linux-kernel - Re: [PATCH] net: dsa: loop: Check for memory allocation failure

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Message-ID: <f9058de7-ef9e-f6eb-751d-72ffdce512bb@gmail.com>
Date:   Mon, 8 May 2017 17:35:09 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Julia Lawall <julia.lawall@...6.fr>, Joe Perches <joe@...ches.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        'Christophe JAILLET' <christophe.jaillet@...adoo.fr>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "vivien.didelot@...oirfairelinux.com" 
        <vivien.didelot@...oirfairelinux.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] net: dsa: loop: Check for memory allocation failure

On 05/08/2017 04:46 PM, Julia Lawall wrote:
> 
> 
> On Mon, 8 May 2017, Joe Perches wrote:
> 
>> On Mon, 2017-05-08 at 20:32 +0800, Julia Lawall wrote:
>>>
>>> On Mon, 8 May 2017, David Laight wrote:
>>>
>>>> From: Christophe JAILLET
>>>>> Sent: 06 May 2017 06:30
>>>>> If 'devm_kzalloc' fails, a NULL pointer will be dereferenced.
>>>>> Return -ENOMEM instead, as done for some other memory allocation just a
>>>>> few lines above.
>>>>
>>>> ...
>>>>> --- a/drivers/net/dsa/dsa_loop.c
>>>>> +++ b/drivers/net/dsa/dsa_loop.c
>>>>> @@ -256,6 +256,9 @@ static int dsa_loop_drv_probe(struct mdio_device *mdiodev)
>>>>>  		return -ENOMEM;
>>>>>
>>>>>  	ps = devm_kzalloc(&mdiodev->dev, sizeof(*ps), GFP_KERNEL);
>>>>> +	if (!ps)
>>>>> +		return -ENOMEM;
>>>>> +
>>>>>  	ps->netdev = dev_get_by_name(&init_net, pdata->netdev);
>>>>>  	if (!ps->netdev)
>>>>>  		return -EPROBE_DEFER;
>>>>
>>>> On the face if it this code leaks like a sieve.
>>>
>>> I don't think so.  The allocations (dsa_switch_alloc and devm_kzalloc) use
>>> devm functions.
>>
>> It's at least wasteful.
>>
>> Each time -EPROBE_DEFER occurs, another set of calls to
>> dsa_switch_alloc and dev_kzalloc also occurs.
>>
>> Perhaps it'd be better to do:
>>
>> 	if (ps->netdev) {
>> 		devm_kfree(&devmdev->dev, ps);
>> 		devm_kfree(&mdiodev->dev, ds);
>> 		return -EPROBE_DEFER;
>> 	}
> 
> Is EPROBE_DEFER handled differently than other kinds of errors?

In the core device driver model, yes, EPROBE_DEFER is treated
differently than other errors because it puts the driver on a retry queue.

EPROBE_DEFER is already a slow and exceptional path, and this is a
mock-up driver, so I am not sure what value there is in trying to
balance devm_kzalloc() with corresponding devm_kfree()...
-- 
Florian