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[73.241.150.58]) by smtp.gmail.com with ESMTPSA id v10sm6321590pff.192.2020.08.10.08.06.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Aug 2020 08:06:12 -0700 (PDT) Subject: Re: [PATCH] net: eliminate meaningless memcpy to data in pskb_carve_inside_nonlinear() To: Miaohe Lin , davem@davemloft.net, kuba@kernel.org, pshelar@ovn.org, martin.varghese@nokia.com, fw@strlen.de, dcaratti@redhat.com, edumazet@google.com, steffen.klassert@secunet.com, pabeni@redhat.com, shmulik@metanetworks.com, kyk.segfault@gmail.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200810122856.5423-1-linmiaohe@huawei.com> From: Eric Dumazet Message-ID: Date: Mon, 10 Aug 2020 08:06:11 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200810122856.5423-1-linmiaohe@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/10/20 5:28 AM, Miaohe Lin wrote: > The skb_shared_info part of the data is assigned in the following loop. It > is meaningless to do a memcpy here. > > Signed-off-by: Miaohe Lin > --- > net/core/skbuff.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 7e2e502ef519..5b983c9472f5 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -5952,9 +5952,6 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, > > size = SKB_WITH_OVERHEAD(ksize(data)); > > - memcpy((struct skb_shared_info *)(data + size), > - skb_shinfo(skb), offsetof(struct skb_shared_info, > - frags[skb_shinfo(skb)->nr_frags])); > if (skb_orphan_frags(skb, gfp_mask)) { > kfree(data); > return -ENOMEM; > Reminder : net-next is CLOSED. This is not correct. We still have to copy _something_ Something like : diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 2828f6d5ba898a5e50ccce45589bf1370e474b0f..1c0519426c7ba4b04377fc8054c4223c135879ab 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -5953,8 +5953,8 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, size = SKB_WITH_OVERHEAD(ksize(data)); memcpy((struct skb_shared_info *)(data + size), - skb_shinfo(skb), offsetof(struct skb_shared_info, - frags[skb_shinfo(skb)->nr_frags])); + skb_shinfo(skb), offsetof(struct skb_shared_info, frags[0])); + if (skb_orphan_frags(skb, gfp_mask)) { kfree(data); return -ENOMEM;