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Re: [dm-devel] [PATCH] block: add missing block_bio_complete() tracepoint



2012-01-29 6:41 PM, Namhyung Kim wrote:
The block_bio_complete() TP has been missed so long, so that bio-based
drivers haven't been able to trace its IO behavior. Add it.

In some rare cases, such as loop_switch, @bio->bi_bdev can be NULL.
Thus convert it to TRACE_EVENT_CONDITION() as Steven suggested.


Now I see that it seems TRACE_EVENT_CONDITION() can protect event tracing from such condition, but what about other users of the TP like blktrace? I think it'll still get NULL pointer dereference on bdev_get_queue() after the change, right? If so, convert to T_E_C() looks meaningless IMHO. Do I miss something?

Thanks,
Namhyung


 From now on, request-based drivers will also get BLK_TA_COMPLETEs for
all bio's in requests. This needs to be handled in userland properly.

Also remove external use of the TP in DM and unexport it.

Signed-off-by: Namhyung Kim <namhyung gmail com>
Cc: Tejun Heo <tj kernel org>
Cc: Steven Rostedt <rostedt goodmis org>
Cc: dm-devel redhat com
---
* v2:
  - Merge previous patches into one as suggested by Tejun.
  - Drop BIO_COMPLETE_MASK. Now I think it should be handled in userland
    like other (maybe duplicated, in some sense) bio complete reports.

  block/blk-core.c             |    1 -
  drivers/md/dm.c              |    1 -
  fs/bio.c                     |    2 ++
  include/trace/events/block.h |    4 +++-
  4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 1b4fd93af2c0..399c128f516c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -37,7 +37,6 @@

  EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
  EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
-EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);

  DEFINE_IDA(blk_queue_ida);

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4720f68f817e..01185fa0eb74 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -648,7 +648,6 @@ static void dec_pending(struct dm_io *io, int error)
  			queue_io(md, bio);
  		} else {
  			/* done with normal IO or empty flush */
-			trace_block_bio_complete(md->queue, bio, io_error);
  			bio_endio(bio, io_error);
  		}
  	}
diff --git a/fs/bio.c b/fs/bio.c
index b1fe82cf88cf..14c03eaf384e 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1447,6 +1447,8 @@ void bio_endio(struct bio *bio, int error)
  	else if (!test_bit(BIO_UPTODATE,&bio->bi_flags))
  		error = -EIO;

+	trace_block_bio_complete(bdev_get_queue(bio->bi_bdev), bio, error);
+
  	if (bio->bi_end_io)
  		bio->bi_end_io(bio, error);
  }
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 05c5e61f0a7c..96955f4828b3 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -213,12 +213,14 @@ TRACE_EVENT(block_bio_bounce,
   * This tracepoint indicates there is no further work to do on this
   * block IO operation @bio.
   */
-TRACE_EVENT(block_bio_complete,
+TRACE_EVENT_CONDITION(block_bio_complete,

  	TP_PROTO(struct request_queue *q, struct bio *bio, int error),

  	TP_ARGS(q, bio, error),

+	TP_CONDITION(bio->bi_bdev != NULL),
+
  	TP_STRUCT__entry(
  		__field( dev_t,		dev		)
  		__field( sector_t,	sector		)


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