=============================
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 syz.8.857/7770:
 #0: ffff800014c922e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311
 #1: ffff0000d37ee948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: qdisc_run+0x2c/0x200 include/net/pkt_sched.h:131
 #2: ffff0000d37ee908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #2: ffff0000d37ee908 (&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: 0 PID: 7770 Comm: syz.8.857 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
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:122 [inline]
 lock_release+0x504/0xa1c kernel/locking/lockdep.c:5646
 __mutex_unlock_slowpath+0xe0/0x6d4 kernel/locking/mutex.c:851
 mutex_unlock+0x8c/0xe0 kernel/locking/mutex.c:536
 rng_dev_read+0x278/0x608 drivers/char/hw_random/core.c:258
 do_iter_read+0x434/0x684 fs/read_write.c:792
 vfs_readv fs/read_write.c:910 [inline]
 do_preadv+0x1e4/0x324 fs/read_write.c:1002
 __do_sys_preadv fs/read_write.c:1052 [inline]
 __se_sys_preadv fs/read_write.c:1047 [inline]
 __arm64_sys_preadv+0xa0/0xb8 fs/read_write.c:1047
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
 el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
 el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
 el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584