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

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Message-ID: <20230926144536.0000017d@linux.intel.com>
Date:   Tue, 26 Sep 2023 14:45:36 +0200
From:   Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     xni@...hat.com, song@...nel.org, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com,
        yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v2 1/2] md: factor out a new helper to put mddev

On Tue, 26 Sep 2023 10:58:26 +0800
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;

It is "locked" and we are taking lock? It seems weird to me. Perhaps "do_lock"
would be better? Do you meant "lockdep_assert_held(&all_mddevs_lock);"

Something is wrong here, we have two paths and in both cases we are
taking lock.

> +	} else if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
>  		return;
> +
>  	if (!mddev->raid_disks && list_empty(&mddev->disks) &&
>  	    mddev->ctime == 0 && !mddev->hold_active) {
>  		/* Array is not configured at all, and not held active,
> @@ -633,7 +638,14 @@ void mddev_put(struct mddev *mddev)
>  		 */
>  		queue_work(md_misc_wq, &mddev->del_work);
>  	}
> -	spin_unlock(&all_mddevs_lock);
> +
> +	if (!locked)
> +		spin_unlock(&all_mddevs_lock);
As above, I'm not sure if it is correct.

Thanks,
Mariusz