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charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Oliver, hi Marc, since commit d4fb6514ff8e ("can: use skb hash instead of private variable in headroom") we are losing received CAN frames on raw sockets when RPS is enabled on the CAN interface=2E The problem also shows up in the stable backports (seen on [6=2E12=2E109])=2E Setup: - Kernel: 6=2E12=2E109 - Platform: OpenWrt 25=2E12=2E5, 4 CPU cores - CAN controller / driver: mcp251xfd - OpenWrt enables packet steering (RPS) by default on multi-core systems, so rps_cpus is non-zero on can0 Symptom: The application on a CAN_RAW socket misses frames=2E /proc/net/can/stats counts more RX frames than the application receives=2E With echo 0 > /sys/class/net/can0/queues/rx-0/rps_cpus the losses disappear completely=2E [Optional: rate/amount of loss, number of filters on the socket, whether join_filters is used=2E] Analysis (as far as I understand it): 1=2E RX skbs from the driver start with skb->hash =3D=3D 0=2E 2=2E With RPS enabled, get_rps_cpu() calls skb_get_hash() in the netif_rx() path before can_rcv() is reached=2E The flow dissector finds no L3/L4 headers in CAN skbs, so every CAN frame gets the same non-zero hash with sw_hash =3D 1=2E 3=2E can_set_skb_uid() only assigns a new counter value while skb->hash is 0, so the RPS hash is kept and the frame gets no unique identifier=2E 4=2E raw_rcv() treats a frame as a duplicate when both the skb pointer and skb->hash match the per-CPU uniq entry=2E Since the slab allocator often returns the same address for the next skb, a new frame with the same (constant) hash is dropped as a duplicate=2E Before d4fb6514ff8e this could not happen because the unique id was kept in can_skb_priv::skbcnt, independent of skb->hash=2E Thanks, Joerg