=============================
WARNING: suspicious RCU usage
5.15.173-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 udevd/3640:
 #0: ffff800014c922e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311
 #1: ffff0000e678b948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: qdisc_run+0x2c/0x200 include/net/pkt_sched.h:131
 #2: ffff0000e678b908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #2: ffff0000e678b908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x210/0x484 net/sched/sch_generic.c:354
 #3: ffff800014c922e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:311

stack backtrace:
CPU: 1 PID: 3640 Comm: udevd Not tainted 5.15.173-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
Call trace:
 dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 dump_stack+0x1c/0x58 lib/dump_stack.c:113
 lockdep_rcu_suspicious+0x188/0x1e0 kernel/locking/lockdep.c:6571
 qdisc_lookup+0xc8/0x64c net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x208/0x4a4 net/sched/sch_api.c:800
 cake_dequeue+0x18e0/0x3acc net/sched/sch_cake.c:2179
 qdisc_peek_dequeued+0x74/0x204 include/net/sch_generic.h:1100
 tbf_dequeue+0x90/0xd0c net/sched/sch_tbf.c:259
 dequeue_skb net/sched/sch_generic.c:292 [inline]
 qdisc_restart net/sched/sch_generic.c:397 [inline]
 __qdisc_run+0x1ec/0x1fc0 net/sched/sch_generic.c:415
 qdisc_run+0x40/0x200 include/net/pkt_sched.h:132
 net_tx_action+0x698/0x884 net/core/dev.c:5096
 handle_softirqs+0x384/0xdbc kernel/softirq.c:558
 __do_softirq kernel/softirq.c:592 [inline]
 do_softirq_own_stack include/asm-generic/softirq_stack.h:10 [inline]
 invoke_softirq kernel/softirq.c:439 [inline]
 __irq_exit_rcu+0x268/0x4d8 kernel/softirq.c:641
 irq_exit+0x14/0x88 kernel/softirq.c:665
 handle_domain_irq+0xf4/0x178 kernel/irq/irqdesc.c:711
 gic_handle_irq+0x78/0x1c8 drivers/irqchip/irq-gic-v3.c:765
 call_on_irq_stack+0x24/0x4c arch/arm64/kernel/entry.S:899
 do_interrupt_handler+0x74/0x94 arch/arm64/kernel/entry-common.c:267
 el1_interrupt+0x30/0x58 arch/arm64/kernel/entry-common.c:454
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:470
 el1h_64_irq+0x78/0x7c arch/arm64/kernel/entry.S:522
 local_daif_restore arch/arm64/include/asm/daifflags.h:117 [inline]
 do_notify_resume+0x194/0x32b8 arch/arm64/kernel/signal.c:931
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:133 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:138 [inline]
 el0_svc+0xfc/0x1f0 arch/arm64/kernel/entry-common.c:609
 el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
 el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584