Re: [PATCH] md/raid1: fix writebehind bio clone

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On Wed, Jul 19, 2017 at 1:21 AM, Shaohua Li <shli@xxxxxxxxxx> wrote:
> From: Shaohua Li <shli@xxxxxx>
>
> After bio is submitted, we should not clone it as its bi_iter might be
> invalid by driver. This is the case of behind_master_bio. In certain
> situration, we could dispatch behind_master_bio immediately for the
> first disk and then clone it for other disks.

If I understand it correctly, it should be caused by dispatching
the master bio during the loop either via flushing plug or md_wakeup_thread().

If so, could we just add the bios into one temp pending list inside
the loop? Then
merge the temp list into conf->pending_bio_list after loop and
schedule to dispatch
them all? This way looks a bit more efficient.

Thanks,
Ming

>
> https://bugzilla.kernel.org/show_bug.cgi?id=196383
>
> Reported-by: Markus <m4rkusxxl@xxxxxx>
> Cc: Ming Lei <tom.leiming@xxxxxxxxx>
> Fix: 841c1316c7da(md: raid1: improve write behind)
> Cc: stable@xxxxxxxxxxxxxxx (4.12+)
> Signed-off-by: Shaohua Li <shli@xxxxxx>
> ---
>  drivers/md/raid1.c | 30 ++++++++++--------------------
>  1 file changed, 10 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 8387eb1540cd..5622f521830b 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -484,10 +484,6 @@ static void raid1_end_write_request(struct bio *bio)
>         }
>
>         if (behind) {
> -               /* we release behind master bio when all write are done */
> -               if (r1_bio->behind_master_bio == bio)
> -                       to_put = NULL;
> -
>                 if (test_bit(WriteMostly, &rdev->flags))
>                         atomic_dec(&r1_bio->behind_remaining);
>
> @@ -1080,7 +1076,7 @@ static void unfreeze_array(struct r1conf *conf)
>         wake_up(&conf->wait_barrier);
>  }
>
> -static struct bio *alloc_behind_master_bio(struct r1bio *r1_bio,
> +static void alloc_behind_master_bio(struct r1bio *r1_bio,
>                                            struct bio *bio)
>  {
>         int size = bio->bi_iter.bi_size;
> @@ -1090,7 +1086,7 @@ static struct bio *alloc_behind_master_bio(struct r1bio *r1_bio,
>
>         behind_bio = bio_alloc_mddev(GFP_NOIO, vcnt, r1_bio->mddev);
>         if (!behind_bio)
> -               goto fail;
> +               return;
>
>         /* discard op, we don't support writezero/writesame yet */
>         if (!bio_has_data(bio))
> @@ -1115,14 +1111,13 @@ static struct bio *alloc_behind_master_bio(struct r1bio *r1_bio,
>         r1_bio->behind_master_bio = behind_bio;;
>         set_bit(R1BIO_BehindIO, &r1_bio->state);
>
> -       return behind_bio;
> +       return;
>
>  free_pages:
>         pr_debug("%dB behind alloc failed, doing sync I/O\n",
>                  bio->bi_iter.bi_size);
>         bio_free_pages(behind_bio);
> -fail:
> -       return behind_bio;
> +       bio_put(behind_bio);
>  }
>
>  struct raid1_plug_cb {
> @@ -1475,7 +1470,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>                             (atomic_read(&bitmap->behind_writes)
>                              < mddev->bitmap_info.max_write_behind) &&
>                             !waitqueue_active(&bitmap->behind_wait)) {
> -                               mbio = alloc_behind_master_bio(r1_bio, bio);
> +                               alloc_behind_master_bio(r1_bio, bio);
>                         }
>
>                         bitmap_startwrite(bitmap, r1_bio->sector,
> @@ -1485,14 +1480,11 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>                         first_clone = 0;
>                 }
>
> -               if (!mbio) {
> -                       if (r1_bio->behind_master_bio)
> -                               mbio = bio_clone_fast(r1_bio->behind_master_bio,
> -                                                     GFP_NOIO,
> -                                                     mddev->bio_set);
> -                       else
> -                               mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
> -               }
> +               if (r1_bio->behind_master_bio)
> +                       mbio = bio_clone_fast(r1_bio->behind_master_bio,
> +                                             GFP_NOIO, mddev->bio_set);
> +               else
> +                       mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
>
>                 if (r1_bio->behind_master_bio) {
>                         if (test_bit(WriteMostly, &conf->mirrors[i].rdev->flags))
> @@ -2346,8 +2338,6 @@ static int narrow_write_error(struct r1bio *r1_bio, int i)
>                         wbio = bio_clone_fast(r1_bio->behind_master_bio,
>                                               GFP_NOIO,
>                                               mddev->bio_set);
> -                       /* We really need a _all clone */
> -                       wbio->bi_iter = (struct bvec_iter){ 0 };
>                 } else {
>                         wbio = bio_clone_fast(r1_bio->master_bio, GFP_NOIO,
>                                               mddev->bio_set);
> --
> 2.11.0
>



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