Re: [PATCH bpf v3 2/2] bpf: devmap: fix race in bq_xmit_all on PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2026-02-13 11:40:15 [+0800], Jiayuan Chen wrote:
…
> timeslicing during the mdelay window causes interleaving. Without the
> fix, KASAN reports null-ptr-deref due to operating on freed frames:
> 
>   BUG: KASAN: null-ptr-deref in __build_skb_around+0x22d/0x340
>   Write of size 32 at addr 0000000000000d50 by task devmap_race_rep/449
> 
>   CPU: 0 UID: 0 PID: 449 Comm: devmap_race_rep Not tainted 6.19.0+ #31 PREEMPT_RT
>   Call Trace:
>    <TASK>
>    __build_skb_around+0x22d/0x340
>    build_skb_around+0x25/0x260
>    __xdp_build_skb_from_frame+0x103/0x860
>    veth_xdp_rcv_bulk_skb.isra.0+0x162/0x320
>    veth_xdp_rcv.constprop.0+0x61e/0xbb0
>    veth_poll+0x280/0xb50
>    __napi_poll.constprop.0+0xa5/0x590
>    net_rx_action+0x4b0/0xea0
>    handle_softirqs.isra.0+0x1b3/0x780
>    __local_bh_enable_ip+0x12a/0x240
>    xdp_test_run_batch.constprop.0+0xedd/0x1f60
>    bpf_test_run_xdp_live+0x304/0x640
>    bpf_prog_test_run_xdp+0xd24/0x1b70
>    __sys_bpf+0x61c/0x3e00
>    </TASK>
> 
>   Kernel panic - not syncing: Fatal exception in interrupt

I would move this next to the diffstat (same as with the previous
patch) since it is obvious once you described it.

Sebastian