Btrfs: sync log after logging new name

When we add a new name for an inode which was logged in the current
transaction, we update the inode in the log so that its new name and
ancestors are added to the log. However when we do this we do not persist
the log, so the changes remain in memory only, and as a consequence, any
ancestors that were created in the current transaction are updated such
that future calls to btrfs_inode_in_log() return true. This leads to a
subsequent fsync against such new ancestor directories returning
immediately, without persisting the log, therefore after a power failure
the new ancestor directories do not exist, despite fsync being called
against them explicitly.

Example:

  $ mkfs.btrfs -f /dev/sdb
  $ mount /dev/sdb /mnt

  $ mkdir /mnt/A
  $ mkdir /mnt/B
  $ mkdir /mnt/A/C
  $ touch /mnt/B/foo
  $ xfs_io -c "fsync" /mnt/B/foo
  $ ln /mnt/B/foo /mnt/A/C/foo
  $ xfs_io -c "fsync" /mnt/A
  <power failure>

After the power failure, directory "A" does not exist, despite the explicit
fsync on it.

Instead of fixing this by changing the behaviour of the explicit fsync on
directory "A" to persist the log instead of doing nothing, make the logging
of the new file name (which happens when creating a hard link or renaming)
persist the log. This approach not only is simpler, not requiring addition
of new fields to the inode in memory structure, but also gives us the same
behaviour as ext4, xfs and f2fs (possibly other filesystems too).

A test case for fstests follows soon.

Fixes: 12fcfd2 ("Btrfs: tree logging unlink/rename fixes")
Reported-by: Vijay Chidambaram <[email protected]>
Signed-off-by: Filipe Manana <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: fdmanana

fs/btrfs/inode.c

@@ -6634,6 +6634,8 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
 		drop_inode = 1;
 	} else {
 		struct dentry *parent = dentry->d_parent;
+		int ret;
+
 		err = btrfs_update_inode(trans, root, inode);
 		if (err)
 			goto fail;
@@ -6647,7 +6649,12 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
 				goto fail;
 		}
 		d_instantiate(dentry, inode);
-		btrfs_log_new_name(trans, BTRFS_I(inode), NULL, parent);
+		ret = btrfs_log_new_name(trans, BTRFS_I(inode), NULL, parent,
+					 true, NULL);
+		if (ret == BTRFS_NEED_TRANS_COMMIT) {
+			err = btrfs_commit_transaction(trans);
+			trans = NULL;
+		}
 	}
 
 fail:
@@ -9386,14 +9393,21 @@ static int btrfs_rename_exchange(struct inode *old_dir,
 	u64 new_idx = 0;
 	u64 root_objectid;
 	int ret;
-	int ret2;
 	bool root_log_pinned = false;
 	bool dest_log_pinned = false;
+	struct btrfs_log_ctx ctx_root;
+	struct btrfs_log_ctx ctx_dest;
+	bool sync_log_root = false;
+	bool sync_log_dest = false;
+	bool commit_transaction = false;
 
 	/* we only allow rename subvolume link between subvolumes */
 	if (old_ino != BTRFS_FIRST_FREE_OBJECTID && root != dest)
 		return -EXDEV;
 
+	btrfs_init_log_ctx(&ctx_root, old_inode);
+	btrfs_init_log_ctx(&ctx_dest, new_inode);
+
 	/* close the race window with snapshot create/destroy ioctl */
 	if (old_ino == BTRFS_FIRST_FREE_OBJECTID)
 		down_read(&fs_info->subvol_sem);
@@ -9540,15 +9554,29 @@ static int btrfs_rename_exchange(struct inode *old_dir,
 
