linux-kernel - Re: [PATCH v2 2/7] staging: qlge: Initialize devlink health dump framework

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Date:   Thu, 15 Oct 2020 12:22:08 +0800
From:   Coiby Xu <coiby.xu@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     devel@...verdev.osuosl.org,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "supporter:QLOGIC QLGE 10Gb ETHERNET DRIVER" 
        <GR-Linux-NIC-Dev@...vell.com>,
        Manish Chopra <manishc@...vell.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shung-Hsi Yu <shung-hsi.yu@...e.com>,
        open list <linux-kernel@...r.kernel.org>,
        Benjamin Poirier <benjamin.poirier@...il.com>,
        "open list:QLOGIC QLGE 10Gb ETHERNET DRIVER" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 2/7] staging: qlge: Initialize devlink health dump
 framework

On Wed, Oct 14, 2020 at 04:08:46PM +0300, Dan Carpenter wrote:
>On Wed, Oct 14, 2020 at 06:43:01PM +0800, Coiby Xu wrote:
>>  static int qlge_probe(struct pci_dev *pdev,
>>  		      const struct pci_device_id *pci_entry)
>>  {
>>  	struct net_device *ndev = NULL;
>>  	struct qlge_adapter *qdev = NULL;
>> +	struct devlink *devlink;
>>  	static int cards_found;
>>  	int err = 0;
>>
>> -	ndev = alloc_etherdev_mq(sizeof(struct qlge_adapter),
>> +	devlink = devlink_alloc(&qlge_devlink_ops, sizeof(struct qlge_adapter));
>> +	if (!devlink)
>> +		return -ENOMEM;
>> +
>> +	qdev = devlink_priv(devlink);
>> +
>> +	ndev = alloc_etherdev_mq(sizeof(struct qlge_netdev_priv),
>>  				 min(MAX_CPUS,
>>  				     netif_get_num_default_rss_queues()));
>>  	if (!ndev)
>> -		return -ENOMEM;
>> +		goto devlink_free;
>>
>> -	err = qlge_init_device(pdev, ndev, cards_found);
>> -	if (err < 0) {
>> -		free_netdev(ndev);
>> -		return err;
>
>In the old code, if qlge_init_device() fails then it frees "ndev".
>
>> -	}
>> +	qdev->ndev = ndev;
>> +	err = qlge_init_device(pdev, qdev, cards_found);
>> +	if (err < 0)
>> +		goto devlink_free;
>
>But the patch introduces a new resource leak.

Thank you for spotting this issue!

>
>>
>> -	qdev = netdev_priv(ndev);
>>  	SET_NETDEV_DEV(ndev, &pdev->dev);
>>  	ndev->hw_features = NETIF_F_SG |
>>  		NETIF_F_IP_CSUM |
>> @@ -4611,8 +4619,14 @@ static int qlge_probe(struct pci_dev *pdev,
>>  		qlge_release_all(pdev);
>>  		pci_disable_device(pdev);
>>  		free_netdev(ndev);
>> -		return err;
>> +		goto devlink_free;
>>  	}
>> +
>> +	err = devlink_register(devlink, &pdev->dev);
>> +	if (err)
>> +		goto devlink_free;
>> +
>> +	qlge_health_create_reporters(qdev);
>>  	/* Start up the timer to trigger EEH if
>>  	 * the bus goes dead
>>  	 */
>> @@ -4623,6 +4637,10 @@ static int qlge_probe(struct pci_dev *pdev,
>>  	atomic_set(&qdev->lb_count, 0);
>>  	cards_found++;
>>  	return 0;
>> +
>> +devlink_free:
>> +	devlink_free(devlink);
>> +	return err;
>>  }
>
>The best way to write error handling code is keep tracke of the most
>recent allocation which was allocated successfully.
>
>	one = alloc();
>	if (!one)
>		return -ENOMEM;  //  <-- nothing allocated successfully
>
>	two = alloc();
>	if (!two) {
>		ret = -ENOMEM;
>		goto free_one; // <-- one was allocated successfully
>                               // Notice that the label name says what
>			       // the goto does.
>	}
>
>	three = alloc();
>	if (!three) {
>		ret = -ENOMEM;
>		goto free_two; // <-- two allocated, two freed.
>	}
>
>	...
>
>	return 0;
>
>free_two:
>	free(two);
>free_one:
>	free(one);
>
>	return ret;
>
Thank you for teaching me this pattern!

>In the old code qlge_probe() freed things before returning, and that's
>fine if there is only two allocations in the function but when there are
>three or more allocations, then use gotos to unwind.
>
>Ideally there would be a ql_deinit_device() function to mirror the
>ql_init_device() function.  The ql_init_device() is staging quality
>code with leaks and bad label names.  It should be re-written to free
>things one step at a time instead of calling ql_release_all().
>
I'll see how I can improve ql_init_device. Thank you for the suggestion!

>Anyway, let's not introduce new leaks at least.
>
>regards,
>dan carpenter

--
Best regards,
Coiby