block: fix trace completion for chained bio

For chained bio, trace_block_bio_complete in bio_endio is currently called
only by the parent bio once upon all chained bio completed.
However, the sector and size for the parent bio are modified in bio_split.
Therefore, the size and sector of the complete events might not match the
queue events in blktrace.

The original fix of bio completion trace <fbbaf700e7b1> ("block: trace
completion of all bios.") wants multiple complete events to correspond
to one queue event but missed this.

The issue can be reproduced by md/raid5 read with bio cross chunks.

To fix, move trace completion into the loop for every chained bio to call.

Fixes: fbbaf700e7b1 ("block: trace completion of all bios.")
Reviewed-by: Wade Liang <wadel@synology.com>
Reviewed-by: BingJing Chang <bingjingc@synology.com>
Signed-off-by: Edward Hsieh <edwardh@synology.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210624123030.27014-1-edwardh@synology.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index 44205df..1fab762 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -1375,8 +1375,7 @@ static inline bool bio_remaining_done(struct bio *bio)
  *
  *   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 called the
- *   last time.  At this point the BLK_TA_COMPLETE tracing event will be
- *   generated if BIO_TRACE_COMPLETION is set.
+ *   last time.
  **/
 void bio_endio(struct bio *bio)
 {
@@ -1389,6 +1388,11 @@ again:
        if (bio->bi_bdev)
                rq_qos_done_bio(bio->bi_bdev->bd_disk->queue, bio);
 
+       if (bio->bi_bdev && bio_flagged(bio, BIO_TRACE_COMPLETION)) {
+               trace_block_bio_complete(bio->bi_bdev->bd_disk->queue, bio);
+               bio_clear_flag(bio, BIO_TRACE_COMPLETION);
+       }
+
        /*
         * Need to have a real endio function for chained bios, otherwise
         * various corner cases will break (like stacking block devices that
@@ -1402,11 +1406,6 @@ again:
                goto again;
        }
 
-       if (bio->bi_bdev && bio_flagged(bio, BIO_TRACE_COMPLETION)) {
-               trace_block_bio_complete(bio->bi_bdev->bd_disk->queue, bio);
-               bio_clear_flag(bio, BIO_TRACE_COMPLETION);
-       }
-
        blk_throtl_bio_endio(bio);
        /* release cgroup info */
        bio_uninit(bio);