f2fs: fix to check return value of f2fs_do_truncate_blocks()

Otherwise, if truncation on cow_inode failed, remained data may
pollute current transaction of atomic write.

Cc: Daeho Jeong <daehojeong@google.com>
Fixes: a46bebd5 ("f2fs: synchronize atomic write aborts")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -2113,7 +2113,11 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 		clear_inode_flag(fi->cow_inode, FI_INLINE_DATA);
 	} else {
 		/* Reuse the already created COW inode */
-		f2fs_do_truncate_blocks(fi->cow_inode, 0, true);
+		ret = f2fs_do_truncate_blocks(fi->cow_inode, 0, true);
+		if (ret) {
+			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
+			goto out;
+		}
 	}
 
 	f2fs_write_inode(inode, NULL);