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 <[email protected]>
Cc: Yan Zheng <[email protected]>
Reported-by: Kirill A. Shutemov <[email protected]>
Tested-by: Kirill A. Shutemov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/readahead.c b/mm/readahead.c
index 999b54bb462f3ad24ec83b8997aec7c7780bc469..dfa9a1a03a116c7659d0d71134a3450a8d69026f 100644 (file)
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -503,7 +503,7 @@ void page_cache_sync_readahead(struct address_space *mapping,
                return;
 
        /* be dumb */
-       if (filp->f_mode & FMODE_RANDOM) {
+       if (filp && (filp->f_mode & FMODE_RANDOM)) {
                force_page_cache_readahead(mapping, filp, offset, req_size);
                return;
        }