On Mon, Jul 10, 2023 at 06:09:28PM -0700, Alexei Starovoitov wrote:
> On Thu, Jul 6, 2023 at 1:47 PM Maciej Fijalkowski
> <maciej.fijalkowski@xxxxxxxxx> wrote:
> >
> > Introduce new netlink attribute NETDEV_A_DEV_XDP_ZC_MAX_SEGS that will
> > carry maximum fragments that underlying ZC driver is able to handle on
> > TX side. It is going to be included in netlink response only when driver
> > supports ZC. Any value higher than 1 implies multi-buffer ZC support on
> > underlying device.
> >
> > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
>
> I suspect something in this patch makes XDP bonding test fail.
> See BPF CI.
>
> I can reproduce the failure locally as well.
> test_progs -t bond
> works without the series and fails with them.
Hi Alexei,
this fails on second bpf_xdp_query() call due to non-zero (?) contents at the
end of bpf_xdp_query_opts struct - currently it looks as following:
$ pahole -C bpf_xdp_query_opts libbpf.so
struct bpf_xdp_query_opts {
size_t sz; /* 0 8 */
__u32 prog_id; /* 8 4 */
__u32 drv_prog_id; /* 12 4 */
__u32 hw_prog_id; /* 16 4 */
__u32 skb_prog_id; /* 20 4 */
__u8 attach_mode; /* 24 1 */
/* XXX 7 bytes hole, try to pack */
__u64 feature_flags; /* 32 8 */
__u32 xdp_zc_max_segs; /* 40 4 */
/* size: 48, cachelines: 1, members: 8 */
/* sum members: 37, holes: 1, sum holes: 7 */
/* padding: 4 */
/* last cacheline: 48 bytes */
};
Fix is either to move xdp_zc_max_segs up to existing hole or to zero out
struct before bpf_xdp_query() calls, like:
memset(&query_opts, 0, sizeof(struct bpf_xdp_query_opts));
query_opts.sz = sizeof(struct bpf_xdp_query_opts);
I am kinda confused as this is happening due to two things. First off
bonding driver sets its xdp_features to NETDEV_XDP_ACT_MASK and in turn
this implies ZC feature enabled which makes xdp_zc_max_segs being included
in the response (it's value is 1 as it's the default).
Then, offsetofend(struct type, type##__last_field) that is used as one of
libbpf_validate_opts() args gives me 40 but bpf_xdp_query_opts::sz has
stored 48, so in the end we go through the last 8 bytes in
libbpf_is_mem_zeroed() and we hit the '1' from xdp_zc_max_segs.
So, (silly) questions:
- why bonding driver defaults to all features enabled?
- why __last_field does not recognize xdp_zc_max_segs at the end?
Besides, I think i'll move xdp_zc_max_segs above to the hole. This fixes
the bonding test for me.
