linux-kernel - Re: [PATCH v2] null_blk: fix null-ptr-dereference while configuring 'power' and 'submit

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Date: Sun, 26 May 2024 14:57:07 +0200
From: Markus Elfring <Markus.Elfring@....de>
To: Yu Kuai <yukuai3@...wei.com>, linux-block@...r.kernel.org,
 kernel-janitors@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
 Chaitanya Kulkarni <kch@...dia.com>,
 Chengming Zhou <zhouchengming@...edance.com>,
 Damien Le Moal <dlemoal@...nel.org>, Hannes Reinecke <hare@...e.de>,
 Jens Axboe <axboe@...nel.dk>, Johannes Thumshirn
 <johannes.thumshirn@....com>, Yi Zhang <yi.zhang@...hat.com>,
 Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: LKML <linux-kernel@...r.kernel.org>, Yang Erkun <yangerkun@...wei.com>,
 Yi Zhang <yi.zhang@...wei.com>, Yu Kuai <yukuai1@...weicloud.com>
Subject: Re: [PATCH v2] null_blk: fix null-ptr-dereference while configuring
 'power' and 'submit_queues'

…
> 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 an instance has been configured")
…
> +++ 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 = nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues);
> +	mutex_unlock(&lock);
> +
> +	return ret;
>  }
…

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#L124

Will development interests grow for the usage of a statement like “guard(mutex)(&lock);”?

Regards,
Markus