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Date:   Tue, 15 Jan 2019 15:11:40 -0600
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@kernel.org>,
        "David S. Miller" <davem@davemloft.net>
Cc:     linux-nfs@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH net-next] svcrdma: Use struct_size() in kmalloc()
Message-ID: <20190115211140.GA16131@embeddedor>
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Sender: linux-kernel-owner@vger.kernel.org
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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>
---
 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