[PATCH] Prevent NULL pointer dereference in ftrace_raw_event_block_bio_bounce

[Carsten Emde]

Booting 2.6.31 and executing
  echo 1 >/sys/kernel/debug/tracing/events/enable
leads to
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<c032a583>] ftrace_raw_event_block_bio_bounce+0x4b/0xb9

Apparently,
  bio = bio_map_user(q, NULL, uaddr, len, reading, gfp_mask);
is called in block/blk-map.c:58 where bio->bi_bdev in set to NULL and 
still is NULL when an attempt is made to evaluate bio->bi_bdev->bd_dev 
in include/trace/events/block.h:189.

The tracepoint should ensure bio->bi_bdev is not dereferenced, if NULL.

Signed-Off-By: Carsten Emde <C.Emde@xxxxxxxxx>

--- a/include/trace/events/block.h 2009-09-11 21:20:56.000000000 +0200
+++ b/include/trace/events/block.h 2009-09-11 22:01:52.000000000 +0200
@@ -186,7 +186,8 @@
 	),

 	TP_fast_assign(
-		__entry->dev		= bio->bi_bdev->bd_dev;
+		__entry->dev		= bio->bi_bdev ?
+					  bio->bi_bdev->bd_dev : 0;
 		__entry->sector		= bio->bi_sector;
 		__entry->nr_sector	= bio->bi_size >> 9;
 		blk_fill_rwbs(__entry->rwbs, bio->bi_rw, bio->bi_size);

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