=============================
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
10 locks held by kworker/0:0/7:
 #0: ffff88802acd3138 ((wq_completion)mld){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc90000cc7d00 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
 #2: ffff888021e58530 (&idev->mc_lock){+.+.}-{3:3}, at: mld_ifc_work+0x29/0xb40 net/ipv6/mcast.c:2657
 #3: ffffffff8c11c460 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
 #4: ffffffff8c11c4c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #5: ffffffff8c11c4c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #6: ffffffff8c11c4c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #7: ffffffff8c11c4c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #8: ffff8880609cf108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #8: ffff8880609cf108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline]
 #8: ffff8880609cf108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xb8a/0x2ed0 net/core/dev.c:4253
 #9: ffffffff8c11c460 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311

stack backtrace:
CPU: 0 PID: 7 Comm: kworker/0:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: mld mld_ifc_work
Call Trace:
 <TASK>
 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:793
 sfq_enqueue+0x148e/0x2260 net/sched/sch_sfq.c:-1
 qdisc_enqueue include/net/sch_generic.h:832 [inline]
 tbf_enqueue+0x224/0x6e0 net/sched/sch_tbf.c:243
 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
 neigh_hh_output include/net/neighbour.h:493 [inline]
 neigh_output include/net/neighbour.h:507 [inline]
 ip_finish_output2+0xc69/0x1080 net/ipv4/ip_output.c:228
 iptunnel_xmit+0x525/0x960 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x1b6f/0x2240 net/ipv4/ip_tunnel.c:838
 __gre_xmit net/ipv4/ip_gre.c:474 [inline]
 ipgre_xmit+0x779/0xb00 net/ipv4/ip_gre.c:669
 __netdev_start_xmit include/linux/netdevice.h:5027 [inline]
 netdev_start_xmit include/linux/netdevice.h:5041 [inline]
 xmit_one net/core/dev.c:3649 [inline]
 dev_hard_start_xmit+0x2a5/0x7e0 net/core/dev.c:3665
 __dev_queue_xmit+0x19df/0x2ed0 net/core/dev.c:4288
 neigh_output include/net/neighbour.h:509 [inline]
 ip6_finish_output2+0x1070/0x1500 net/ipv6/ip6_output.c:130
 dst_output include/net/dst.h:452 [inline]
 NF_HOOK+0x15f/0x430 include/linux/netfilter.h:302
 mld_sendpack+0x713/0xc30 net/ipv6/mcast.c:1825
 mld_send_cr net/ipv6/mcast.c:2126 [inline]
 mld_ifc_work+0x836/0xb40 net/ipv6/mcast.c:2658
 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
 </TASK>