linux-kernel - Re: [PATCH v2 1/2] md: factor out a new helper to put mddev

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Date:   Wed, 27 Sep 2023 08:54:54 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Song Liu <song@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     mariusz.tkaczyk@...ux.intel.com, xni@...hat.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 v2 1/2] md: factor out a new helper to put mddev

Hi,

在 2023/09/27 8:15, Song Liu 写道:
> On Mon, Sep 25, 2023 at 8:04 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> There are no functional changes, the new helper will still hold
>> 'all_mddevs_lock' after putting mddev, and it will be used to simplify
>> md_seq_ops.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>>   drivers/md/md.c | 18 +++++++++++++++---
>>   1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index 10cb4dfbf4ae..a5ef6f7da8ec 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -616,10 +616,15 @@ static inline struct mddev *mddev_get(struct mddev *mddev)
>>
>>   static void mddev_delayed_delete(struct work_struct *ws);
>>
>> -void mddev_put(struct mddev *mddev)
>> +static void __mddev_put(struct mddev *mddev, bool locked)
>>   {
>> -       if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
>> +       if (locked) {
>> +               spin_lock(&all_mddevs_lock);
>> +               if (!atomic_dec_and_test(&mddev->active))
>> +                       return;
>> +       } else if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
>>                  return;
>> +
> 
> This condition is indeed very confusing. No matter whether we call the
> flag "locked" or "do_lock", it is not really accurate.
> 
> How about we factor out a helper with the following logic:
> 
>          if (!mddev->raid_disks && list_empty(&mddev->disks) &&
>              mddev->ctime == 0 && !mddev->hold_active) {
>                  /* Array is not configured at all, and not held active,
>                   * so destroy it */
>                  set_bit(MD_DELETED, &mddev->flags);
> 
>                  /*
>                   * Call queue_work inside the spinlock so that
>                   * flush_workqueue() after mddev_find will succeed in waiting
>                   * for the work to be done.
>                   */
>                  queue_work(md_misc_wq, &mddev->del_work);
>          }
> 
> and then use it at the two callers?
> 
> Does this make sense?

Yes, that sounds great. I'll do this in v3.

Thanks,
Kuai

> 
> Thanks,
> Song
> .
>