=============================
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.1.442/5871:
 #0: ffff888016dee460
 (
sb_writers#3
){.+.+}-{0:0}
, at: vfs_write+0x296/0xd70 fs/read_write.c:590
 #1: ffff88807b72dfc0 (&sb->s_type->i_mutex_key#8){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:793 [inline]
 #1: ffff88807b72dfc0 (&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: ffff88802aa9c908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #3: ffff88802aa9c908 (&sch->q.lock){+.-.}-{2:2}, at: sfq_perturbation+0x14d/0x2090 net/sched/sch_sfq.c:610
 #4: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 5871 Comm: syz.1.442 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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:800
 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:bytes_is_nonzero mm/kasan/generic.c:85 [inline]
RIP: 0010:memory_is_nonzero mm/kasan/generic.c:102 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]
RIP: 0010:check_region_inline mm/kasan/generic.c:180 [inline]
RIP: 0010:kasan_check_range+0x84/0x290 mm/kasan/generic.c:189
Code: 49 c1 e9 03 4b 8d 1c 21 49 89 df 4d 29 df 49 83 ff 10 7f 29 4d 85 ff 0f 84 38 01 00 00 4c 89 cb 48 f7 d3 4c 01 f3 41 80 3b 00 <0f> 85 86 01 00 00 49 ff c3 48 ff c3 75 ee e9 18 01 00 00 44 89 dd
RSP: 0018:ffffc9000390f030 EFLAGS: 00000246
RAX: ffffffff81c49d01 RBX: fffffffffffffff5 RCX: ffffffff81c49daf
RDX: 0000000000000001 RSI: 0000000000000080 RDI: ffffc9000390f0c0
RBP: 0000000000000000 R08: ffffc9000390f13f R09: 1ffff92000721e27
R10: dffffc0000000000 R11: fffff52000721e1d R12: dffffc0000000001
R13: 0000000000000981 R14: 1ffff92000721e18 R15: 0000000000000010
 memset+0x1e/0x40 mm/kasan/shadow.c:44
 save_stack+0xaf/0x230 mm/page_owner.c:103
 __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:2179 [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: 0033:0x7f849756598e
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:00007f84957fcda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f84957fd6c0 RCX: 00007f849756598e
RDX: 0000000000200000 RSI: 00007f848d3dd000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007f84957fcee0 R14: 00007f84957fcea0 R15: 00007f848d3dd000
 </TASK>
----------------
Code disassembly (best guess):
   0:	49 c1 e9 03          	shr    $0x3,%r9
   4:	4b 8d 1c 21          	lea    (%r9,%r12,1),%rbx
   8:	49 89 df             	mov    %rbx,%r15
   b:	4d 29 df             	sub    %r11,%r15
   e:	49 83 ff 10          	cmp    $0x10,%r15
  12:	7f 29                	jg     0x3d
  14:	4d 85 ff             	test   %r15,%r15
  17:	0f 84 38 01 00 00    	je     0x155
  1d:	4c 89 cb             	mov    %r9,%rbx
  20:	48 f7 d3             	not    %rbx
  23:	4c 01 f3             	add    %r14,%rbx
  26:	41 80 3b 00          	cmpb   $0x0,(%r11)
* 2a:	0f 85 86 01 00 00    	jne    0x1b6 <-- trapping instruction
  30:	49 ff c3             	inc    %r11
  33:	48 ff c3             	inc    %rbx
  36:	75 ee                	jne    0x26
  38:	e9 18 01 00 00       	jmp    0x155
  3d:	44 89 dd             	mov    %r11d,%ebp