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

From: Yu Kuai
Date: Wed Aug 23 2023 - 04:43:06 EST

Hi,

在 2023/08/23 13:26, Song Liu 写道:
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);
This should use '&&' instead of '||' ?

+}
+
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;
+

I understand what you mean now, but I must use the exact same judgement
in the new helper md_spares_need_change() in patch 7, there will be redundant code this way.

How about this, rework rdev_addable():

static bool rdev_addable(struct md_rdev *rdev)
{
+ /* rdev is already used, don't add it again. */
if (test_bit(Candidate, &rdev->flags) || rdev->raid_disk >= 0 ||
test_bit(Faulty, &rdev->flags))
return false;

~ /* Allow to add journal disk. */
~ if (test_bit(Journal, &rdev->flags))
~_ return true;

~ /* Allow to add if array is read-write. */
+ if (md_is_rdwr(rdev->mddev))
+ return true;
+
+ /*
+ * For read-only array, only allow to readd a rdev. And if bitmap is
+ * used, don't allow to readd a rdev that is too old.
+ */
+ if (rdev->saved_raid_disk >=0 && !test_bit(Bitmap_sync, &rdev->flags))
+ return true;
+
+ return false;
}


Thanks,
Kuai

+ 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);
.