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From:   Jack Wang <jack.wang.usish@gmail.com>
Date:   Wed, 26 Jan 2022 11:09:46 +0100
Message-ID: <CA+res+S1GcDzM6hnmar+s1k3ggswURZ+_8BqweifShCTjVJ2aQ@mail.gmail.com>
Subject: Re: [PATCH 5.10 01/25] md: revert io stats accounting
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable <stable@vger.kernel.org>,
        Guoqing Jiang <jiangguoqing@kylinos.cn>,
        Song Liu <song@kernel.org>,
        Guillaume Morin <guillaume@morinfr.org>
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Hi,

Greg Kroah-Hartman <gregkh@linuxfoundation.org> =E4=BA=8E2022=E5=B9=B41=E6=
=9C=8814=E6=97=A5=E5=91=A8=E4=BA=94 19:57=E5=86=99=E9=81=93=EF=BC=9A
>
> From: Guoqing Jiang <jgq516@gmail.com>
>
> commit ad3fc798800fb7ca04c1dfc439dba946818048d8 upstream.
>
> The commit 41d2d848e5c0 ("md: improve io stats accounting") could cause
> double fault problem per the report [1], and also it is not correct to
> change ->bi_end_io if md don't own it, so let's revert it.
>
> And io stats accounting will be replemented in later commits.
>
> [1]. https://lore.kernel.org/linux-raid/3bf04253-3fad-434a-63a7-20214e38c=
f26@gmail.com/T/#t
>
> Fixes: 41d2d848e5c0 ("md: improve io stats accounting")
> Signed-off-by: Guoqing Jiang <jiangguoqing@kylinos.cn>
> Signed-off-by: Song Liu <song@kernel.org>
> [GM: backport to 5.10-stable]
> Signed-off-by: Guillaume Morin <guillaume@morinfr.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/md/md.c |   57 +++++++++++--------------------------------------=
-------
>  drivers/md/md.h |    1
>  2 files changed, 12 insertions(+), 46 deletions(-)
>
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -459,34 +459,12 @@ check_suspended:
>  }
>  EXPORT_SYMBOL(md_handle_request);
>
> -struct md_io {
> -       struct mddev *mddev;
> -       bio_end_io_t *orig_bi_end_io;
> -       void *orig_bi_private;
> -       unsigned long start_time;
> -       struct hd_struct *part;
> -};
> -
> -static void md_end_io(struct bio *bio)
> -{
> -       struct md_io *md_io =3D bio->bi_private;
> -       struct mddev *mddev =3D md_io->mddev;
> -
> -       part_end_io_acct(md_io->part, bio, md_io->start_time);
> -
> -       bio->bi_end_io =3D md_io->orig_bi_end_io;
> -       bio->bi_private =3D md_io->orig_bi_private;
> -
> -       mempool_free(md_io, &mddev->md_io_pool);
> -
> -       if (bio->bi_end_io)
> -               bio->bi_end_io(bio);
> -}
> -
>  static blk_qc_t md_submit_bio(struct bio *bio)
>  {
>         const int rw =3D bio_data_dir(bio);
> +       const int sgrp =3D op_stat_group(bio_op(bio));
>         struct mddev *mddev =3D bio->bi_disk->private_data;
> +       unsigned int sectors;
>
>         if (mddev =3D=3D NULL || mddev->pers =3D=3D NULL) {
>                 bio_io_error(bio);
> @@ -507,26 +485,21 @@ static blk_qc_t md_submit_bio(struct bio
>                 return BLK_QC_T_NONE;
>         }
>
> -       if (bio->bi_end_io !=3D md_end_io) {
> -               struct md_io *md_io;
> -
> -               md_io =3D mempool_alloc(&mddev->md_io_pool, GFP_NOIO);
> -               md_io->mddev =3D mddev;
> -               md_io->orig_bi_end_io =3D bio->bi_end_io;
> -               md_io->orig_bi_private =3D bio->bi_private;
> -
> -               bio->bi_end_io =3D md_end_io;
> -               bio->bi_private =3D md_io;
> -
> -               md_io->start_time =3D part_start_io_acct(mddev->gendisk,
> -                                                      &md_io->part, bio)=
;
> -       }
> -
> +       /*
> +        * save the sectors now since our bio can
> +        * go away inside make_request
> +        */
> +       sectors =3D bio_sectors(bio);
This code snip is not inside the original patch, and it's not in
latest upstream too.
>         /* bio could be mergeable after passing to underlayer */
>         bio->bi_opf &=3D ~REQ_NOMERGE;
>
>         md_handle_request(mddev, bio);
>
> +       part_stat_lock();
> +       part_stat_inc(&mddev->gendisk->part0, ios[sgrp]);
> +       part_stat_add(&mddev->gendisk->part0, sectors[sgrp], sectors);
> +       part_stat_unlock();
> +
same here, this code snip is not inside the original patch, and it's
not in latest upstream too.

I think would be good keep it as the upstream version.

Best!
Jinpu Wang @ IONOS
>         return BLK_QC_T_NONE;
>  }
>
> @@ -5636,7 +5609,6 @@ static void md_free(struct kobject *ko)
>
>         bioset_exit(&mddev->bio_set);
>         bioset_exit(&mddev->sync_set);
> -       mempool_exit(&mddev->md_io_pool);
>         kfree(mddev);
>  }
>
> @@ -5732,11 +5704,6 @@ static int md_alloc(dev_t dev, char *nam
>                  */
>                 mddev->hold_active =3D UNTIL_STOP;
>
> -       error =3D mempool_init_kmalloc_pool(&mddev->md_io_pool, BIO_POOL_=
SIZE,
> -                                         sizeof(struct md_io));
> -       if (error)
> -               goto abort;
> -
>         error =3D -ENOMEM;
>         mddev->queue =3D blk_alloc_queue(NUMA_NO_NODE);
>         if (!mddev->queue)
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -487,7 +487,6 @@ struct mddev {
>         struct bio_set                  sync_set; /* for sync operations =
like
>                                                    * metadata and bitmap =
writes
>                                                    */
> -       mempool_t                       md_io_pool;
>
>         /* Generic flush handling.
>          * The last to finish preflush schedules a worker to submit
>
>