.org Cc: Filipe Manana , stable@vger.kernel.org Subject: [PATCH v2] Btrfs: check if previous transaction aborted to avoid fs corruption Date: Wed, 12 Aug 2015 15:44:51 +0100 Message-Id: <1439390691-5451-1-git-send-email-fdmanana@kernel.org> X-Mailer: git-send-email 2.1.3 In-Reply-To: <1439388661-5316-1-git-send-email-fdmanana@kernel.org> References: <1439388661-5316-1-git-send-email-fdmanana@kernel.org> X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Filipe Manana While we are committing a transaction, it's possible the previous one is still finishing its commit and therefore we wait for it to finish first. However we were not checking if that previous transaction ended up getting aborted after we waited for it to commit, so we ended up committing the current transaction which can lead to fs corruption because the new superblock can point to trees that have had one or more nodes/leafs that were never durably persisted. The following sequence diagram exemplifies how this is possible: CPU 0 CPU 1 transaction N starts (...) btrfs_commit_transaction(N) cur_trans->state = TRANS_STATE_COMMIT_START; (...) cur_trans->state = TRANS_STATE_COMMIT_DOING; (...) cur_trans->state = TRANS_STATE_UNBLOCKED; root->fs_info->running_transaction = NULL; btrfs_start_transaction() --> starts transaction N + 1 btrfs_write_and_wait_transaction(trans, root); --> starts writing all new or COWed ebs created at transaction N creates some new ebs, COWs some existing ebs but doesn't COW or deletes eb X btrfs_commit_transaction(N + 1) (...) cur_trans->state = TRANS_STATE_COMMIT_START; (...) wait_for_commit(root, prev_trans); --> prev_trans == transaction N btrfs_write_and_wait_transaction() continues writing ebs --> fails writing eb X, we abort transaction N and set bit BTRFS_FS_STATE_ERROR on fs_info->fs_state, so no new transactions can start after setting that bit cleanup_transaction() btrfs_cleanup_one_transaction() wakes up task at CPU 1 continues, doesn't abort because cur_trans->aborted (transaction N + 1) is zero, and no checks for bit BTRFS_FS_STATE_ERROR in fs_info->fs_state are made btrfs_write_and_wait_transaction(trans, root); --> succeeds, no errors during writeback write_ctree_super(trans, root, 0); --> succeeds --> we have now a superblock that points us to some root that uses eb X, which was never written to disk In this scenario future attempts to read eb X from disk results in an error message like "parent transid verify failed on X wanted Y found Z". So fix this by aborting the current transaction if after waiting for the previous transaction we verify that it was aborted. Cc: stable@vger.kernel.org Signed-off-by: Filipe Manana Reviewed-by: Josef Bacik Reviewed-by: Liu Bo --- V2: Added missing cc to stable and included Josef's reviewed-by tag. No code changes. fs/btrfs/transaction.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 51e0f0d..d15a43f 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -1893,8 +1893,11 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, spin_unlock(&root->fs_info->trans_lock); wait_for_commit(root, prev_trans); + ret = prev_trans->aborted; btrfs_put_transaction(prev_trans); + if (ret) + goto cleanup_transaction; } else { spin_unlock(&root->fs_info->trans_lock); }