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Subject: Re: [PATCH] nbd: Fix NULL pointer in flush_workqueue
To:     Markus Elfring <Markus.Elfring@web.de>,
        <linux-block@vger.kernel.org>, <nbd@other.debian.org>
CC:     <linux-kernel@vger.kernel.org>, <kernel-janitors@vger.kernel.org>,
        "Jens Axboe" <axboe@kernel.dk>, Josef Bacik <josef@toxicpanda.com>
References: <20210128074153.1633374-1-sunke32@huawei.com>
 <1739e522-5980-f86e-cb90-19b61539a5cf@web.de>
From:   Sun Ke <sunke32@huawei.com>
Message-ID: <28c83b00-7d0b-ee0d-640b-017c9f8410eb@huawei.com>
Date:   Mon, 1 Feb 2021 14:43:00 +0800
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hi，Markus

在 2021/1/29 3:42, Markus Elfring 写道:
> …
>> +++ b/drivers/block/nbd.c
>> @@ -2011,12 +2011,20 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
>>   		       index);
>>   		return -EINVAL;
>>   	}
>> +	mutex_lock(&nbd->config_lock);
>>   	if (!refcount_inc_not_zero(&nbd->refs)) {
>>   		mutex_unlock(&nbd_index_mutex);
>> +		mutex_unlock(&nbd->config_lock);
> Can an other function call order become relevant for the unlocking of these mutexes?
Do you think the nbd->config_lock  mutex here is useless?
>
>
>>   		printk(KERN_ERR "nbd: device at index %d is going down\n",
>>   		       index);
> May such an error message be moved into the lock scope?
Sure.
>
>
>>   		return -EINVAL;
>>   	}
>> +	if (!nbd->recv_workq) {
>> +		mutex_unlock(&nbd->config_lock);
>> +		mutex_unlock(&nbd_index_mutex);
>> +		return -EINVAL;
>> +	}
> How do you think about to connect the code from this if branch
> with a jump target like “unlock” so that such statements would be shareable
> for the desired exception handling?
OK, I will improve it in V2 patch.
>
>
>> +	mutex_unlock(&nbd->config_lock);
>>   	mutex_unlock(&nbd_index_mutex);
>>   	if (!refcount_inc_not_zero(&nbd->config_refs)) {
>>   		nbd_put(nbd);
>
> Regards,
> Markus
> .