f2fs: fix race conditon on truncation with inline_data

f2fs: fix race conditon on truncation with inline_data

Let's consider the following scenario.

blkaddr[0] inline_data i_size  i_blocks writepage           truncate
  NEW        X        4096        2    dirty page #0
  NEW        X         0                                    change i_size
  NEW        X         0          2    f2fs_write_inline_data
  NEW        X         0          2    get_dnode_of_data
  NEW        X         0          2    truncate_data_blocks_range
  NULL       O         0          1    memcpy(inline_data)
  NULL       O         0          1    f2fs_put_dnode
  NULL       O         0          1                         f2fs_truncate
  NULL       O         0          1                         get_dnode_of_data
  NULL       O         0          1                       *invalid block addr*

This patch adds checking inline_data flag during f2fs_truncate not to refer
corrupted block indices.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>