From patchwork Fri Apr 17 16:43:51 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Filipe Manana X-Patchwork-Id: 6234871 Return-Path: X-Original-To: patchwork-linux-btrfs@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 2459E9F1AC for ; Fri, 17 Apr 2015 16:48:14 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 26427203AC for ; Fri, 17 Apr 2015 16:48:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDCCA20397 for ; Fri, 17 Apr 2015 16:48:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932585AbbDQQr7 (ORCPT ); Fri, 17 Apr 2015 12:47:59 -0400 Received: from victor.provo.novell.com ([137.65.250.26]:51759 "EHLO prv3-mh.provo.novell.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753608AbbDQQr6 (ORCPT ); Fri, 17 Apr 2015 12:47:58 -0400 Received: from debian3.lan (prv-ext-foundry1int.gns.novell.com [137.65.251.240]) by prv3-mh.provo.novell.com with ESMTP (NOT encrypted); Fri, 17 Apr 2015 10:47:52 -0600 From: Filipe Manana To: linux-btrfs@vger.kernel.org Cc: Filipe Manana , Subject: [PATCH] Btrfs: fix data loss after concurrent fsyncs for files in the same subvol Date: Fri, 17 Apr 2015 17:43:51 +0100 Message-Id: <1429289031-1088-1-git-send-email-fdmanana@suse.com> X-Mailer: git-send-email 2.1.3 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_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 If we have concurrent fsync calls against files living in the same subvolume, we have some time window where we don't add the collected ordered extents to the running transaction's list of ordered extents and return success to userspace. This can result in data loss if the ordered extents complete after the current transaction commits and a power failure happens after the current transaction commits and before the next one commits. A sequence of steps that lead to this: CPU 0 CPU 1 btrfs_sync_file(inode A) btrfs_sync_file(inode B) btrfs_log_inode_parent() btrfs_log_inode_parent() start_log_trans() lock root->log_mutex ctx->log_transid = root->log_transid = N unlock root->log_mutex start_log_trans() lock root->log_mutex ctx->log_transid = root->log_transid = N unlock root->log_mutex btrfs_log_inode() btrfs_log_inode() btrfs_get_logged_extents() btrfs_get_logged_extents() --> gets orderede extent A -> gets ordered extent B into local list logged_list into local list logged_list write items into the log tree write items into the log tree btrfs_submit_logged_extents(&logged_list) --> splices logged_list into log_root->logged_list[N % 2] (N == log_root->log_transid) btrfs_sync_log() lock root->log_mutex atomic_set(&root->log_commit[N % 2], 1) (N == ctx->log_transid) btrfs_write_marked_extents() root->log_transid++ --> becomes N + 1 log_root->log_transid = root->log_transid unlock root->log_mutex btrfs_submit_logged_extents(&logged_list) --> splices logged_list into log_root->logged_list[(N + 1) % 2] (N + 1 == log_root->log_transid) btrfs_sync_log() lock root->log_mutex atomic_read(&root->log_commit[N % 2]) == 1 (N == ctx->log_transid) wait on root->log_commit_wait[N % 2] (where N == ctx->log_transid) for atomic_read(&root->log_commit[N % 2] == 0 and root->log_transid_committed == N btrfs_wait_marked_extents() btrfs_wait_logged_extents() --> adds ordered extents from log_root->logged_list[N % 2] to the trans->ordered list (N == ctx->log_transid) write_ctree_super() lock root->log_mutex root->log_transid_committed++; --> becomes N unlock root->log_mutex wake_up(&root->log_commit_wait[N % 2]) (N == ctx->log_transid) btrfs_sync_file(inode A) returns 0 to userspace wakes up from root->log_commit_wait[N % 2] returns 0 from btrfs_sync_log() immediately btrfs_sync_file(inode B) returns 0 to userspace some time later current transaction commit starts waits for ordered extent A to complete transaction commit finishes ********* power failure ************ ordered extent B completes (updates subvol and csum trees) Fix this by ensuring that we add the collected ordered extents into the current transaction's ordered list if when syncing the log we return early because we found our log transaction was already committed or we end up waiting for a matching log transaction commit that is ongoing to complete. CC: # 3.18+ Signed-off-by: Filipe Manana --- fs/btrfs/ordered-data.c | 3 ++- fs/btrfs/tree-log.c | 4 ++++ 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c index 72b6f0d..7005eb7 100644 --- a/fs/btrfs/ordered-data.c +++ b/fs/btrfs/ordered-data.c @@ -509,7 +509,8 @@ void btrfs_wait_logged_extents(struct btrfs_trans_handle *trans, wait_event(ordered->wait, test_bit(BTRFS_ORDERED_IO_DONE, &ordered->flags)); - list_add_tail(&ordered->trans_list, &trans->ordered); + if (list_empty(&ordered->trans_list)) + list_add_tail(&ordered->trans_list, &trans->ordered); spin_lock_irq(&log->log_extents_lock[index]); } spin_unlock_irq(&log->log_extents_lock[index]); diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 2fd95a7..64447b9 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -2635,6 +2635,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, log_transid = ctx->log_transid; if (root->log_transid_committed >= log_transid) { mutex_unlock(&root->log_mutex); + if (ctx->log_ret == 0) + btrfs_wait_logged_extents(trans, log, log_transid); return ctx->log_ret; } @@ -2642,6 +2644,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, if (atomic_read(&root->log_commit[index1])) { wait_log_commit(trans, root, log_transid); mutex_unlock(&root->log_mutex); + if (ctx->log_ret == 0) + btrfs_wait_logged_extents(trans, log, log_transid); return ctx->log_ret; } ASSERT(log_transid == root->log_transid);