[046/197] readahead: fix NULL filp dereference

[Greg KH]

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Wu Fengguang <fengguang.wu@xxxxxxxxx>

commit 70655c06bd3f25111312d63985888112aed15ac5 upstream.

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 <fengguang.wu@xxxxxxxxx>
Cc: Yan Zheng <yanzheng@xxxxxxxx>
Reported-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Tested-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/readahead.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -502,7 +502,7 @@ void page_cache_sync_readahead(struct ad
 		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;
 	}


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