Merge upstream-f2fs-stable-linux-4.9.y into android-4.9

Merge upstream-f2fs-stable-linux-4.9.y into android-4.9

* origin/upstream-f2fs-stable-linux-4.9.y:
  f2fs: fix to avoid accessing xattr across the boundary
  f2fs: fix to avoid potential race on sbi->unusable_block_count access/update
  f2fs: add tracepoint for f2fs_filemap_fault()
  f2fs: introduce DATA_GENERIC_ENHANCE
  f2fs: fix to handle error in f2fs_disable_checkpoint()
  f2fs: remove redundant check in f2fs_file_write_iter()
  f2fs: fix to be aware of readonly device in write_checkpoint()
  f2fs: fix to skip recovery on readonly device
  f2fs: fix to consider multiple device for readonly check
  f2fs: relocate chksum_offset for large_nat_bitmap feature
  f2fs: allow unfixed f2fs_checkpoint.checksum_offset
  f2fs: Replace spaces with tab
  f2fs: insert space before the open parenthesis '('
  f2fs: allow address pointer number of dnode aligning to specified size
  f2fs: introduce f2fs_read_single_page() for cleanup
  f2fs: mark is_extension_exist() inline
  f2fs: fix to set FI_UPDATE_WRITE correctly
  f2fs: fix to avoid panic in f2fs_inplace_write_data()
  f2fs: fix to do sanity check on valid block count of segment
  f2fs: fix to do sanity check on valid node/block count
  f2fs: fix to avoid panic in do_recover_data()
  f2fs: fix to do sanity check on free nid
  f2fs: fix to do checksum even if inode page is uptodate
  f2fs: fix to avoid panic in f2fs_remove_inode_page()
  f2fs: fix to clear dirty inode in error path of f2fs_iget()
  f2fs: remove new blank line of f2fs kernel message
  f2fs: fix wrong __is_meta_io() macro
  f2fs: fix to avoid panic in dec_valid_node_count()
  f2fs: fix to avoid panic in dec_valid_block_count()
  f2fs: fix to use inline space only if inline_xattr is enable
  f2fs: fix to retrieve inline xattr space
  f2fs: fix error path of recovery
  f2fs: fix to avoid deadloop in foreground GC
  f2fs: data: fix warning Using plain integer as NULL pointer
  f2fs: add tracepoint for f2fs_file_write_iter()
  f2fs: add comment for conditional compilation statement
  f2fs: fix potential recursive call when enabling data_flush
  f2fs: improve discard handling with multi-device volumes
  f2fs: Reduce zoned block device memory usage
  f2fs: Fix use of number of devices

Change-Id: I5df9e9906428ef2eb852838ec4f598599e0e5c63
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>