linux-kernel - Re: [PATCH 08/12] dm: dm.c: replace 'bio->bi_vcnt == 1' with !bio_multiple

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Date:   Tue, 15 Nov 2016 09:03:14 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Jens Axboe <axboe@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     linux-block <linux-block@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ming Lei <tom.leiming@...il.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        "maintainer:DEVICE-MAPPER (LVM)" <dm-devel@...hat.com>,
        Shaohua Li <shli@...nel.org>,
        "open list:SOFTWARE RAID (Multiple Disks) SUPPORT" 
        <linux-raid@...r.kernel.org>
Subject: Re: [PATCH 08/12] dm: dm.c: replace 'bio->bi_vcnt == 1' with !bio_multiple_segments

On Fri, Nov 11, 2016 at 8:05 PM, Ming Lei <tom.leiming@...il.com> wrote:
> Avoid to access .bi_vcnt directly, because the bio can be
> splitted from block layer, and .bi_vcnt should never have
> been used here.
>
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
>  drivers/md/dm-rq.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
> index b2a9e2d161e4..d9cc8324e597 100644
> --- a/drivers/md/dm-rq.c
> +++ b/drivers/md/dm-rq.c
> @@ -797,8 +797,13 @@ static void dm_old_request_fn(struct request_queue *q)
>                 if (req_op(rq) != REQ_OP_FLUSH)
>                         pos = blk_rq_pos(rq);
>
> +               /*
> +                * bio can be splitted from block layer, so use
> +                * !bio_multiple_segments instead of 'bio->bi_vcnt == 1'
> +                */
>                 if ((dm_old_request_peeked_before_merge_deadline(md) &&
> -                    md_in_flight(md) && rq->bio && rq->bio->bi_vcnt == 1 &&
> +                    md_in_flight(md) && rq->bio &&
> +                    !bio_multiple_segments(rq->bio) &&
>                      md->last_rq_pos == pos && md->last_rq_rw == rq_data_dir(rq)) ||
>                     (ti->type->busy && ti->type->busy(ti))) {
>                         blk_delay_queue(q, 10);

Hi Alasdair, Mike, Christoph and anyone,

Could you give this one a review?

Thanks,
Ming Lei