=============================
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
5 locks held by syz.4.546/6289:
#0: ffff88802601e5a0 (&u->iolock){+.+.}-{3:3}, at: __unix_dgram_recvmsg+0x205/0xd90 net/unix/af_unix.c:2312
#1: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#2: ffff888072abb148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
#3: ffff888072abb108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
#3: ffff888072abb108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
#4: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
stack backtrace:
CPU: 1 PID: 6289 Comm: syz.4.546 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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: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: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:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xbc/0x120 kernel/locking/spinlock.c:194
Code: c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f7 44 24 20 00 02 00 00 41 c6 04 07 f8 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 2f 8a 8c f7 65 8b 05 d0 97 3c 76 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc9000359f5e0 EFLAGS: 00000206
RAX: dffffc0000000004 RBX: 0000000000000a02 RCX: 5f91833ff1857800
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: 0000000000000001
RBP: ffffc9000359f678 R08: ffffffff901d4177 R09: 1ffffffff203a82e
R10: dffffc0000000000 R11: fffffbfff203a82f R12: dffffc0000000000
R13: 1ffff11004c03c44 R14: ffff88802601e1c8 R15: 1ffff920006b3ebc
spin_unlock_irqrestore include/linux/spinlock.h:419 [inline]
__skb_try_recv_datagram+0x179/0x4d0 net/core/datagram.c:267
__unix_dgram_recvmsg+0x301/0xd90 net/unix/af_unix.c:2315
____sys_recvmsg+0x2cd/0x5e0 net/socket.c:-1
___sys_recvmsg+0x21a/0x5c0 net/socket.c:2706
do_recvmmsg+0x382/0x850 net/socket.c:2800
__sys_recvmmsg net/socket.c:2879 [inline]
__do_sys_recvmmsg net/socket.c:2902 [inline]
__se_sys_recvmmsg net/socket.c:2895 [inline]
__x64_sys_recvmmsg+0x195/0x250 net/socket.c:2895
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: 0033:0x7f8bfb958819
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:00007f8bf9bb2028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007f8bfbbd1fa0 RCX: 00007f8bfb958819
RDX: 00000000080002c1 RSI: 0000200000000040 RDI: 0000000000000003
RBP: 00007f8bfb9eec91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8bfbbd2038 R14: 00007f8bfbbd1fa0 R15: 00007fffb22d5a88
----------------
Code disassembly (best guess):
0: c7 44 24 20 00 00 00 movl $0x0,0x20(%rsp)
7: 00
8: 9c pushf
9: 8f 44 24 20 pop 0x20(%rsp)
d: f7 44 24 20 00 02 00 testl $0x200,0x20(%rsp)
14: 00
15: 41 c6 04 07 f8 movb $0xf8,(%r15,%rax,1)
1a: 75 4b jne 0x67
1c: f7 c3 00 02 00 00 test $0x200,%ebx
22: 74 01 je 0x25
24: fb sti
25: bf 01 00 00 00 mov $0x1,%edi
* 2a: e8 2f 8a 8c f7 call 0xf78c8a5e <-- trapping instruction
2f: 65 8b 05 d0 97 3c 76 mov %gs:0x763c97d0(%rip),%eax # 0x763c9806
36: 85 c0 test %eax,%eax
38: 74 3c je 0x76
3a: 48 rex.W
3b: c7 .byte 0xc7
3c: 04 24 add $0x24,%al
3e: 0e (bad)
3f: 36 ss