Re: [PATCH v2 net] ptr_ring: disable KCSAN warnings

[Jason Wang <jasowang@redhat.com>]

On Thu, Mar 26, 2026 at 1:36 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> Eric Dumazet reported KCSAN warnings:
>
> BUG: KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue
>
> write to 0xffff88811d5ccc00 of 8 bytes by interrupt on cpu 0:
> __ptr_ring_zero_tail include/linux/ptr_ring.h:259 [inline]
> __ptr_ring_discard_one include/linux/ptr_ring.h:291 [inline]
> __ptr_ring_consume include/linux/ptr_ring.h:311 [inline]
> __skb_array_consume include/linux/skb_array.h:98 [inline]
> pfifo_fast_dequeue+0x770/0x8f0 net/sched/sch_generic.c:770
> dequeue_skb net/sched/sch_generic.c:297 [inline]
> qdisc_restart net/sched/sch_generic.c:402 [inline]
> __qdisc_run+0x189/0xc80 net/sched/sch_generic.c:420
> qdisc_run include/net/pkt_sched.h:120 [inline]
> net_tx_action+0x379/0x590 net/core/dev.c:5793
> handle_softirqs+0xb9/0x280 kernel/softirq.c:622
> do_softirq+0x45/0x60 kernel/softirq.c:523
> __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
> local_bh_enable include/linux/bottom_half.h:33 [inline]
> bpf_test_run+0x2db/0x620 net/bpf/test_run.c:426
> bpf_prog_test_run_skb+0x9a4/0xef0 net/bpf/test_run.c:1159
> bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4721
> __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246
> __do_sys_bpf kernel/bpf/syscall.c:6341 [inline]
> __se_sys_bpf kernel/bpf/syscall.c:6339 [inline]
> __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339
> x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> read to 0xffff88811d5ccc00 of 8 bytes by task 22632 on cpu 1:
> __ptr_ring_produce include/linux/ptr_ring.h:106 [inline]
> ptr_ring_produce include/linux/ptr_ring.h:129 [inline]
> skb_array_produce include/linux/skb_array.h:44 [inline]
> pfifo_fast_enqueue+0xd5/0x2c0 net/sched/sch_generic.c:741
> dev_qdisc_enqueue net/core/dev.c:4144 [inline]
> __dev_xmit_skb net/core/dev.c:4188 [inline]
> __dev_queue_xmit+0x6a4/0x1f20 net/core/dev.c:4795
> dev_queue_xmit include/linux/netdevice.h:3384 [inline]
> __bpf_tx_skb net/core/filter.c:2153 [inline]
> __bpf_redirect_common net/core/filter.c:2197 [inline]
> __bpf_redirect+0x862/0x990 net/core/filter.c:2204
> ____bpf_clone_redirect net/core/filter.c:2487 [inline]
> bpf_clone_redirect+0x20c/0x290 net/core/filter.c:2450
> bpf_prog_53f18857bc887b09+0x22/0x2a
> bpf_dispatcher_nop_func include/linux/bpf.h:1402 [inline]
> __bpf_prog_run include/linux/filter.h:723 [inline]
> bpf_prog_run include/linux/filter.h:730 [inline]
> bpf_test_run+0x29d/0x620 net/bpf/test_run.c:423
> bpf_prog_test_run_skb+0x9a4/0xef0 net/bpf/test_run.c:1159
> bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4721
> __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246
> __do_sys_bpf kernel/bpf/syscall.c:6341 [inline]
> __se_sys_bpf kernel/bpf/syscall.c:6339 [inline]
> __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339
> x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> value changed: 0xffff888104a93a00 -> 0x0000000000000000
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 UID: 0 PID: 22632 Comm: syz.0.4135 Tainted: G W syzkaller #0
> PREEMPT(full)
> Tainted: [W]=WARN
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/24/2026
>
> There is no race on ring accesses: reading/writing a partial pointer
> would be fine, because the reading is done by the producer
> which merely cares about NULL/non NULL.
> Document and disable the warnings using data_race().
>
> Tested-by: Opus Sonnet 4.6 1M window.
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks