readahead: fix NULL filp dereference
readahead: fix NULL filp dereference

btrfs relocate_file_extent_cluster() calls us with NULL filp:

  [ 4005.426805] BUG: unable to handle kernel NULL pointer dereference at 00000021
  [ 4005.426818] IP: [<c109a130>] page_cache_sync_readahead+0x18/0x3e

Signed-off-by: Wu Fengguang <24f7fe9d205c8a9f6ade0c2894e14303ca16087f@intel.com>
Cc: Yan Zheng <91a8aef18b3034feaa8db34be52d16294fee07db@21cn.com>
Reported-by: Kirill A. Shutemov <9b153e80bc985b32d577460a8a24e398d4182978@shutemov.name>
Tested-by: Kirill A. Shutemov <9b153e80bc985b32d577460a8a24e398d4182978@shutemov.name>
Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@kernel.org>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs