On Mon, Apr 12, 2021 at 6:31 PM Eric Dumazet <eduma...@google.com> wrote: > > On Mon, Apr 12, 2021 at 6:28 PM Linus Torvalds > <torva...@linux-foundation.org> wrote: > > > > On Sun, Apr 11, 2021 at 10:14 PM Guenter Roeck <li...@roeck-us.net> wrote: > > > > > > Qemu test results: > > > total: 460 pass: 459 fail: 1 > > > Failed tests: > > > sh:rts7751r2dplus_defconfig:ata:net,virtio-net:rootfs > > > > > > The failure bisects to commit 0f6925b3e8da ("virtio_net: Do not pull > > > payload in > > > skb->head"). It is a spurious problem - the test passes roughly every > > > other > > > time. When the failure is seen, udhcpc fails to get an IP address and > > > aborts > > > with SIGTERM. So far I have only seen this with the "sh" architecture. > > > > Hmm. Let's add in some more of the people involved in that commit, and > > also netdev. > > > > Nothing in there looks like it should have any interaction with > > architecture, so that "it happens on sh" sounds odd, but maybe it's > > some particular interaction with the qemu environment. > > Yes, maybe. > > I spent few hours on this, and suspect a buggy memcpy() implementation > on SH, but this was not conclusive. > > By pulling one extra byte, the problem goes away. > > Strange thing is that the udhcpc process does not go past sendto().
This is the patch working around the issue. Unfortunately I was not able to root-cause it (I really suspect something on SH) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 0824e6999e49957f7aaf7c990f6259792d42f32b..fd890a951beea03bdf24406809042666eb972655 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -408,11 +408,17 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, /* Copy all frame if it fits skb->head, otherwise * we let virtio_net_hdr_to_skb() and GRO pull headers as needed. + * + * Apparently, pulling only the Ethernet Header triggers a bug on qemu-system-sh4. + * Since GRO aggregation really cares of IPv4/IPv6, pull 20 bytes + * more to work around this bug : These 20 bytes can not belong + * to UDP/TCP payload. + * As a bonus, this makes GRO slightly faster for IPv4 (one less copy). */ if (len <= skb_tailroom(skb)) copy = len; else - copy = ETH_HLEN + metasize; + copy = ETH_HLEN + sizeof(struct iphdr) + metasize; skb_put_data(skb, p, copy); if (metasize) {