[syzbot] [net?] KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (6)

[syzbot <syzbot+b44f2bbe286b9355c563@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    37a93dd5c49b Merge tag 'net-next-7.0' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1244fa52580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ec543385a37b9f17
dashboard link: https://syzkaller.appspot.com/bug?extid=b44f2bbe286b9355c563
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5c78f22cfb6c/disk-37a93dd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/77c2f419bced/vmlinux-37a93dd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5640d838c887/bzImage-37a93dd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b44f2bbe286b9355c563@syzkaller.appspotmail.com

==================================================================
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
==================================================================


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