linux-kernel - Re: [PATCH][next] dmaengine: ti: k3-udma: Use struct

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Date:   Wed, 24 Jun 2020 12:12:23 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Vinod Koul <vkoul@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     Dan Williams <dan.j.williams@...el.com>, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] dmaengine: ti: k3-udma: Use struct_size() in
 kzalloc()

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 version
>> 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@...nel.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;
>>  
>> -	d = kzalloc(sizeof(*d) + sglen * sizeof(d->hwdesc[0]), GFP_NOWAIT);
>> +	d = kzalloc(struct_size(d, hwdesc, sglen), GFP_NOWAIT);
> 
> struct_size() is a * b + c but here we need, a + b * c.. the trailing
> 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)->member),\
317                     sizeof(*(p)))
318

Thanks
--
Gustavo

>>  	if (!d)
>>  		return NULL;
>>  
>> @@ -2525,7 +2525,7 @@ udma_prep_dma_cyclic_pkt(struct udma_chan *uc, dma_addr_t buf_addr,
>>  	if (period_len >= SZ_4M)
>>  		return NULL;
>>  
>> -	d = kzalloc(sizeof(*d) + periods * sizeof(d->hwdesc[0]), GFP_NOWAIT);
>> +	d = kzalloc(struct_size(d, hwdesc, periods), GFP_NOWAIT);
>>  	if (!d)
>>  		return NULL;
>>  
>> -- 
>> 2.27.0
>