block: add missing block_bio_complete() tracepoint

bio completion didn't kick block_bio_complete TP.  Only dm was
explicitly triggering the TP on IO completion.  This makes
block_bio_complete TP useless for tracers which want to know about
bios, and all other bio based drivers skip generating blktrace
completion events.

This patch makes all bio completions via bio_endio() generate
block_bio_complete TP.

* Explicit trace_block_bio_complete() invocation removed from dm and
  the trace point is unexported.

* @rq dropped from trace_block_bio_complete().  bios may fly around
  w/o queue associated.  Verifying and accessing the assocaited queue
  belongs to TP probes.

* blktrace now gets both request and bio completions.  Make it ignore
  bio completions if request completion path is happening.

This makes all bio based drivers generate blktrace completion events
properly and makes the block_bio_complete TP actually useful.

v2: With this change, block_bio_complete TP could be invoked on sg
    commands which have bio's with %NULL bi_bdev.  Update TP
    assignment code to check whether bio->bi_bdev is %NULL before
    dereferencing.

Signed-off-by: Tejun Heo <tj@kernel.org>
Original-patch-by: Namhyung Kim <namhyung@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 23 insertions, 3 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index c0bd030..190d98f 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -739,6 +739,12 @@ static void blk_add_trace_rq_complete(void *ignore,
 				      struct request_queue *q,
 				      struct request *rq)
 {
+	struct blk_trace *bt = q->blk_trace;
+
+	/* if control ever passes through here, it's a request based driver */
+	if (unlikely(bt && !bt->rq_based))
+		bt->rq_based = true;
+
 	blk_add_trace_rq(q, rq, BLK_TA_COMPLETE);
 }
 
@@ -774,10 +780,24 @@ static void blk_add_trace_bio_bounce(void *ignore,
 	blk_add_trace_bio(q, bio, BLK_TA_BOUNCE, 0);
 }
 
-static void blk_add_trace_bio_complete(void *ignore,
-				       struct request_queue *q, struct bio *bio,
-				       int error)
+static void blk_add_trace_bio_complete(void *ignore, struct bio *bio, int error)
 {
+	struct request_queue *q;
+	struct blk_trace *bt;
+
+	if (!bio->bi_bdev)
+		return;
+
+	q = bdev_get_queue(bio->bi_bdev);
+	bt = q->blk_trace;
+
+	/*
+	 * Request based drivers will generate both rq and bio completions.
+	 * Ignore bio ones.
+	 */
+	if (likely(!bt) || bt->rq_based)
+		return;
+
 	blk_add_trace_bio(q, bio, BLK_TA_COMPLETE, error);
 }