=============================
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
3 locks held by syz.4.151/4903:
 #0: ffffc90000007cc0 ((&q->perturb_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
 #0: ffffc90000007cc0 ((&q->perturb_timer)){+.-.}-{0:0}, at: call_timer_fn+0xca/0x540 kernel/time/timer.c:1638
 #1: ffff88805fa79108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #1: ffff88805fa79108 (&sch->q.lock){+.-.}-{2:2}, at: sfq_perturbation+0x14d/0x20d0 net/sched/sch_sfq.c:610
 #2: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 4903 Comm: syz.4.151 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 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
 sfq_rehash net/sched/sch_sfq.c:598 [inline]
 sfq_perturbation+0x1f5e/0x20d0 net/sched/sch_sfq.c:613
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x53e/0x800 kernel/time/timer.c:1970
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 do_softirq+0x142/0x210 kernel/softirq.c:477
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x180/0x1c0 kernel/softirq.c:401
 spin_unlock_bh include/linux/spinlock.h:409 [inline]
 packet_poll+0x346/0x5f0 net/packet/af_packet.c:4289
 sock_poll+0x34f/0x410 net/socket.c:1333
 vfs_poll include/linux/poll.h:94 [inline]
 do_select+0x100d/0x1790 fs/select.c:537
 core_sys_select+0x6fe/0x930 fs/select.c:680
 do_pselect fs/select.c:762 [inline]
 __do_sys_pselect6 fs/select.c:803 [inline]
 __se_sys_pselect6+0x2f4/0x3c0 fs/select.c:794
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f2859a8b819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f2857cc4028 EFLAGS: 00000246 ORIG_RAX: 000000000000010e
RAX: ffffffffffffffda RBX: 00007f2859d05090 RCX: 00007f2859a8b819
RDX: 0000000000000000 RSI: 0000200000000240 RDI: 0000000000000040
RBP: 00007f2859b21c91 R08: 0000000000000000 R09: 0000000000000000
R10: 00002000000002c0 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2859d05128 R14: 00007f2859d05090 R15: 00007fff3400bdb8
 </TASK>