[PATCH 2/2] f2fs: fix to check extent cache in f2fs_drop_extent_tree

[Chao Yu]

If noextent_cache mount option is on, we will never initialize extent tree
in inode, but still we're going to access it in f2fs_drop_extent_tree,
result in kernel panic as below:

 BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
 IP: _raw_write_lock+0xc/0x30
 Call Trace:
  ? f2fs_drop_extent_tree+0x41/0x70 [f2fs]
  f2fs_fallocate+0x5a0/0xdd0 [f2fs]
  ? common_file_perm+0x47/0xc0
  ? apparmor_file_permission+0x1a/0x20
  vfs_fallocate+0x15b/0x290
  SyS_fallocate+0x44/0x70
  do_syscall_64+0x6e/0x160
  entry_SYSCALL64_slow_path+0x25/0x25

This patch fixes to check extent cache status before using in
f2fs_drop_extent_tree.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 fs/f2fs/extent_cache.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index ff2352a0ed15..aff6c2ed1c02 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -706,6 +706,9 @@ void f2fs_drop_extent_tree(struct inode *inode)
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct extent_tree *et = F2FS_I(inode)->extent_tree;
 
+	if (!f2fs_may_extent_tree(inode))
+		return;
+
 	set_inode_flag(inode, FI_NO_EXTENT);
 
 	write_lock(&et->lock);
-- 
2.15.0.55.gc2ece9dc4de6