=============================
WARNING: suspicious RCU usage
5.15.189-syzkaller #0 Not tainted
-----------------------------
net/sched/sch_api.c:304 suspicious rcu_dereference_protected() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
6 locks held by syz.4.232/5081:
#0: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
#1: ffffc90000dd0be0 ((&d->timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
#1: ffffc90000dd0be0 ((&d->timer)){+.-.}-{0:0}, at: call_timer_fn+0xbb/0x530 kernel/time/timer.c:1441
#2: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
#3: ffffffff8c11c3c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
#4: ffff8880609c9108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
#4: ffff8880609c9108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline]
#4: ffff8880609c9108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xb8a/0x2ed0 net/core/dev.c:4253
#5: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
stack backtrace:
CPU: 1 PID: 5081 Comm: syz.4.232 Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
qdisc_lookup+0xa6/0x650 net/sched/sch_api.c:304
qdisc_tree_reduce_backlog+0x190/0x430 net/sched/sch_api.c:793
cake_drop net/sched/sch_cake.c:1611 [inline]
cake_enqueue+0x3769/0x7ee0 net/sched/sch_cake.c:1945
qdisc_enqueue include/net/sch_generic.h:832 [inline]
sfb_enqueue+0x9e0/0x17d0 net/sched/sch_sfb.c:405
dev_qdisc_enqueue+0x48/0x210 net/core/dev.c:3852
__dev_xmit_skb net/core/dev.c:3936 [inline]
__dev_queue_xmit+0xd7e/0x2ed0 net/core/dev.c:4253
tipc_l2_send_msg+0x30a/0x3c0 net/tipc/bearer.c:518
tipc_bearer_xmit_skb+0x292/0x3c0 net/tipc/bearer.c:577
tipc_disc_timeout+0x568/0x6b0 net/tipc/discover.c:338
call_timer_fn+0x16c/0x530 kernel/time/timer.c:1451
expire_timers kernel/time/timer.c:1496 [inline]
__run_timers+0x525/0x7c0 kernel/time/timer.c:1767
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
handle_softirqs+0x328/0x820 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:659
irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:native_save_fl arch/x86/include/asm/irqflags.h:29 [inline]
RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:70 [inline]
RIP: 0010:arch_local_irq_save arch/x86/include/asm/irqflags.h:106 [inline]
RIP: 0010:lock_release+0x135/0x870 kernel/locking/lockdep.c:5639
Code: 03 42 0f b6 04 28 84 c0 0f 85 28 05 00 00 41 83 3e 00 0f 85 58 04 00 00 48 89 5c 24 18 48 c7 84 24 a0 00 00 00 00 00 00 00 9c <8f> 84 24 a0 00 00 00 48 8b 84 24 a0 00 00 00 48 89 44 24 50 fa 48
RSP: 0018:ffffc90002f0f598 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff88801d919dc0 RCX: 31119ef21de9f800
RDX: 0000000000000000 RSI: ffffffff8a599320 RDI: ffffffff8a5992e0
RBP: ffffc90002f0f6c0 R08: dffffc0000000000 R09: fffffbfff1ad2dd6
R10: fffffbfff1ad2dd6 R11: 1ffffffff1ad2dd5 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff88801d91a8ac R15: 1ffff920005e1ec0
rcu_read_unlock include/linux/rcupdate.h:772 [inline]
sk_filter_trim_cap+0x59c/0x810 net/core/filter.c:157
sk_filter include/linux/filter.h:915 [inline]
unix_dgram_sendmsg+0xae8/0x1890 net/unix/af_unix.c:1840
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
____sys_sendmsg+0x5a2/0x8c0 net/socket.c:2436
___sys_sendmsg+0x1f0/0x260 net/socket.c:2490
__sys_sendmmsg+0x27c/0x4a0 net/socket.c:2576
__do_sys_sendmmsg net/socket.c:2605 [inline]
__se_sys_sendmmsg net/socket.c:2602 [inline]
__x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2602
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: 0033:0x7f21a567abe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f21a38e2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f21a58a1fa0 RCX: 00007f21a567abe9
RDX: 0000000000000651 RSI: 0000200000000000 RDI: 0000000000000006
RBP: 00007f21a56fde19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f21a58a2038 R14: 00007f21a58a1fa0 R15: 00007ffeb2b95c08
----------------
Code disassembly (best guess):
0: 03 42 0f add 0xf(%rdx),%eax
3: b6 04 mov $0x4,%dh
5: 28 84 c0 0f 85 28 05 sub %al,0x528850f(%rax,%rax,8)
c: 00 00 add %al,(%rax)
e: 41 83 3e 00 cmpl $0x0,(%r14)
12: 0f 85 58 04 00 00 jne 0x470
18: 48 89 5c 24 18 mov %rbx,0x18(%rsp)
1d: 48 c7 84 24 a0 00 00 movq $0x0,0xa0(%rsp)
24: 00 00 00 00 00
29: 9c pushf
* 2a: 8f 84 24 a0 00 00 00 pop 0xa0(%rsp) <-- trapping instruction
31: 48 8b 84 24 a0 00 00 mov 0xa0(%rsp),%rax
38: 00
39: 48 89 44 24 50 mov %rax,0x50(%rsp)
3e: fa cli
3f: 48 rex.W