Subject: Re: [PATCH net-next] svcrdma: Use struct_size() in kmalloc()
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Bruce Fields <bfields@fieldses.org>,
        Jeff Layton <jlayton@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190115211140.GA16131@embeddedor>
 <F652FEF1-0FD7-4FFD-80D4-44DBC2FF47B5@oracle.com>
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Message-ID: <9e965c53-116d-4aad-63e9-e26264bea9d1@embeddedor.com>
Date:   Tue, 15 Jan 2019 15:53:48 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.2.1
MIME-Version: 1.0
In-Reply-To: <F652FEF1-0FD7-4FFD-80D4-44DBC2FF47B5@oracle.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


On 1/15/19 3:49 PM, Chuck Lever wrote:
> 
> 
> On Jan 15, 2019, at 4:11 PM, Gustavo A. R. Silva <gustavo@embeddedor.com> wrote:
> 
>> One of the more common cases of allocation size calculations is finding
>> the size of a structure that has a zero-sized array at the end, along
>> with memory for some number of elements for that array. For example:
>>
>> struct foo {
>>     int stuff;
>>     struct boo entry[];
>> };
>>
>> instance = kmalloc(sizeof(struct foo) + count * sizeof(struct boo), GFP_KERNEL);
>>
>> Instead of leaving these open-coded and prone to type mistakes, we can
>> now use the new struct_size() helper:
>>
>> instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
>>
>> This code was detected with the help of Coccinelle.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> 
> Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
> 

Thank you, Chuck.
--
Gustavo

> 
>> ---
>> net/sunrpc/xprtrdma/svc_rdma_rw.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
>> index dc1951759a8e..cad37c2122ab 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
>> @@ -64,8 +64,7 @@ svc_rdma_get_rw_ctxt(struct svcxprt_rdma *rdma, unsigned int sges)
>> 		spin_unlock(&rdma->sc_rw_ctxt_lock);
>> 	} else {
>> 		spin_unlock(&rdma->sc_rw_ctxt_lock);
>> -		ctxt = kmalloc(sizeof(*ctxt) +
>> -			       SG_CHUNK_SIZE * sizeof(struct scatterlist),
>> +		ctxt = kmalloc(struct_size(ctxt, rw_first_sgl, SG_CHUNK_SIZE),
>> 			       GFP_KERNEL);
>> 		if (!ctxt)
>> 			goto out;
>> -- 
>> 2.20.1
> 
> --
> Chuck Lever
> 
> 
>