--- /dev/null
+From dad48e73127ba10279ea33e6dbc8d3905c4d31c0 Mon Sep 17 00:00:00 2001
+From: Yunlei He <heyunlei@huawei.com>
+Date: Fri, 19 May 2017 15:06:12 +0800
+Subject: f2fs: fix a bug caused by NULL extent tree
+
+From: Yunlei He <heyunlei@huawei.com>
+
+commit dad48e73127ba10279ea33e6dbc8d3905c4d31c0 upstream.
+
+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 <heyunlei@huawei.com>
+Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
+Signed-off-by: Nikolay Borisov <nborisov@suse.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/f2fs/extent_cache.c | 12 +++++++++++-
+ 1 file changed, 11 insertions(+), 1 deletion(-)
+
+--- a/fs/f2fs/extent_cache.c
++++ b/fs/f2fs/extent_cache.c
+@@ -177,7 +177,7 @@ static void __drop_largest_extent(struct
+ }
+
+ /* 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;
+@@ -215,6 +215,16 @@ out:
+ 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,
+ struct extent_info *ei)
+ {