=============================
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
6 locks held by rm/8910:
 #0: ffff88807d938f28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff88807d938f28 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x16c/0x2d0 mm/util.c:549
 #1: ffffffff8c3f3448 (remove_cache_srcu){....}-{0:0}, at: rcu_lock_acquire+0x0/0x30
 #2: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #3: ffff8880766d3948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 #4: ffff8880766d3908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #4: ffff8880766d3908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
 #5: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 1 PID: 8910 Comm: rm Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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
 fq_codel_dequeue+0x26c5/0x28d0 net/sched/sch_fq_codel.c:319
 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:cmpxchg_double_slab+0x23/0x270 mm/slub.c:501
Code: 00 00 0f 1f 44 00 00 55 41 57 41 56 41 55 41 54 53 48 83 ec 10 4c 89 c3 49 89 cf 49 89 d4 49 89 f6 65 48 8b 04 25 28 00 00 00 <48> 89 44 24 08 f6 47 0b 40 0f 85 d5 00 00 00 4c 89 cd 48 c7 04 24
RSP: 0018:ffffc900042b76e0 EFLAGS: 00000282
RAX: 854a75d6f2c56700 RBX: ffff88807d9e8480 RCX: 00000000802a0021
RDX: ffff88807d9e8180 RSI: ffffea0001f67a00 RDI: ffff888016c4f780
RBP: 0000000000000000 R08: ffff88807d9e8480 R09: 00000000802a0020
R10: dffffc0000000000 R11: fffffbfff1b13c6e R12: ffff88807d9e8180
R13: 00000000802a0020 R14: ffffea0001f67a00 R15: 00000000802a0021
 __slab_free+0x6a/0x250 mm/slub.c:3355
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xd0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x100/0x290 mm/slub.c:3238
 vm_area_dup+0x1e/0xb0 kernel/fork.c:358
 __split_vma+0xb1/0x410 mm/mmap.c:2730
 __do_munmap+0x383/0xdf0 mm/mmap.c:2856
 do_munmap mm/mmap.c:2910 [inline]
 munmap_vma_range mm/mmap.c:603 [inline]
 __mmap_region mm/mmap.c:1757 [inline]
 mmap_region+0x8b4/0x1650 mm/mmap.c:2933
 do_mmap+0x819/0xe90 mm/mmap.c:1586
 vm_mmap_pgoff+0x1c1/0x2d0 mm/util.c:551
 ksys_mmap_pgoff+0x54b/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: 0033:0x7f2b6f88f242
Code: 08 00 04 00 00 eb e2 90 41 f7 c1 ff 0f 00 00 75 27 55 89 cd 53 48 89 fb 48 85 ff 74 33 41 89 ea 48 89 df b8 09 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 5e 5b 5d c3 0f 1f 00 c7 05 46 40 01 00 16 00
RSP: 002b:00007ffd61c14b88 EFLAGS: 00000206 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f2b6f5ad000 RCX: 00007f2b6f88f242
RDX: 0000000000000003 RSI: 0000000000002000 RDI: 00007f2b6f5ad000
RBP: 0000000000000812 R08: 0000000000000003 R09: 000000000000d000
R10: 0000000000000812 R11: 0000000000000206 R12: 00007ffd61c14c48
R13: 00007f2b6f86c580 R14: 00007ffd61c15000 R15: 00000fffac382974
 </TASK>
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
   7:	55                   	push   %rbp
   8:	41 57                	push   %r15
   a:	41 56                	push   %r14
   c:	41 55                	push   %r13
   e:	41 54                	push   %r12
  10:	53                   	push   %rbx
  11:	48 83 ec 10          	sub    $0x10,%rsp
  15:	4c 89 c3             	mov    %r8,%rbx
  18:	49 89 cf             	mov    %rcx,%r15
  1b:	49 89 d4             	mov    %rdx,%r12
  1e:	49 89 f6             	mov    %rsi,%r14
  21:	65 48 8b 04 25 28 00 	mov    %gs:0x28,%rax
  28:	00 00
* 2a:	48 89 44 24 08       	mov    %rax,0x8(%rsp) <-- trapping instruction
  2f:	f6 47 0b 40          	testb  $0x40,0xb(%rdi)
  33:	0f 85 d5 00 00 00    	jne    0x10e
  39:	4c 89 cd             	mov    %r9,%rbp
  3c:	48                   	rex.W
  3d:	c7                   	.byte 0xc7
  3e:	04 24                	add    $0x24,%al