=============================
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
5 locks held by syz.2.58/4478:
 #0: ffff88807a230f28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock include/linux/mmap_lock.h:117 [inline]
 #0: ffff88807a230f28 (&mm->mmap_lock){++++}-{3:3}, at: __mm_populate+0x164/0x3b0 mm/gup.c:1618
 #1: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #2: ffff88807bf30948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 #3: ffff88807bf30908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #3: ffff88807bf30908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
 #4: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 1 PID: 4478 Comm: syz.2.58 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
 cake_dequeue+0x1bd6/0x4b10 net/sched/sch_cake.c:2205
 qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1115
 tbf_dequeue+0x7d/0xce0 net/sched/sch_tbf.c:265
 dequeue_skb net/sched/sch_generic.c:295 [inline]
 qdisc_restart net/sched/sch_generic.c:400 [inline]
 __qdisc_run+0x236/0x1490 net/sched/sch_generic.c:418
 qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:131
 net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 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_region_inline mm/kasan/generic.c:169 [inline]
RIP: 0010:kasan_check_range+0xe/0x290 mm/kasan/generic.c:189
Code: 0f 0b b8 ea ff ff ff c3 0f 0b b8 ea ff ff ff c3 00 00 cc cc 00 00 cc cc 00 00 cc cc b0 01 48 85 f6 0f 84 ac 01 00 00 55 41 57 <41> 56 41 54 53 49 89 f8 49 01 f0 0f 82 0e 02 00 00 49 89 f8 49 c1
RSP: 0018:ffffc9000450f468 EFLAGS: 00000202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff815d0086
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff8d89e368
RBP: ffffc9000450f590 R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff940002c98e7 R12: ffff8880b9135578
R13: 1ffff920008a1e9c R14: 0000000000000001 R15: dffffc0000000000
 instrument_atomic_read include/linux/instrumented.h:71 [inline]
 test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
 cpumask_test_cpu include/linux/cpumask.h:344 [inline]
 cpu_online include/linux/cpumask.h:895 [inline]
 trace_lock_acquire include/trace/events/lock.h:13 [inline]
 lock_acquire+0xb6/0x400 kernel/locking/lockdep.c:5594
 local_lock_acquire+0x34/0x170 include/linux/local_lock_internal.h:29
 lru_cache_add+0x3bc/0x750 mm/swap.c:450
 shmem_getpage_gfp+0x186b/0x2d40 mm/shmem.c:1945
 shmem_fault+0x1ac/0x540 mm/shmem.c:2118
 __do_fault+0x141/0x330 mm/memory.c:3928
 do_read_fault mm/memory.c:4264 [inline]
 do_fault mm/memory.c:4392 [inline]
 handle_pte_fault mm/memory.c:4650 [inline]
 __handle_mm_fault mm/memory.c:4785 [inline]
 handle_mm_fault+0x2985/0x4410 mm/memory.c:4883
 faultin_page mm/gup.c:976 [inline]
 __get_user_pages+0x94b/0x11e0 mm/gup.c:1197
 populate_vma_page_range+0x213/0x290 mm/gup.c:1529
 __mm_populate+0x275/0x3b0 mm/gup.c:1638
 mm_populate include/linux/mm.h:2646 [inline]
 vm_mmap_pgoff+0x212/0x2d0 mm/util.c:556
 ksys_mmap_pgoff+0x140/0x790 mm/mmap.c:1635
 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: 0033:0x7fce53c9f819
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:00007fce51ef9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007fce53f18fa0 RCX: 00007fce53c9f819
RDX: b635773f06ebbeea RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007fce53d35c91 R08: ffffffffffffffff R09: 0000000028f43000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fce53f19038 R14: 00007fce53f18fa0 R15: 00007ffff74df098
 </TASK>
----------------
Code disassembly (best guess):
   0:	0f 0b                	ud2
   2:	b8 ea ff ff ff       	mov    $0xffffffea,%eax
   7:	c3                   	ret
   8:	0f 0b                	ud2
   a:	b8 ea ff ff ff       	mov    $0xffffffea,%eax
   f:	c3                   	ret
  10:	00 00                	add    %al,(%rax)
  12:	cc                   	int3
  13:	cc                   	int3
  14:	00 00                	add    %al,(%rax)
  16:	cc                   	int3
  17:	cc                   	int3
  18:	00 00                	add    %al,(%rax)
  1a:	cc                   	int3
  1b:	cc                   	int3
  1c:	b0 01                	mov    $0x1,%al
  1e:	48 85 f6             	test   %rsi,%rsi
  21:	0f 84 ac 01 00 00    	je     0x1d3
  27:	55                   	push   %rbp
  28:	41 57                	push   %r15
* 2a:	41 56                	push   %r14 <-- trapping instruction
  2c:	41 54                	push   %r12
  2e:	53                   	push   %rbx
  2f:	49 89 f8             	mov    %rdi,%r8
  32:	49 01 f0             	add    %rsi,%r8
  35:	0f 82 0e 02 00 00    	jb     0x249
  3b:	49 89 f8             	mov    %rdi,%r8
  3e:	49                   	rex.WB
  3f:	c1                   	.byte 0xc1