tracing: prevent NULL pointer dereference in ftrace_raw_event_block_bio_bounce

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@osadl.org>
LKML-Reference: <4AAAC9B1.9060505@osadl.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 9a74b468a229..d86af94691c2 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -171,6 +171,7 @@ TRACE_EVENT(block_rq_complete,
                   (unsigned long long)__entry->sector,
                   __entry->nr_sector, __entry->errors)
 );
+
 TRACE_EVENT(block_bio_bounce,
 
         TP_PROTO(struct request_queue *q, struct bio *bio),
@@ -186,7 +187,8 @@ TRACE_EVENT(block_bio_bounce,
         ),
 
         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);