On Tue, Sep 9, 2025 at 9:21 AM Nimrod Oren [off-list ref] wrote:

On 05/09/2025 1:16, Amery Hung wrote:

quoted

On Thu, Aug 28, 2025 at 6:39 AM Nimrod Oren [off-list ref] wrote:

quoted

I got a crash when testing this series with the xdp_dummy program from
tools/testing/selftests/net/lib/. Need to make sure we're not breaking
compatibility for programs that keep the linear part empty.

ping.py test ran successfully for me. Is this what you tried but
crashed the kernel?

Yes, that's odd. Is it possible that the native multibuf case was
skipped over because of an older iproute2/libbpf version?

If it's helpful, I used iproute2-6.16.0 built with libbpf 1.7.0 support.
I am able to reproduce the crash by loading multibuf prog directly with:
`ip link set dev eth0 mtu 9000 xdp obj
tools/testing/selftests/net/lib/xdp_dummy.bpf.o sec xdp.frags`

I can reproduce it with v2. Will fix it in v3.

The bug is that sinfo->flags is also cleared in build_skb(), so later
xdp_buff_has_frags() will always return false and no data was ever
pulled into the linear part.