btrfs: fix condition of commit transaction

Old code bypass commit transaction when we don't have enough
pinned space, but another case is there exist freed bgs in current
transction, it have possibility to make alloc_chunk success.

This patch modify the condition to:
if (have_free_bg || have_pinned_space) commit_transaction()

Confirmed above action by printk before and after patch.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/extent-tree.c

@@ -3857,7 +3857,9 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	u64 used;
-	int ret = 0, committed = 0;
+	int ret = 0;
+	int committed = 0;
+	int have_pinned_space = 1;
 
 	/* make sure bytes are sectorsize aligned */
 	bytes = ALIGN(bytes, root->sectorsize);
@@ -3925,11 +3927,12 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
 
 		/*
 		 * If we don't have enough pinned space to deal with this
-		 * allocation don't bother committing the transaction.
+		 * allocation, and no removed chunk in current transaction,
+		 * don't bother committing the transaction.
 		 */
 		if (percpu_counter_compare(&data_sinfo->total_bytes_pinned,
 					   bytes) < 0)
-			committed = 1;
+			have_pinned_space = 0;
 		spin_unlock(&data_sinfo->lock);
 
 		/* commit the current transaction and try again */
@@ -3941,10 +3944,15 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
 			trans = btrfs_join_transaction(root);
 			if (IS_ERR(trans))
 				return PTR_ERR(trans);
+			if (have_pinned_space ||
+			    trans->transaction->have_free_bgs) {
 				ret = btrfs_commit_transaction(trans, root);
 				if (ret)
 					return ret;
 				goto again;
+			} else {
+				btrfs_end_transaction(trans, root);
+			}
 		}
 
 		trace_btrfs_space_reservation(root->fs_info,