=============================
WARNING: suspicious RCU usage
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
4 locks held by syz.1.219/4953:
#0: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#1: ffff88801f787948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5128
#2: ffff88801f787908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
#2: ffff88801f787908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
#3: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
stack backtrace:
CPU: 1 PID: 4953 Comm: syz.1.219 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
dump_stack_lvl+0x188/0x250 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:783
cake_dequeue+0x1bd6/0x4b10 net/sched/sch_cake.c:2205
qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1115
tbf_dequeue+0x7d/0xce0 net/sched/sch_tbf.c:265
dequeue_skb net/sched/sch_generic.c:295 [inline]
qdisc_restart net/sched/sch_generic.c:400 [inline]
__qdisc_run+0x236/0x1490 net/sched/sch_generic.c:418
qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:131
net_tx_action+0x6d9/0x880 net/core/dev.c:5128
handle_softirqs+0x339/0x830 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x13b/0x230 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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 4e 2c 98 f7 48 89 df e8 86 04 99 f7 e8 11 f3 b9 f7 fb bf 01 00 00 00 06 0b 8d f7 65 8b 05 87 17 3d 76 85 c0 74 02 5b c3 e8 d4 24 3b
RSP: 0018:ffffc90003867bc0 EFLAGS: 00000282
RAX: e0342999e94dd800 RBX: ffff888075d40000 RCX: e0342999e94dd800
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff888075d40003 R09: 1ffff1100eba8000
R10: dffffc0000000000 R11: ffffed100eba8001 R12: ffff888075d40000
R13: 0000000000000021 R14: dffffc0000000000 R15: 000000001c000004
spin_unlock_irq include/linux/spinlock.h:414 [inline]
get_signal+0x11d6/0x12c0 kernel/signal.c:2903
arch_do_signal_or_restart+0xe7/0x12c0 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f7e7a277cb8
Code: 89 01 eb 91 48 8b 54 24 08 48 8d 35 fb 29 1b 00 48 8d 3d fe 29 1b 00 31 c0 e8 24 d1 ff ff 0f 1f 40 00 53 48 8b 1d e8 40 3c 00 <45> 31 d2 31 c9 48 8b 17 45 31 db 4c 8d 83 00 00 40 00 48 89 d0 0f
RSP: 002b:00007ffc76041e50 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000001b31120000 RCX: 00007f7e7a3becb9
RDX: ffffffffffffffff RSI: 0000000000000080 RDI: 00007f7e7a639fb0
RBP: 00007f7e7a639fb0 R08: 00007f7e7a639fa0 R09: 0000000000000000
R10: 00007ffc76041fb0 R11: 0000000000000246 R12: 00007f7e7a639fa0
R13: 0000200000000000 R14: 00007ffc76041e68 R15: 00007f7e7a639fa0
----------------
Code disassembly (best guess):
0: 00 00 add %al,(%rax)
2: 00 66 90 add %ah,-0x70(%rsi)
5: 53 push %rbx
6: 48 89 fb mov %rdi,%rbx
9: 48 83 c7 18 add $0x18,%rdi
d: 48 8b 74 24 08 mov 0x8(%rsp),%rsi
12: e8 4e 2c 98 f7 call 0xf7982c65
17: 48 89 df mov %rbx,%rdi
1a: e8 86 04 99 f7 call 0xf79904a5
1f: e8 11 f3 b9 f7 call 0xf7b9f335
24: fb sti
25: bf 01 00 00 00 mov $0x1,%edi
* 2a: e8 06 0b 8d f7 call 0xf78d0b35 <-- trapping instruction
2f: 65 8b 05 87 17 3d 76 mov %gs:0x763d1787(%rip),%eax # 0x763d17bd
36: 85 c0 test %eax,%eax
38: 74 02 je 0x3c
3a: 5b pop %rbx
3b: c3 ret
3c: e8 .byte 0xe8
3d: d4 (bad)
3e: 24 3b and $0x3b,%al