Currently only dm and md/raid5 bios trigger trace_block_bio_complete().
Now that we have bio_chain(), it is not possible, in general, for a
driver to know when the bio is really complete.  Only bio_endio()
knows that.

So move the trace_block_bio_complete() call to bio_endio().

Now trace_block_bio_complete() pairs with trace_block_bio_queue().
Any bio for which a 'queue' event is traced, will subsequently
generate a 'complete' event.

There are a few cases where completion tracing is not wanted.
1/ If blk_update_request() has already generated a completion
   trace event at the 'request' level, there is no point generating
   one at the bio level too.  In this case the bi_sector and bi_size
   will have changed, so the bio level event would be wrong

2/ If the bio hasn't actually been queued yet, but is being aborted
   early, then a trace event could be confusing.  Some filesystems
   call bio_endio() and will need to use a different interface to
   avoid tracing

3/ The bio_integrity code interposes itself by replacing bi_end_io,
   then restores it and calls bio_endio() again.  This would produce
   two identical trace events if left like that.

To handle these, we provide bio_endio_notrace().  This patch only adds
uses of this in core code.  Separate patches will be needed to update
the filesystems to avoid tracing.

Signed-off-by: NeilBrown <ne...@suse.com>
---
 block/bio-integrity.c |  4 ++--
 block/bio.c           | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk-core.c      |  2 +-
 drivers/md/dm.c       |  1 -
 drivers/md/raid5.c    |  8 --------
 include/linux/bio.h   |  1 +
 6 files changed, 50 insertions(+), 12 deletions(-)

diff --git a/block/bio-integrity.c b/block/bio-integrity.c
index 5384713d48bc..28581e2f68fb 100644
--- a/block/bio-integrity.c
+++ b/block/bio-integrity.c
@@ -370,7 +370,7 @@ static void bio_integrity_verify_fn(struct work_struct 
*work)
 
        /* Restore original bio completion handler */
        bio->bi_end_io = bip->bip_end_io;
-       bio_endio(bio);
+       bio_endio_notrace(bio);
 }
 
 /**
@@ -397,7 +397,7 @@ void bio_integrity_endio(struct bio *bio)
         */
        if (bio->bi_error) {
                bio->bi_end_io = bip->bip_end_io;
-               bio_endio(bio);
+               bio_endio_notrace(bio);
 
                return;
        }
diff --git a/block/bio.c b/block/bio.c
index 5eec5e08417f..c8e5d24abd52 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1811,6 +1811,45 @@ static inline bool bio_remaining_done(struct bio *bio)
 }
 
 /**
+ * bio_endio_notrace - end I/O on a bio without tracing
+ * @bio:       bio
+ *
+ * Description:
+ *   bio_endio_notrace() will end I/O on the whole bio.
+ *   bio_endio_notrace() should only be call if a completion trace
+ *   event is not needed.  This can be the case if a request-level
+ *   completion event has already been generated, if the bio is
+ *   being completed early, before it was even queued.
+ *
+ **/
+void bio_endio_notrace(struct bio *bio)
+{
+again:
+       if (!bio_remaining_done(bio))
+               return;
+
+       /*
+        * Need to have a real endio function for chained bios, otherwise
+        * various corner cases will break (like stacking block devices that
+        * save/restore bi_end_io) - however, we want to avoid unbounded
+        * recursion and blowing the stack. Tail call optimization would
+        * handle this, but compiling with frame pointers also disables
+        * gcc's sibling call optimization.
+        */
+       if (bio->bi_end_io == bio_chain_endio) {
+               bio = __bio_chain_endio(bio);
+               goto again;
+       }
+
+       if (bio->bi_bdev)
+               trace_block_bio_complete(bdev_get_queue(bio->bi_bdev),
+                                        bio, bio->bi_error);
+       if (bio->bi_end_io)
+               bio->bi_end_io(bio);
+}
+EXPORT_SYMBOL(bio_endio_notrace);
+
+/**
  * bio_endio - end I/O on a bio
  * @bio:       bio
  *
@@ -1818,6 +1857,10 @@ static inline bool bio_remaining_done(struct bio *bio)
  *   bio_endio() will end I/O on the whole bio. bio_endio() is the preferred
  *   way to end I/O on a bio. No one should call bi_end_io() directly on a
  *   bio unless they own it and thus know that it has an end_io function.
+ *
+ *   bio_endio() can be called several times on a bio that has been chained
+ *   using bio_chain().  The ->bi_end_io() function will only be call the
+ *   time.  At this point the BLK_TA_COMPLETE tracing event will be generated.
  **/
 void bio_endio(struct bio *bio)
 {
@@ -1838,6 +1881,9 @@ void bio_endio(struct bio *bio)
                goto again;
        }
 
+       if (bio->bi_bdev)
+               trace_block_bio_complete(bdev_get_queue(bio->bi_bdev),
+                                        bio, bio->bi_error);
        if (bio->bi_end_io)
                bio->bi_end_io(bio);
 }
diff --git a/block/blk-core.c b/block/blk-core.c
index 0eeb99ef654f..b6c76580a796 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -142,7 +142,7 @@ static void req_bio_endio(struct request *rq, struct bio 
*bio,
 
        /* don't actually finish bio if it's part of flush sequence */
        if (bio->bi_iter.bi_size == 0 && !(rq->rq_flags & RQF_FLUSH_SEQ))
-               bio_endio(bio);
+               bio_endio_notrace(bio);
 }
 
 void blk_dump_rq_flags(struct request *rq, char *msg)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f4ffd1eb8f44..f5f09ace690a 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -810,7 +810,6 @@ 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->bi_error = io_error;
                        bio_endio(bio);
                }
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 9a3b7da34137..f684cb566721 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5141,8 +5141,6 @@ static void raid5_align_endio(struct bio *bi)
        rdev_dec_pending(rdev, conf->mddev);
 
        if (!error) {
-               trace_block_bio_complete(bdev_get_queue(raid_bi->bi_bdev),
-                                        raid_bi, 0);
                bio_endio(raid_bi);
                if (atomic_dec_and_test(&conf->active_aligned_reads))
                        wake_up(&conf->wait_for_quiescent);
@@ -5727,10 +5725,6 @@ static void raid5_make_request(struct mddev *mddev, 
struct bio * bi)
                md_write_end(mddev);
        remaining = raid5_dec_bi_active_stripes(bi);
        if (remaining == 0) {
-
-
-               trace_block_bio_complete(bdev_get_queue(bi->bi_bdev),
-                                        bi, 0);
                bio_endio(bi);
        }
 }
@@ -6138,8 +6132,6 @@ static int  retry_aligned_read(struct r5conf *conf, 
struct bio *raid_bio)
        }
        remaining = raid5_dec_bi_active_stripes(raid_bio);
        if (remaining == 0) {
-               trace_block_bio_complete(bdev_get_queue(raid_bio->bi_bdev),
-                                        raid_bio, 0);
                bio_endio(raid_bio);
        }
        if (atomic_dec_and_test(&conf->active_aligned_reads))
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8e521194f6fc..e0552bee227b 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -418,6 +418,7 @@ static inline struct bio *bio_clone_kmalloc(struct bio 
*bio, gfp_t gfp_mask)
 extern blk_qc_t submit_bio(struct bio *);
 
 extern void bio_endio(struct bio *);
+extern void bio_endio_notrace(struct bio *);
 
 static inline void bio_io_error(struct bio *bio)
 {
-- 
2.12.0

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