=============================
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
4 locks held by syz.2.117/4908:
 #0: ffff88807b532b28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
 #0: ffff88807b532b28 (&mm->mmap_lock){++++}-{3:3}, at: do_user_addr_fault+0x2b9/0xc80 arch/x86/mm/fault.c:1298
 #1: ffffc90000007c00 ((&q->perturb_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
 #1: ffffc90000007c00 ((&q->perturb_timer)){+.-.}-{0:0}, at: call_timer_fn+0xbb/0x530 kernel/time/timer.c:1441
 #2: ffff88802a2e1908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #2: ffff88802a2e1908 (&sch->q.lock){+.-.}-{2:2}, at: sfq_perturbation+0x12e/0x2060 net/sched/sch_sfq.c:610
 #3: ffffffff8c11c760 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 4908 Comm: syz.2.117 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <IRQ>
 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_rehash net/sched/sch_sfq.c:598 [inline]
 sfq_perturbation+0x1f20/0x2060 net/sched/sch_sfq.c:613
 call_timer_fn+0x16c/0x530 kernel/time/timer.c:1451
 expire_timers kernel/time/timer.c:1496 [inline]
 __run_timers+0x525/0x7c0 kernel/time/timer.c:1767
 handle_softirqs+0x328/0x820 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x12f/0x220 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:check_kcov_mode kernel/kcov.c:183 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:227 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x32/0x80 kernel/kcov.c:293
Code: 44 a0 8a 7e 65 8b 15 45 a0 8a 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 5b 83 b9 34 16 00 00 00 74 52 8b 91 10 16 00 00 <83> fa 03 75 47 48 8b 91 18 16 00 00 44 8b 89 14 16 00 00 49 c1 e1
RSP: 0000:ffffc9000348fe78 EFLAGS: 00000246
RAX: ffffffff8134e3ca RBX: 0000000000000000 RCX: ffff8880215d5940
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: dffffc0000000000 R09: ffffed10045fa6f1
R10: ffffed10045fa6f1 R11: 1ffff110045fa6f0 R12: ffffc9000348ff58
R13: 0000000000000255 R14: 0000000000000006 R15: 00007fb27eef1000
 fault_signal_pending include/linux/sched/signal.h:408 [inline]
 do_user_addr_fault+0x49a/0xc80 arch/x86/mm/fault.c:1359
 handle_page_fault arch/x86/mm/fault.c:1445 [inline]
 exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1501
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606
RIP: 0033:0x7fb288e38cb0
Code: 39 4f 08 72 4c 8d 4d ff 85 ed 74 33 66 0f 1f 44 00 00 48 39 f0 72 1b 4d 8b 07 49 89 c1 49 29 f1 47 0f b6 0c 08 45 84 c9 74 08 <45> 88 0c 00 49 8b 47 10 48 83 c0 01 49 89 47 10 83 e9 01 73 d3 41
RSP: 002b:00007fb2871dd4a0 EFLAGS: 00010286
RAX: 0000000000133000 RBX: 00007fb2871dd540 RCX: 000000000000003f
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00007fb2871dd5e0
RBP: 0000000000000102 R08: 00007fb27edbe000 R09: 00000000000000ff
R10: 0000000000000000 R11: 00007fb2871dd550 R12: 0000000000000001
R13: 00007fb289015c40 R14: 0000000000000000 R15: 00007fb2871dd5e0
 </TASK>
----------------
Code disassembly (best guess):
   0:	44 a0 8a 7e 65 8b 15 	rex.R movabs 0x8aa045158b657e8a,%al
   7:	45 a0 8a
   a:	7e 81                	jle    0xffffff8d
   c:	e2 00                	loop   0xe
   e:	01 ff                	add    %edi,%edi
  10:	00 74 11 81          	add    %dh,-0x7f(%rcx,%rdx,1)
  14:	fa                   	cli
  15:	00 01                	add    %al,(%rcx)
  17:	00 00                	add    %al,(%rax)
  19:	75 5b                	jne    0x76
  1b:	83 b9 34 16 00 00 00 	cmpl   $0x0,0x1634(%rcx)
  22:	74 52                	je     0x76
  24:	8b 91 10 16 00 00    	mov    0x1610(%rcx),%edx
* 2a:	83 fa 03             	cmp    $0x3,%edx <-- trapping instruction
  2d:	75 47                	jne    0x76
  2f:	48 8b 91 18 16 00 00 	mov    0x1618(%rcx),%rdx
  36:	44 8b 89 14 16 00 00 	mov    0x1614(%rcx),%r9d
  3d:	49                   	rex.WB
  3e:	c1                   	.byte 0xc1
  3f:	e1                   	.byte 0xe1