 	if (root_log_pinned) {
 		parent = new_dentry->d_parent;
-		btrfs_log_new_name(trans, BTRFS_I(old_inode), BTRFS_I(old_dir),
-				parent);
+		ret = btrfs_log_new_name(trans, BTRFS_I(old_inode),
+					 BTRFS_I(old_dir), parent,
+					 false, &ctx_root);
+		if (ret == BTRFS_NEED_LOG_SYNC)
+			sync_log_root = true;
+		else if (ret == BTRFS_NEED_TRANS_COMMIT)
+			commit_transaction = true;
+		ret = 0;
 		btrfs_end_log_trans(root);
 		root_log_pinned = false;
 	}
 	if (dest_log_pinned) {
-		parent = old_dentry->d_parent;
-		btrfs_log_new_name(trans, BTRFS_I(new_inode), BTRFS_I(new_dir),
-				parent);
+		if (!commit_transaction) {
+			parent = old_dentry->d_parent;
+			ret = btrfs_log_new_name(trans, BTRFS_I(new_inode),
+						 BTRFS_I(new_dir), parent,
+						 false, &ctx_dest);
+			if (ret == BTRFS_NEED_LOG_SYNC)
+				sync_log_dest = true;
+			else if (ret == BTRFS_NEED_TRANS_COMMIT)
+				commit_transaction = true;
+			ret = 0;
+		}
 		btrfs_end_log_trans(dest);
 		dest_log_pinned = false;
 	}
@@ -9581,8 +9609,26 @@ static int btrfs_rename_exchange(struct inode *old_dir,
 			dest_log_pinned = false;
 		}
 	}
-	ret2 = btrfs_end_transaction(trans);
-	ret = ret ? ret : ret2;
+	if (!ret && sync_log_root && !commit_transaction) {
+		ret = btrfs_sync_log(trans, BTRFS_I(old_inode)->root,
+				     &ctx_root);
+		if (ret)
+			commit_transaction = true;
+	}
+	if (!ret && sync_log_dest && !commit_transaction) {
+		ret = btrfs_sync_log(trans, BTRFS_I(new_inode)->root,
+				     &ctx_dest);
+		if (ret)
+			commit_transaction = true;
+	}
+	if (commit_transaction) {
+		ret = btrfs_commit_transaction(trans);
+	} else {
+		int ret2;
+
+		ret2 = btrfs_end_transaction(trans);
+		ret = ret ? ret : ret2;
+	}
 out_notrans:
 	if (new_ino == BTRFS_FIRST_FREE_OBJECTID)
 		up_read(&fs_info->subvol_sem);
@@ -9659,6 +9705,9 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	int ret;
 	u64 old_ino = btrfs_ino(BTRFS_I(old_inode));
 	bool log_pinned = false;
+	struct btrfs_log_ctx ctx;
+	bool sync_log = false;
+	bool commit_transaction = false;
 
 	if (btrfs_ino(BTRFS_I(new_dir)) == BTRFS_EMPTY_SUBVOL_DIR_OBJECTID)
 		return -EPERM;
@@ -9816,8 +9865,15 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	if (log_pinned) {
 		struct dentry *parent = new_dentry->d_parent;
 
-		btrfs_log_new_name(trans, BTRFS_I(old_inode), BTRFS_I(old_dir),
-				parent);
+		btrfs_init_log_ctx(&ctx, old_inode);
+		ret = btrfs_log_new_name(trans, BTRFS_I(old_inode),
+					 BTRFS_I(old_dir), parent,
+					 false, &ctx);
+		if (ret == BTRFS_NEED_LOG_SYNC)
+			sync_log = true;
+		else if (ret == BTRFS_NEED_TRANS_COMMIT)
+			commit_transaction = true;
+		ret = 0;
 		btrfs_end_log_trans(root);
 		log_pinned = false;
 	}
@@ -9854,7 +9910,19 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 		btrfs_end_log_trans(root);
 		log_pinned = false;
 	}
-	btrfs_end_transaction(trans);
+	if (!ret && sync_log) {
+		ret = btrfs_sync_log(trans, BTRFS_I(old_inode)->root, &ctx);
+		if (ret)
+			commit_transaction = true;
+	}
+	if (commit_transaction) {
+		ret = btrfs_commit_transaction(trans);
+	} else {
+		int ret2;
+
+		ret2 = btrfs_end_transaction(trans);
+		ret = ret ? ret : ret2;
+	}
 out_notrans:
 	if (old_ino == BTRFS_FIRST_FREE_OBJECTID)
 		up_read(&fs_info->subvol_sem);

