=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
include/net/neighbour.h:286 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.4.249/5174:
 #0: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313

stack backtrace:
CPU: 1 PID: 5174 Comm: syz.4.249 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 ___neigh_lookup_noref include/net/neighbour.h:286 [inline]
 __ipv4_neigh_lookup_noref+0x376/0x420 include/net/arp.h:27
 bpf_ipv4_fib_lookup+0xc8a/0x1310 net/core/filter.c:5703
 ____bpf_xdp_fib_lookup net/core/filter.c:5873 [inline]
 bpf_xdp_fib_lookup+0x17c/0x1c0 net/core/filter.c:5861
 bpf_prog_744adbbd36285891+0x3e/0xa48
 __bpf_prog_run include/linux/filter.h:621 [inline]
 bpf_prog_run_xdp include/linux/filter.h:830 [inline]
 bpf_test_run+0x567/0x800 net/bpf/test_run.c:117
 bpf_prog_test_run_xdp+0x3e8/0x910 net/bpf/test_run.c:821
 bpf_prog_test_run+0x31c/0x390 kernel/bpf/syscall.c:3374
 __sys_bpf+0x5a5/0x6f0 kernel/bpf/syscall.c:4675
 __do_sys_bpf kernel/bpf/syscall.c:4761 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:4759 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4759
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f57c0301e99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f57be55a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f57c0589fa0 RCX: 00007f57c0301e99
RDX: 0000000000000050 RSI: 0000200000000700 RDI: 000000000000000a
RBP: 00007f57c0397eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f57c058a038 R14: 00007f57c0589fa0 R15: 00007ffe051e4f68
 </TASK>

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
include/net/neighbour.h:291 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.4.249/5174:
 #0: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313

stack backtrace:
CPU: 1 PID: 5174 Comm: syz.4.249 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 ___neigh_lookup_noref include/net/neighbour.h:291 [inline]
 __ipv4_neigh_lookup_noref+0x39f/0x420 include/net/arp.h:27
 bpf_ipv4_fib_lookup+0xc8a/0x1310 net/core/filter.c:5703
 ____bpf_xdp_fib_lookup net/core/filter.c:5873 [inline]
 bpf_xdp_fib_lookup+0x17c/0x1c0 net/core/filter.c:5861
 bpf_prog_744adbbd36285891+0x3e/0xa48
 __bpf_prog_run include/linux/filter.h:621 [inline]
 bpf_prog_run_xdp include/linux/filter.h:830 [inline]
 bpf_test_run+0x567/0x800 net/bpf/test_run.c:117
 bpf_prog_test_run_xdp+0x3e8/0x910 net/bpf/test_run.c:821
 bpf_prog_test_run+0x31c/0x390 kernel/bpf/syscall.c:3374
 __sys_bpf+0x5a5/0x6f0 kernel/bpf/syscall.c:4675
 __do_sys_bpf kernel/bpf/syscall.c:4761 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:4759 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4759
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f57c0301e99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f57be55a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f57c0589fa0 RCX: 00007f57c0301e99
RDX: 0000000000000050 RSI: 0000200000000700 RDI: 000000000000000a
RBP: 00007f57c0397eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f57c058a038 R14: 00007f57c0589fa0 R15: 00007ffe051e4f68
 </TASK>