From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp1040.oracle.com ([156.151.31.81]:39091 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754754AbbJ1F04 (ORCPT ); Wed, 28 Oct 2015 01:26:56 -0400 From: Sasha Levin To: stable@vger.kernel.org, stable-commits@vger.kernel.org Cc: Filipe Manana , Chris Mason , Sasha Levin Subject: [added to the 3.18 stable tree] Btrfs: check if previous transaction aborted to avoid fs corruption Date: Wed, 28 Oct 2015 01:21:57 -0400 Message-Id: <1446009925-26739-21-git-send-email-sasha.levin@oracle.com> In-Reply-To: <1446009925-26739-1-git-send-email-sasha.levin@oracle.com> References: <1446009925-26739-1-git-send-email-sasha.levin@oracle.com> Sender: stable-owner@vger.kernel.org List-ID: From: Filipe Manana This patch has been added to the 3.18 stable tree. If you have any objections, please let us know. =============== [ Upstream commit 1f9b8c8fbc9a4d029760b16f477b9d15500e3a34 ] 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 Signed-off-by: Chris Mason Signed-off-by: Sasha Levin --- fs/btrfs/transaction.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 63c6d05..7dce00b 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -1756,8 +1756,11 @@ 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); } -- 2.1.4