fs/btrfs/tree-log.c

@@ -6025,14 +6025,25 @@ void btrfs_record_snapshot_destroy(struct btrfs_trans_handle *trans,
  * Call this after adding a new name for a file and it will properly
  * update the log to reflect the new name.
  *
- * It will return zero if all goes well, and it will return 1 if a
- * full transaction commit is required.
+ * @ctx can not be NULL when @sync_log is false, and should be NULL when it's
+ * true (because it's not used).
+ *
+ * Return value depends on whether @sync_log is true or false.
+ * When true: returns BTRFS_NEED_TRANS_COMMIT if the transaction needs to be
+ *            committed by the caller, and BTRFS_DONT_NEED_TRANS_COMMIT
+ *            otherwise.
+ * When false: returns BTRFS_DONT_NEED_LOG_SYNC if the caller does not need to
+ *             to sync the log, BTRFS_NEED_LOG_SYNC if it needs to sync the log,
+ *             or BTRFS_NEED_TRANS_COMMIT if the transaction needs to be
+ *             committed (without attempting to sync the log).
  */
 int btrfs_log_new_name(struct btrfs_trans_handle *trans,
 			struct btrfs_inode *inode, struct btrfs_inode *old_dir,
-			struct dentry *parent)
+			struct dentry *parent,
+			bool sync_log, struct btrfs_log_ctx *ctx)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
+	int ret;
 
 	/*
 	 * this will force the logging code to walk the dentry chain
@@ -6047,9 +6058,34 @@ int btrfs_log_new_name(struct btrfs_trans_handle *trans,
 	 */
 	if (inode->logged_trans <= fs_info->last_trans_committed &&
 	    (!old_dir || old_dir->logged_trans <= fs_info->last_trans_committed))
-		return 0;
+		return sync_log ? BTRFS_DONT_NEED_TRANS_COMMIT :
+			BTRFS_DONT_NEED_LOG_SYNC;
+
+	if (sync_log) {
+		struct btrfs_log_ctx ctx2;
+
+		btrfs_init_log_ctx(&ctx2, &inode->vfs_inode);
+		ret = btrfs_log_inode_parent(trans, inode, parent, 0, LLONG_MAX,
+					     LOG_INODE_EXISTS, &ctx2);
+		if (ret == BTRFS_NO_LOG_SYNC)
+			return BTRFS_DONT_NEED_TRANS_COMMIT;
+		else if (ret)
+			return BTRFS_NEED_TRANS_COMMIT;
+
+		ret = btrfs_sync_log(trans, inode->root, &ctx2);
+		if (ret)
+			return BTRFS_NEED_TRANS_COMMIT;
+		return BTRFS_DONT_NEED_TRANS_COMMIT;
+	}
+
+	ASSERT(ctx);
+	ret = btrfs_log_inode_parent(trans, inode, parent, 0, LLONG_MAX,
+				     LOG_INODE_EXISTS, ctx);
+	if (ret == BTRFS_NO_LOG_SYNC)
+		return BTRFS_DONT_NEED_LOG_SYNC;
+	else if (ret)
+		return BTRFS_NEED_TRANS_COMMIT;
 
-	return btrfs_log_inode_parent(trans, inode, parent, 0, LLONG_MAX,
-				      LOG_INODE_EXISTS, NULL);
+	return BTRFS_NEED_LOG_SYNC;
 }
 

fs/btrfs/tree-log.h

@@ -71,8 +71,16 @@ void btrfs_record_unlink_dir(struct btrfs_trans_handle *trans,
 			     int for_rename);
 void btrfs_record_snapshot_destroy(struct btrfs_trans_handle *trans,
 				   struct btrfs_inode *dir);
+/* Return values for btrfs_log_new_name() */
+enum {
+	BTRFS_DONT_NEED_TRANS_COMMIT,
+	BTRFS_NEED_TRANS_COMMIT,
+	BTRFS_DONT_NEED_LOG_SYNC,
+	BTRFS_NEED_LOG_SYNC,
+};
 int btrfs_log_new_name(struct btrfs_trans_handle *trans,
 			struct btrfs_inode *inode, struct btrfs_inode *old_dir,
-			struct dentry *parent);
+			struct dentry *parent,
+			bool sync_log, struct btrfs_log_ctx *ctx);
 
 #endif