linux-kernel - Re: [PATCH -next v3 4/7] md: factor out a helper rdev_removeable() from remove_and_add

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Message-ID: <CALTww29j+xQ2y+0eSutuNUDEVfoPaHmS3BDPNdg+wxDNOrHGKw@mail.gmail.com>
Date:   Wed, 23 Aug 2023 11:42:41 +0800
From:   Xiao Ni <xni@...hat.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     song@...nel.org, mariusz.tkaczyk@...ux.intel.com,
        linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next v3 4/7] md: factor out a helper rdev_removeable()
 from remove_and_add_spares()

On Wed, Aug 23, 2023 at 10:45 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2023/08/22 18:19, Xiao Ni 写道:
> > On Sun, Aug 20, 2023 at 5:13 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
> >>
> >> From: Yu Kuai <yukuai3@...wei.com>
> >>
> >> There are no functional changes, just to make the code simpler and
> >> prepare to delay remove_and_add_spares() to md_start_sync().
> >>
> >> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> >> ---
> >>   drivers/md/md.c | 33 +++++++++++++++++++--------------
> >>   1 file changed, 19 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/drivers/md/md.c b/drivers/md/md.c
> >> index 561cac13ff96..ceace5ffadd6 100644
> >> --- a/drivers/md/md.c
> >> +++ b/drivers/md/md.c
> >> @@ -9153,6 +9153,22 @@ void md_do_sync(struct md_thread *thread)
> >>   }
> >>   EXPORT_SYMBOL_GPL(md_do_sync);
> >>
> >> +static bool rdev_removeable(struct md_rdev *rdev)
> >> +{
> >> +       if (rdev->raid_disk < 0 || test_bit(Blocked, &rdev->flags) ||
> >> +           atomic_read(&rdev->nr_pending))
> >> +               return false;
> >> +
> >> +       if (test_bit(RemoveSynchronized, &rdev->flags))
> >> +               return true;
> >> +
> >> +       if (test_bit(In_sync, &rdev->flags) ||
> >> +           test_bit(Journal, &rdev->flags))
> >> +               return false;
> >> +
> >> +       return true;
> >> +}
> >> +
> >>   static int remove_and_add_spares(struct mddev *mddev,
> >>                                   struct md_rdev *this)
> >>   {
> >> @@ -9166,11 +9182,7 @@ static int remove_and_add_spares(struct mddev *mddev,
> >>                  return 0;
> >>
> >>          rdev_for_each(rdev, mddev) {
> >> -               if ((this == NULL || rdev == this) &&
> >> -                   rdev->raid_disk >= 0 &&
> >> -                   !test_bit(Blocked, &rdev->flags) &&
> >> -                   test_bit(Faulty, &rdev->flags) &&
> >> -                   atomic_read(&rdev->nr_pending)==0) {
> >> +               if ((this == NULL || rdev == this) && rdev_removeable(rdev)) {
> >
> > There is a small change with the original method. Before this patch,
> > it checks the Faulty flag when setting RemoveSynchronized and it
> > checks RemoveSynchronized and "!In_sync && !Journal". I'm not sure if
> > it's right or not.
>
> Yes, there is a small change. After a second thought, I think it's OK
> to leave the code to set RemoveSynchronized where it is for now, because
> it'll be removed later. I don't need to bother factor out a common code
> to set RemoveSynchronized and call hot_remove_disk().

This will be easier for review, thanks.

>
> By the way, once refactor of mddev_suspend() is done, then access to
> rdev from fastpath will be replaced from:
>
> rcu_read_lock()
> ...
> rcu_read_unlock()
>
> to:
>
> md_array_enter()
> // grab 'active_io', 'active_io' will probably be renamed
> ...
> md_array_exit()
>
> That's why I said RemoveSynchronized will be removed.

:) I'll try to understand it in your following patches.

Regards
Xiao
>
> Thanks,
> Kuai
>
> >
> >>                          /* Faulty non-Blocked devices with nr_pending == 0
> >>                           * never get nr_pending incremented,
> >>                           * never get Faulty cleared, and never get Blocked set.
> >> @@ -9185,19 +9197,12 @@ static int remove_and_add_spares(struct mddev *mddev,
> >>                  synchronize_rcu();
> >>          rdev_for_each(rdev, mddev) {
> >>                  if ((this == NULL || rdev == this) &&
> >> -                   rdev->raid_disk >= 0 &&
> >> -                   !test_bit(Blocked, &rdev->flags) &&
> >> -                   ((test_bit(RemoveSynchronized, &rdev->flags) ||
> >> -                    (!test_bit(In_sync, &rdev->flags) &&
> >> -                     !test_bit(Journal, &rdev->flags))) &&
> >> -                   atomic_read(&rdev->nr_pending)==0)) {
> >> -                       if (mddev->pers->hot_remove_disk(
> >> -                                   mddev, rdev) == 0) {
> >> +                   rdev_removeable(rdev) &&
> >> +                   mddev->pers->hot_remove_disk(mddev, rdev) == 0) {
> >>                                  sysfs_unlink_rdev(mddev, rdev);
> >>                                  rdev->saved_raid_disk = rdev->raid_disk;
> >>                                  rdev->raid_disk = -1;
> >>                                  removed++;
> >> -                       }
> >>                  }
> >>                  if (remove_some && test_bit(RemoveSynchronized, &rdev->flags))
> >>                          clear_bit(RemoveSynchronized, &rdev->flags);
> >> --
> >> 2.39.2
> >>
> >
> > .
> >
>