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: <941be671-0d33-ef3a-8e81-d89af66b38a4@huaweicloud.com>
Date:   Wed, 23 Aug 2023 10:45:11 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Xiao Ni <xni@...hat.com>, 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()

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().

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.

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
>>
> 
> .
>