From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net 1/2] tuntap: limit head length of skb allocated Date: Tue, 12 Nov 2013 09:21:12 -0500 (EST) Message-ID: <857673324.22319676.1384266072168.JavaMail.root@redhat.com> References: <1384250577-20330-1-git-send-email-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE To: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, stefanha@redhat.com Return-path: In-Reply-To: <1384250577-20330-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org ----- =E5=8E=9F=E5=A7=8B=E9=82=AE=E4=BB=B6 ----- > We currently use hdr_len as a hint of head length which is advertised= by > guest. But when guest advertise a very big value, it can lead to an 6= 4K+ > allocating of kmalloc() which has a very high possibility of failure = when > host > memory is fragmented or under heavy stress. The huge hdr_len also red= uce the > effect of zerocopy or even disable if a gso skb is linearized in gues= t. >=20 > To solves those issues, this patch introduces an upper limit (PAGE_SI= ZE) of > the > head, which guarantees an order 0 allocation each time. >=20 > Cc: Stefan Hajnoczi > Cc: Michael S. Tsirkin > Signed-off-by: Jason Wang > --- > The patch was needed for stable. > --- > drivers/net/tun.c | 5 +++++ > 1 file changed, 5 insertions(+) >=20 > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 7cb105c..5537b65 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -954,6 +954,11 @@ static struct sk_buff *tun_alloc_skb(struct tun_= file > *tfile, > struct sock *sk =3D tfile->socket.sk; > struct sk_buff *skb; > int err; > + int good_linear =3D SKB_MAX_HEAD(prepad); > + > + /* Don't use huge linear part */ > + if (linear > good_linear) > + linear =3D good_linear; > =20 > /* Under a page? Don't bother with paged skb. */ > if (prepad + len < PAGE_SIZE || !linear) > -- > 1.8.3.2 >=20 Looks like reduce the linear here will cause callers' iov_pages() under= estimation. Will send V2. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kerne= l" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >=20