=============================
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 udevd/4196:
 #0: ffffc90000007c00 ((&q->perturb_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
 #0: ffffc90000007c00 ((&q->perturb_timer)){+.-.}-{0:0}, at: call_timer_fn+0xbb/0x530 kernel/time/timer.c:1441
 #1: ffff88802221e908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #1: ffff88802221e908 (&sch->q.lock){+.-.}-{2:2}, at: sfq_perturbation+0x12e/0x2060 net/sched/sch_sfq.c:610
 #2: ffffffff8c11c720 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 4196 Comm: udevd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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:783
 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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: f6 ff 0f 1f 00 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 be 2b b1 f7 48 89 df e8 86 00 b2 f7 e8 21 9a d2 f7 fb bf 01 00 00 00 <e8> 56 22 a6 f7 65 8b 05 e7 1f 57 76 85 c0 74 02 5b c3 e8 f4 2a 55
RSP: 0018:ffffc90002f2f7f0 EFLAGS: 00000286
RAX: c8c7d0f9a3f47300 RBX: ffff888024de0fc8 RCX: c8c7d0f9a3f47300
RDX: dffffc0000000000 RSI: ffffffff8a0b1be0 RDI: 0000000000000001
RBP: dffffc0000000000 R08: dffffc0000000000 R09: ffffed10049bc1fa
R10: ffffed10049bc1fa R11: 1ffff110049bc1f9 R12: 00fff00000080017
R13: 0000000000000000 R14: ffff888024de0fc0 R15: ffff888024de0fc8
 spin_unlock_irq include/linux/spinlock.h:414 [inline]
 delete_from_page_cache+0x129/0x190 mm/filemap.c:267
 truncate_inode_page+0x8d/0xb0 mm/truncate.c:219
 shmem_undo_range+0x4dc/0x1880 mm/shmem.c:960
 shmem_truncate_range mm/shmem.c:1063 [inline]
 shmem_evict_inode+0x20d/0xa00 mm/shmem.c:1145
 evict+0x485/0x870 fs/inode.c:647
 __dentry_kill+0x431/0x650 fs/dcache.c:586
 dentry_kill+0xb8/0x290 fs/dcache.c:-1
 dput+0xd8/0x1a0 fs/dcache.c:893
 __fput+0x5ee/0x930 fs/file_table.c:319
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f616271c407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007fff5cf90750 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 00007f616262e880 RCX: 00007f616271c407
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008
RBP: 00007f616262e6e8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
R13: 000056330c5aa410 R14: 0000000000000008 R15: 000056330c5b8820
 </TASK>
----------------
Code disassembly (best guess):
   0:	f6 ff                	idiv   %bh
   2:	0f 1f 00             	nopl   (%rax)
   5:	53                   	push   %rbx
   6:	48 89 fb             	mov    %rdi,%rbx
   9:	48 83 c7 18          	add    $0x18,%rdi
   d:	48 8b 74 24 08       	mov    0x8(%rsp),%rsi
  12:	e8 be 2b b1 f7       	call   0xf7b12bd5
  17:	48 89 df             	mov    %rbx,%rdi
  1a:	e8 86 00 b2 f7       	call   0xf7b200a5
  1f:	e8 21 9a d2 f7       	call   0xf7d29a45
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 56 22 a6 f7       	call   0xf7a62285 <-- trapping instruction
  2f:	65 8b 05 e7 1f 57 76 	mov    %gs:0x76571fe7(%rip),%eax        # 0x7657201d
  36:	85 c0                	test   %eax,%eax
  38:	74 02                	je     0x3c
  3a:	5b                   	pop    %rbx
  3b:	c3                   	ret
  3c:	e8                   	.byte 0xe8
  3d:	f4                   	hlt
  3e:	2a                   	.byte 0x2a
  3f:	55                   	push   %rbp