Btrfs: fix EDQUOT handling in btrfs_delalloc_reserve_metadata

When btrfs_qgroup_reserve returned a failure, we were missing a counter
operation for BTRFS_I(inode)->outstanding_extents++, leading to warning
messages about outstanding extents and space_info->bytes_may_use != 0.
Additionally, the error handling code didn't take into account that we
dropped the inode lock which might require more cleanup.

Luckily, all the cleanup code we need is already there and can be shared
with reserve_metadata_bytes, which is exactly what this patch does.
Reported-by: Lev Vainblat <lev@zadarastorage.com>
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/extent-tree.c

@@ -4534,7 +4534,7 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
 	unsigned nr_extents = 0;
 	int extra_reserve = 0;
 	enum btrfs_reserve_flush_enum flush = BTRFS_RESERVE_FLUSH_ALL;
-	int ret;
+	int ret = 0;
 	bool delalloc_lock = true;
 
 	/* If we are a free space inode we need to not flush since we will be in
@@ -4579,20 +4579,18 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
 	csum_bytes = BTRFS_I(inode)->csum_bytes;
 	spin_unlock(&BTRFS_I(inode)->lock);
 
-	if (root->fs_info->quota_enabled) {
+	if (root->fs_info->quota_enabled)
 		ret = btrfs_qgroup_reserve(root, num_bytes +
 					   nr_extents * root->leafsize);
-		if (ret) {
-			spin_lock(&BTRFS_I(inode)->lock);
-			calc_csum_metadata_size(inode, num_bytes, 0);
-			spin_unlock(&BTRFS_I(inode)->lock);
-			if (delalloc_lock)
-				mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);
-			return ret;
-		}
-	}
 
-	ret = reserve_metadata_bytes(root, block_rsv, to_reserve, flush);
+	/*
+	 * ret != 0 here means the qgroup reservation failed, we go straight to
+	 * the shared error handling then.
+	 */
+	if (ret == 0)
+		ret = reserve_metadata_bytes(root, block_rsv,
+					     to_reserve, flush);
+
 	if (ret) {
 		u64 to_free = 0;
 		unsigned dropped;