=============================
WARNING: suspicious RCU usage
5.15.185-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 ksoftirqd/0/14:
 #0: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311
 #1: ffff0000d6a04948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: qdisc_run+0x2c/0x1f8 include/net/pkt_sched.h:131
 #2: ffff0000d6a04908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #2: ffff0000d6a04908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x1e4/0x3bc net/sched/sch_generic.c:354
 #3: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:311

stack backtrace:
CPU: 0 PID: 14 Comm: ksoftirqd/0 Not tainted 5.15.185-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call trace:
 dump_backtrace+0x0/0x43c arch/arm64/kernel/stacktrace.c:152
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 lockdep_rcu_suspicious+0x140/0x198 kernel/locking/lockdep.c:6574
 qdisc_lookup+0xc8/0x64c net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x204/0x4a0 net/sched/sch_api.c:800
 cake_dequeue+0x1800/0x3afc net/sched/sch_cake.c:2189
 qdisc_peek_dequeued+0x78/0x1ec include/net/sch_generic.h:1115
 tbf_dequeue+0x90/0xc5c net/sched/sch_tbf.c:265
 dequeue_skb net/sched/sch_generic.c:292 [inline]
 qdisc_restart net/sched/sch_generic.c:397 [inline]
 __qdisc_run+0x1bc/0x1170 net/sched/sch_generic.c:415
 qdisc_run+0x40/0x1f8 include/net/pkt_sched.h:132
 net_tx_action+0x630/0x81c net/core/dev.c:5128
 handle_softirqs+0x344/0xbf0 kernel/softirq.c:576
 run_ksoftirqd+0x7c/0x2a0 kernel/softirq.c:943
 smpboot_thread_fn+0x4b0/0x920 kernel/smpboot.c:164
 kthread+0x374/0x454 kernel/kthread.c:334
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870
GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog