Re: [PATCH -next v3 6/7] md: factor out a helper rdev_addable() from remove_and_add_spares()

[Song Liu]

On Tue, Aug 22, 2023 at 8:04 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> 在 2023/08/22 10:17, Yu Kuai 写道:
> > Hi,
> >
> > 在 2023/08/22 7:22, Song Liu 写道:
> >> On Sun, Aug 20, 2023 at 2:13 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> >>>
> >>> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >>>
> >>> 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@xxxxxxxxxx>
> >>> ---
> >>>   drivers/md/md.c | 28 ++++++++++++++++------------
> >>>   1 file changed, 16 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/drivers/md/md.c b/drivers/md/md.c
> >>> index 11d27c934fdd..cdc361c521d4 100644
> >>> --- a/drivers/md/md.c
> >>> +++ b/drivers/md/md.c
> >>> @@ -9177,6 +9177,20 @@ static bool rdev_is_spare(struct md_rdev *rdev)
> >>>                 !test_bit(Faulty, &rdev->flags);
> >>>   }
> >>>
> >>> +static bool rdev_addable(struct md_rdev *rdev)
> >>> +{
> >>> +       if (test_bit(Candidate, &rdev->flags) || rdev->raid_disk >= 0 ||
> >>> +           test_bit(Faulty, &rdev->flags))
> >>> +               return false;
> >>> +
> >>> +       if (!test_bit(Journal, &rdev->flags) &&
> >>> !md_is_rdwr(rdev->mddev) &&
> >>
> >> Instead of straightforward refactoring, I hope we can make these rdev_*
> >> helpers more meaningful, and hopefullly reusable. For example, let's
> >> define
> >> the meaning of "addable", and write the function to match that
> >> meaning. In
> >> this case, I think we shouldn't check md_is_rdwr() inside rdev_addable().
> >>
> >> Does this make sense?
> >
> > Yes, this make sense, rdev can be added to read-only array.
> >
> > There are total three callers of pers->hot_add_sisk, I'll try to find if
> > they have common conditions.
>
> Unfortunately, the conditions is quite different, and It's difficult to
> factor out a common helper for them to use.
>
> In this case, !md_is_rdwr() is one of the four conditions, which means
> if the array is read-only, there is a special case that rdev can't be
> added to the configuration. Perhaps it's okay to keep this?

My main concern is that rdev_addable() is not making the code easier to
understand. We have a few different cases at this point:

1. rdev is not suitable for add (Faulty, raid_disk>=0, Candidate);
2. rdev is Journal;
3. Re-add rdev to RO array;
4. Non-re-add rdev to RO array;
5. Other cases.

Current rdev_addable() handles more or less all of this, which is
confusing. Maybe we can do something along similar to the
following (not tested). Does this look more clear?

Thanks,
Song

diff --git i/drivers/md/md.c w/drivers/md/md.c
index 78be7811a89f..8cb855d03e0a 100644
--- i/drivers/md/md.c
+++ w/drivers/md/md.c
@@ -9117,6 +9117,20 @@ void md_do_sync(struct md_thread *thread)
 }
 EXPORT_SYMBOL_GPL(md_do_sync);

+static bool rdev_addable(struct md_rdev *rdev)
+{
+       if (test_bit(Candidate, &rdev->flags) || rdev->raid_disk >= 0 ||
+           test_bit(Faulty, &rdev->flags))
+               return false;
+       return true;
+}
+
+static bool rdev_is_readd(struct md_rdev *rdev)
+{
+       return rdev->saved_raid_disk >= 0 ||
+               !test_bit(Bitmap_sync, &rdev->flags);
+}
+
 static int remove_and_add_spares(struct mddev *mddev,
                                 struct md_rdev *this)
 {
@@ -9176,25 +9190,24 @@ static int remove_and_add_spares(struct mddev *mddev,
        rdev_for_each(rdev, mddev) {
                if (this && this != rdev)
                        continue;
-               if (test_bit(Candidate, &rdev->flags))
-                       continue;
                if (rdev->raid_disk >= 0 &&
                    !test_bit(In_sync, &rdev->flags) &&
                    !test_bit(Journal, &rdev->flags) &&
                    !test_bit(Faulty, &rdev->flags))
                        spares++;
-               if (rdev->raid_disk >= 0)
+
+               if (!rdev_addable(rdev))
                        continue;
-               if (test_bit(Faulty, &rdev->flags))
+
+               if (test_bit(Journal, &rdev->flags))
+                       goto hot_add_disk;
+
+               if (!md_is_rdwr(mddev) && !rdev_is_readd(rdev))
                        continue;
-               if (!test_bit(Journal, &rdev->flags)) {
-                       if (!md_is_rdwr(mddev) &&
-                           !(rdev->saved_raid_disk >= 0 &&
-                             !test_bit(Bitmap_sync, &rdev->flags)))
-                               continue;

-                       rdev->recovery_offset = 0;
-               }
+               rdev->recovery_offset = 0;
+
+       hot_add_disk:
                if (mddev->pers->hot_add_disk(mddev, rdev) == 0) {
                        /* failure here is OK */
                        sysfs_link_rdev(mddev, rdev);