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Date: Sun, 26 May 2024 14:57:07 +0200
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To: Yu Kuai <yukuai3@huawei.com>, linux-block@vger.kernel.org,
 kernel-janitors@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>,
 Chaitanya Kulkarni <kch@nvidia.com>,
 Chengming Zhou <zhouchengming@bytedance.com>,
 Damien Le Moal <dlemoal@kernel.org>, Hannes Reinecke <hare@suse.de>,
 Jens Axboe <axboe@kernel.dk>, Johannes Thumshirn
 <johannes.thumshirn@wdc.com>, Yi Zhang <yi.zhang@redhat.com>,
 Zhu Yanjun <yanjun.zhu@linux.dev>
Cc: LKML <linux-kernel@vger.kernel.org>, Yang Erkun <yangerkun@huawei.com>,
 Yi Zhang <yi.zhang@huawei.com>, Yu Kuai <yukuai1@huaweicloud.com>
References: <20240523153934.1937851-1-yukuai1@huaweicloud.com>
Subject: Re: [PATCH v2] null_blk: fix null-ptr-dereference while configuring
 'power' and 'submit_queues'
Content-Language: en-GB
From: Markus Elfring <Markus.Elfring@web.de>
In-Reply-To: <20240523153934.1937851-1-yukuai1@huaweicloud.com>
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=E2=80=A6
> Fix this problem by resuing the global mutex to protect
> nullb_device_power_store() and nullb_update_nr_hw_queues() from configfs=
.
>
> Fixes: 45919fbfe1c4 ("null_blk: Enable modifying 'submit_queues' after a=
n instance has been configured")
=E2=80=A6
> +++ b/drivers/block/null_blk/main.c
> @@ -413,13 +413,25 @@ static int nullb_update_nr_hw_queues(struct nullb_=
device *dev,
>  static int nullb_apply_submit_queues(struct nullb_device *dev,
>  				     unsigned int submit_queues)
>  {
> -	return nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues)=
;
> +	int ret;
> +
> +	mutex_lock(&lock);
> +	ret =3D nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues=
);
> +	mutex_unlock(&lock);
> +
> +	return ret;
>  }
=E2=80=A6

How do you think about to increase the application of scope-based resource=
 management here?
https://elixir.bootlin.com/linux/v6.9.1/source/include/linux/cleanup.h#L12=
4

Will development interests grow for the usage of a statement like =E2=80=
=9Cguard(mutex)(&lock);=E2=80=9D?

Regards,
Markus