linux-kernel - Re: [PATCH] md: get rdev->mddev with READ

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Date: Tue, 2 Jan 2024 14:16:32 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Li Lingfeng <lilingfeng@...weicloud.com>, song@...nel.org
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 linan122@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com,
 lilingfeng3@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] md: get rdev->mddev with READ_ONCE()

在 2023/12/29 15:05, Li Lingfeng 写道:
> From: Li Lingfeng <lilingfeng3@...wei.com>
> 
> Users may get rdev->mddev by sysfs while rdev is releasing.
> So use both READ_ONCE() and WRITE_ONCE() to prevent load/store tearing
> and to read/write mddev atomically.

LGTM
Reviewed-by: Yu Kuai <yukuai3@...wei.com>
> 
> Signed-off-by: Li Lingfeng <lilingfeng3@...wei.com>
> ---
>   drivers/md/md.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 9bdd57324c37..3b38a565bffa 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -2562,7 +2562,7 @@ static void md_kick_rdev_from_array(struct md_rdev *rdev)
>   	list_del_rcu(&rdev->same_set);
>   	pr_debug("md: unbind<%pg>\n", rdev->bdev);
>   	mddev_destroy_serial_pool(rdev->mddev, rdev);
> -	rdev->mddev = NULL;
> +	WRITE_ONCE(rdev->mddev, NULL);
>   	sysfs_remove_link(&rdev->kobj, "block");
>   	sysfs_put(rdev->sysfs_state);
>   	sysfs_put(rdev->sysfs_unack_badblocks);
> @@ -3646,7 +3646,7 @@ rdev_attr_store(struct kobject *kobj, struct attribute *attr,
>   	struct kernfs_node *kn = NULL;
>   	bool suspend = false;
>   	ssize_t rv;
> -	struct mddev *mddev = rdev->mddev;
> +	struct mddev *mddev = READ_ONCE(rdev->mddev);
>   
>   	if (!entry->store)
>   		return -EIO;
>