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

Sebastian Andrzej Siewior
2026-02-17T07:42:15Z

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