=============================
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
9 locks held by kworker/u4:2/154:
#0: ffff8880169cd938 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
#1: ffffc90001e57d00 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
#2: ffffffff8d226b10 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x132/0xb80 net/core/net_namespace.c:589
#3: ffffffff8c11c720 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
#4: ffffc90000007be0 ((&d->timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
#4: ffffc90000007be0 ((&d->timer)){+.-.}-{0:0}, at: call_timer_fn+0xbb/0x530 kernel/time/timer.c:1441
#5: ffffffff8c11c720 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
#6: ffffffff8c11c780 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#7: ffff8880181bc108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
#7: ffff8880181bc108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline]
#7: ffff8880181bc108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xb8a/0x2ed0 net/core/dev.c:4253
#8: ffffffff8c11c720 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
stack backtrace:
CPU: 0 PID: 154 Comm: kworker/u4:2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: netns cleanup_net
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:783
cake_drop net/sched/sch_cake.c:1611 [inline]
cake_enqueue+0x3889/0x7bb0 net/sched/sch_cake.c:1948
cbs_child_enqueue net/sched/sch_cbs.c:95 [inline]
cbs_enqueue_soft+0x1a8/0x270 net/sched/sch_cbs.c:128
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:lock_acquire+0x1f2/0x3f0 kernel/locking/lockdep.c:5627
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f6 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 66 43 c7 44 3d 09 00 00 43 c6 44 3d 0b
RSP: 0018:ffffc90001e57900 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: f468935a00e58d00
RDX: 0000000000000000 RSI: ffffffff8a0b2e80 RDI: ffffffff8a59e800
RBP: ffffc90001e57a20 R08: dffffc0000000000 R09: fffffbfff1ff5419
R10: fffffbfff1ff5419 R11: 1ffffffff1ff5418 R12: ffffffff8c11c720
R13: 1ffff920003caf2c R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:313
rcu_read_lock include/linux/rcupdate.h:740 [inline]
inet_twsk_purge+0x119/0x810 net/ipv4/inet_timewait_sock.c:268
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x77b/0xb80 net/core/net_namespace.c:635
process_one_work+0x863/0x1000 kernel/workqueue.c:2310
worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
----------------
Code disassembly (best guess):
0: 00 9c 8f 84 24 80 00 add %bl,0x802484(%rdi,%rcx,4)
7: 00 00 add %al,(%rax)
9: f6 84 24 81 00 00 00 testb $0x2,0x81(%rsp)
10: 02
11: 0f 85 f6 00 00 00 jne 0x10d
17: 41 f7 c6 00 02 00 00 test $0x200,%r14d
1e: 74 01 je 0x21
20: fb sti
21: 48 c7 44 24 60 0e 36 movq $0x45e0360e,0x60(%rsp)
28: e0 45
* 2a: 4b c7 44 3d 00 00 00 movq $0x0,0x0(%r13,%r15,1) <-- trapping instruction
31: 00 00
33: 66 43 c7 44 3d 09 00 movw $0x0,0x9(%r13,%r15,1)
3a: 00
3b: 43 rex.XB
3c: c6 .byte 0xc6
3d: 44 rex.R
3e: 3d .byte 0x3d
3f: 0b .byte 0xb