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    Subject[PATCH 5.13 378/800] block: fix trace completion for chained bio
    Date
    From: Edward Hsieh <edwardh@synology.com>

    [ Upstream commit 60b6a7e6a0f4382cd689f9afdac816964fec2921 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    block/bio.c | 13 ++++++-------
    1 file changed, 6 insertions(+), 7 deletions(-)

    diff --git a/block/bio.c b/block/bio.c
    index 44205dfb6b60..1fab762e079b 100644
    --- 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);
    --
    2.30.2


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