=============================
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.9.935/8737:
 #0: ffff888016dee460 (sb_writers#3){.+.+}-{0:0}, at: vfs_write+0x296/0xd70 fs/read_write.c:590
 #1: ffff8880674aa190 (&sb->s_type->i_mutex_key#8){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:787 [inline]
 #1: ffff8880674aa190 (&sb->s_type->i_mutex_key#8){+.+.}-{3:3}, at: generic_file_write_iter+0x7e/0x1b0 mm/filemap.c:3941
 #2: ffffc90000007be0 ((&q->perturb_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
 #2: ffffc90000007be0 ((&q->perturb_timer)){+.-.}-{0:0}, at: call_timer_fn+0xca/0x540 kernel/time/timer.c:1638
 #3: ffff888078bc1908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #3: ffff888078bc1908 (&sch->q.lock){+.-.}-{2:2}, at: sfq_perturbation+0x14d/0x2090 net/sched/sch_sfq.c:610
 #4: ffffffff8c31ef20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 8737 Comm: syz.9.935 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 qdisc_lookup+0xa6/0x640 net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x188/0x480 net/sched/sch_api.c:783
 sfq_rehash net/sched/sch_sfq.c:598 [inline]
 sfq_perturbation+0x1f26/0x2090 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+0x56c/0x810 kernel/time/timer.c:1970
 handle_softirqs+0x336/0x830 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:__orc_find arch/x86/kernel/unwind_orc.c:52 [inline]
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:178 [inline]
RIP: 0010:unwind_next_frame+0xfe5/0x1cf0 arch/x86/kernel/unwind_orc.c:448
Code: b9 00 00 00 00 00 fc ff df 0f b6 04 08 84 c0 75 27 49 63 07 4c 01 f8 49 8d 4f 04 4c 39 f0 48 0f 46 e9 49 8d 47 fc 4c 0f 47 e8 <4d> 0f 46 e7 4c 39 ed 76 a8 e9 41 f2 ff ff 44 89 f9 80 e1 07 80 c1
RSP: 0018:ffffc90003d96eb0 EFLAGS: 00000293
RAX: ffffffff8d9eb304 RBX: ffffc90003d96f48 RCX: ffffffff8d9eb30c
RDX: ffffffff8e0d052a RSI: ffffffff8d9eb308 RDI: ffffffff81350ed7
RBP: ffffffff8d9eb30c R08: 0000000000000001 R09: 0000000000000006
R10: dffffc0000000000 R11: fffff520007b2df5 R12: ffffffff8d9eb308
R13: ffffffff8d9eb308 R14: ffffffff819f4895 R15: ffffffff8d9eb308
 arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 save_stack+0x121/0x230 mm/page_owner.c:119
 __set_page_owner+0x41/0x2d0 mm/page_owner.c:181
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_pages_vma+0x2bc/0x790 mm/mempolicy.c:2146
 shmem_alloc_page mm/shmem.c:1586 [inline]
 shmem_alloc_and_acct_page+0x47f/0xbe0 mm/shmem.c:1611
 shmem_getpage_gfp+0x14be/0x2c10 mm/shmem.c:1906
 shmem_getpage mm/shmem.c:151 [inline]
 shmem_write_begin+0xcd/0x1a0 mm/shmem.c:2474
 generic_perform_write+0x2b6/0x550 mm/filemap.c:3785
 __generic_file_write_iter+0x261/0x4e0 mm/filemap.c:3912
 generic_file_write_iter+0xa6/0x1b0 mm/filemap.c:3944
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 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: 0033:0x7fed0317768e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007fed0140eda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fed0140f6c0 RCX: 00007fed0317768e
RDX: 00000000013bd7ef RSI: 00007fecf8fef000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fed0140eee0 R14: 00007fed0140eea0 R15: 00007fecf8fef000
 </TASK>
----------------
Code disassembly (best guess):
   0:	b9 00 00 00 00       	mov    $0x0,%ecx
   5:	00 fc                	add    %bh,%ah
   7:	ff                   	lcall  (bad)
   8:	df 0f                	fisttps (%rdi)
   a:	b6 04                	mov    $0x4,%dh
   c:	08 84 c0 75 27 49 63 	or     %al,0x63492775(%rax,%rax,8)
  13:	07                   	(bad)
  14:	4c 01 f8             	add    %r15,%rax
  17:	49 8d 4f 04          	lea    0x4(%r15),%rcx
  1b:	4c 39 f0             	cmp    %r14,%rax
  1e:	48 0f 46 e9          	cmovbe %rcx,%rbp
  22:	49 8d 47 fc          	lea    -0x4(%r15),%rax
  26:	4c 0f 47 e8          	cmova  %rax,%r13
* 2a:	4d 0f 46 e7          	cmovbe %r15,%r12 <-- trapping instruction
  2e:	4c 39 ed             	cmp    %r13,%rbp
  31:	76 a8                	jbe    0xffffffdb
  33:	e9 41 f2 ff ff       	jmp    0xfffff279
  38:	44 89 f9             	mov    %r15d,%ecx
  3b:	80 e1 07             	and    $0x7,%cl
  3e:	80                   	.byte 0x80
  3f:	c1                   	.byte 0xc1