Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH][next] dmaengine: ti: k3-udma: Use struct_size() in
 kzalloc()
To:     "Gustavo A. R. Silva" <gustavoars@kernel.org>
CC:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Vinod Koul <vkoul@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        <dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20200619224334.GA7857@embeddedor>
 <20200624055535.GX2324254@vkoul-mobl>
 <3a5514c9-d966-c332-84ba-f418c26fa74c@embeddedor.com>
 <98426221-8bff-25df-a062-9ec1ca4e8f26@ti.com>
 <20200626132944.GA26003@embeddedor>
From:   Peter Ujfalusi <peter.ujfalusi@ti.com>
Message-ID: <04a5fb89-37eb-2cf7-d085-aaa4c9ed284d@ti.com>
Date:   Mon, 29 Jun 2020 09:43:26 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.9.0
MIME-Version: 1.0
In-Reply-To: <20200626132944.GA26003@embeddedor>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 26/06/2020 16.29, Gustavo A. R. Silva wrote:
> Hi Peter,
>=20
> Please, see my comments below...
>=20
> On Fri, Jun 26, 2020 at 10:30:37AM +0300, Peter Ujfalusi wrote:
>>
>>
>> On 24/06/2020 20.12, Gustavo A. R. Silva wrote:
>>> Hi Vinod,
>>>
>>> On 6/24/20 00:55, Vinod Koul wrote:
>>>> On 19-06-20, 17:43, Gustavo A. R. Silva wrote:
>>>>> Make use of the struct_size() helper instead of an open-coded versi=
on
>>>>> in order to avoid any potential type mistakes.
>>>>>
>>>>> This code was detected with the help of Coccinelle and, audited and=

>>>>> fixed manually.
>>>>>
>>>>> Addresses-KSPP-ID: https://github.com/KSPP/linux/issues/83
>>>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>>>> ---
>>>>>  drivers/dma/ti/k3-udma.c | 4 ++--
>>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/dma/ti/k3-udma.c b/drivers/dma/ti/k3-udma.c
>>>>> index 0d5fb154b8e2..411c54b86ba8 100644
>>>>> --- a/drivers/dma/ti/k3-udma.c
>>>>> +++ b/drivers/dma/ti/k3-udma.c
>>>>> @@ -2209,7 +2209,7 @@ udma_prep_slave_sg_pkt(struct udma_chan *uc, =
struct scatterlist *sgl,
>>>>>  	u32 ring_id;
>>>>>  	unsigned int i;
>>>>> =20
>>>>> -	d =3D kzalloc(sizeof(*d) + sglen * sizeof(d->hwdesc[0]), GFP_NOWA=
IT);
>>>>> +	d =3D kzalloc(struct_size(d, hwdesc, sglen), GFP_NOWAIT);
>>>>
>>>> struct_size() is a * b + c but here we need, a + b * c.. the trailin=
g
>>>> struct is N times here..
>>>>
>>>
>>> struct_size() works exactly as expected in this case. :)
>>> Please, see:
>>>
>>> include/linux/overflow.h:314:
>>> 314 #define struct_size(p, member, count)                            =
       \
>>> 315         __ab_c_size(count,                                       =
       \
>>> 316                     sizeof(*(p)->member) + __must_be_array((p)->m=
ember),\
>>> 317                     sizeof(*(p)))
>>
>> True, struct_size is for this sort of things.
>>
>> Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>>
>> While looking it up in include/linux/overflow.h I have noticed your
>> commit in linux-next, which adds flex_array_size()
>>
>> The example in the commit message contradicts with what the helper
>=20
> There is no contradiction here.
>=20
>> does imho. To be correct it should have been:
>>
>> struct something {
>> 	size_t count;
>> 	struct foo items[];
>> };
>>
>> - struct something *instance;
>> + struct something instance;
>>
>> - instance =3D kmalloc(struct_size(instance, items, count), GFP_KERNEL=
);
>> + instance.items =3D kmalloc(struct_size(instance, items, count), GFP_=
KERNEL);
>> instance->count =3D count;
>> memcpy(instance->items, src, flex_array_size(instance, items, instance=
->count));
>>
>=20
> This is all wrong. Please, double check how struct_size() works.

Yes, I got it mixed up, I know how struct_size works... For some reason
I just overlooked it's use in the kmalloc().

>=20
> Thanks
> --
> Gustavo
>=20
>>>>>  	if (!d)
>>>>>  		return NULL;
>>>>> =20
>>>>> @@ -2525,7 +2525,7 @@ udma_prep_dma_cyclic_pkt(struct udma_chan *uc=
, dma_addr_t buf_addr,
>>>>>  	if (period_len >=3D SZ_4M)
>>>>>  		return NULL;
>>>>> =20
>>>>> -	d =3D kzalloc(sizeof(*d) + periods * sizeof(d->hwdesc[0]), GFP_NO=
WAIT);
>>>>> +	d =3D kzalloc(struct_size(d, hwdesc, periods), GFP_NOWAIT);
>>>>>  	if (!d)
>>>>>  		return NULL;
>>>>> =20
>>>>> --=20
>>>>> 2.27.0
>>>>
>>
>> - P=C3=A9ter
>>
>> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunn=
us/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
>>

- P=C3=A9ter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki