f2fs: fix a bug caused by NULL extent tree

Thread A: Thread B:

-f2fs_remount
-sbi->mount_opt.opt = 0;
<--- -f2fs_iget
-do_read_inode
-f2fs_init_extent_tree
-F2FS_I(inode)->extent_tree is NULL
-default_options && parse_options
-remount return
<--- -f2fs_map_blocks
-f2fs_lookup_extent_tree
-f2fs_bug_on(sbi, !et);

The same problem with f2fs_new_inode.

Signed-off-by: Yunlei He <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/extent_cache.c

···
 }
 
 /* return true, if inode page is changed */
-bool f2fs_init_extent_tree(struct inode *inode, struct f2fs_extent *i_ext)
+static bool __f2fs_init_extent_tree(struct inode *inode, struct f2fs_extent *i_ext)
 {
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct extent_tree *et;
···
 out:
 	write_unlock(&et->lock);
 	return false;
+}
+
+bool f2fs_init_extent_tree(struct inode *inode, struct f2fs_extent *i_ext)
+{
+	bool ret =  __f2fs_init_extent_tree(inode, i_ext);
+
+	if (!F2FS_I(inode)->extent_tree)
+		set_inode_flag(inode, FI_NO_EXTENT);
+
+	return ret;
 }
 
 static bool f2fs_lookup_extent_tree(struct inode *inode, pgoff_t pgofs,