=============================
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.5.823/7802:
#0: ffffffff8c31f360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#1: ffff888024aa6148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
#2: ffff888024aa6108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
#2: ffff888024aa6108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
#3: ffffffff8c31f360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
stack backtrace:
CPU: 1 PID: 7802 Comm: syz.5.823 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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:1125
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:5154
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:exit_to_user_mode_loop+0x40/0x130 kernel/entry/common.c:168
Code: fb eb 1d e8 72 11 56 08 65 48 8b 05 fa f6 9a 7e 4c 8b 30 41 f7 c6 0e 30 02 00 0f 84 ed 00 00 00 e8 75 fc 17 00 fb 41 f6 c6 08 <74> 05 e8 b9 43 5e 08 41 f7 c6 00 10 00 00 74 08 48 89 df e8 f8 6c
RSP: 0000:ffffc900033fff10 EFLAGS: 00000246
RAX: 893f0eadc3346f00 RBX: ffffc900033fff58 RCX: 893f0eadc3346f00
RDX: dffffc0000000000 RSI: ffffffff8a2b3180 RDI: ffffffff8a7a09c0
RBP: 0000000000000000 R08: ffffffff8f0ed048 R09: ffffffff8f0ed058
R10: ffffffff8f0ed050 R11: ffffffff8f0ed043 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000004 R15: ffff88807ad63b80
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
irqentry_exit_to_user_mode+0x5/0x30 kernel/entry/common.c:320
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0033:0x7f7e1fbe64a0
Code: fe c6 44 24 0e 01 45 31 ed 45 31 f6 89 7c 24 08 85 c0 0f 84 10 01 00 00 66 90 48 8b 3c 24 49 8b 54 24 40 4c 89 f0 4a 03 14 ef <80> 3d 01 69 3a 00 00 49 89 d6 48 89 d3 74 28 25 ff 0f 00 00 83 f0
RSP: 002b:00007fff1565ad50 EFLAGS: 00000286
RAX: ffffffff817f73dd RBX: ffffffff817f7549 RCX: ffffffff817f7549
RDX: ffffffff817f7422 RSI: ffffffff817f7549 RDI: 00007f7e1f372008
RBP: 0000000000000245 R08: 00007f7e1ff75000 R09: 00007f7e1ff77000
R10: 00000000817f754d R11: 000000000000000b R12: 00007f7e1ff8b128
R13: 0000000000034dff R14: ffffffff817f73dd R15: 00007f7e20aba720
----------------
Code disassembly (best guess):
0: fb sti
1: eb 1d jmp 0x20
3: e8 72 11 56 08 call 0x856117a
8: 65 48 8b 05 fa f6 9a mov %gs:0x7e9af6fa(%rip),%rax # 0x7e9af70a
f: 7e
10: 4c 8b 30 mov (%rax),%r14
13: 41 f7 c6 0e 30 02 00 test $0x2300e,%r14d
1a: 0f 84 ed 00 00 00 je 0x10d
20: e8 75 fc 17 00 call 0x17fc9a
25: fb sti
26: 41 f6 c6 08 test $0x8,%r14b
* 2a: 74 05 je 0x31 <-- trapping instruction
2c: e8 b9 43 5e 08 call 0x85e43ea
31: 41 f7 c6 00 10 00 00 test $0x1000,%r14d
38: 74 08 je 0x42
3a: 48 89 df mov %rbx,%rdi
3d: e8 .byte 0xe8
3e: f8 clc
3f: 6c insb (%dx),%es:(%rdi)