netdev - Re: [PATCH net-next] svcrdma: Use struct

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Date:   Tue, 15 Jan 2019 16:49:16 -0500
From:   Chuck Lever <chuck.lever@...cle.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Bruce Fields <bfields@...ldses.org>,
        Jeff Layton <jlayton@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] svcrdma: Use struct_size() in kmalloc()



On Jan 15, 2019, at 4:11 PM, Gustavo A. R. Silva <gustavo@...eddedor.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@...eddedor.com>

Reviewed-by: Chuck Lever <chuck.lever@...cle.com>


> ---
> 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