f2fs: reposition unlock_new_inode to prevent accessing invalid inode

As the race condition on the inode cache, following scenario can appear:
[Thread a]				[Thread b]
					->f2fs_mkdir
					  ->f2fs_add_link
					    ->__f2fs_add_link
					      ->init_inode_metadata failed here
->gc_thread_func
  ->f2fs_gc
    ->do_garbage_collect
      ->gc_data_segment
        ->f2fs_iget
          ->iget_locked
            ->wait_on_inode
					  ->unlock_new_inode
        ->move_data_page
					  ->make_bad_inode
					  ->iput

When we fail in create/symlink/mkdir/mknod/tmpfile, the new allocated inode
should be set as bad to avoid being accessed by other thread. But in above
scenario, it allows f2fs to access the invalid inode before this inode was set
as bad.
This patch fix the potential problem, and this issue was found by code review.

change log from v1:
 o Add condition judgment in gc_data_segment() suggested by Changman Lee.
 o use iget_failed to simplify code.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -593,7 +593,7 @@ next_step:
 
 		if (phase == 2) {
 			inode = f2fs_iget(sb, dni.ino);
-			if (IS_ERR(inode))
+			if (IS_ERR(inode) || is_bad_inode(inode))
 				continue;
 
 			start_bidx = start_bidx_of_node(nofs, F2FS_I(inode));

fs/f2fs/namei.c

@@ -134,9 +134,7 @@ static int f2fs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
 	return 0;
 out:
 	clear_nlink(inode);
-	unlock_new_inode(inode);
-	make_bad_inode(inode);
-	iput(inode);
+	iget_failed(inode);
 	alloc_nid_failed(sbi, ino);
 	return err;
 }
@@ -267,9 +265,7 @@ static int f2fs_symlink(struct inode *dir, struct dentry *dentry,
 	return err;
 out:
 	clear_nlink(inode);
-	unlock_new_inode(inode);
-	make_bad_inode(inode);
-	iput(inode);
+	iget_failed(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;
 }
@@ -308,9 +304,7 @@ static int f2fs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 out_fail:
 	clear_inode_flag(F2FS_I(inode), FI_INC_LINK);
 	clear_nlink(inode);
-	unlock_new_inode(inode);
-	make_bad_inode(inode);
-	iput(inode);
+	iget_failed(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;
 }
@@ -354,9 +348,7 @@ static int f2fs_mknod(struct inode *dir, struct dentry *dentry,
 	return 0;
 out:
 	clear_nlink(inode);
-	unlock_new_inode(inode);
-	make_bad_inode(inode);
-	iput(inode);
+	iget_failed(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;
 }
@@ -688,9 +680,7 @@ release_out:
 out:
 	f2fs_unlock_op(sbi);
 	clear_nlink(inode);
-	unlock_new_inode(inode);
-	make_bad_inode(inode);
-	iput(inode);
+	iget_failed(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;
 }