=============================
WARNING: suspicious RCU usage
5.15.189-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
7 locks held by syz.2.121/4842:
#0: ffff88807dcfb928 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
#0: ffff88807dcfb928 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x15d/0x2b0 mm/util.c:549
#1: ffffc90000dd0be0 ((&d->timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
#1: ffffc90000dd0be0 ((&d->timer)){+.-.}-{0:0}, at: call_timer_fn+0xbb/0x530 kernel/time/timer.c:1441
#2: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
#3: ffffffff8c11c3c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
#4: ffff88807863a108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
#4: ffff88807863a108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline]
#4: ffff88807863a108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xb8a/0x2ed0 net/core/dev.c:4253
#5: ffff88807863a148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: tipc_l2_send_msg+0x30a/0x3c0 net/tipc/bearer.c:518
#6: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
stack backtrace:
CPU: 1 PID: 4842 Comm: syz.2.121 Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
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:793
fq_codel_enqueue+0x101a/0x1590 net/sched/sch_fq_codel.c:243
qdisc_enqueue include/net/sch_generic.h:832 [inline]
netem_dequeue+0xd39/0x1400 net/sched/sch_netem.c:737
dequeue_skb net/sched/sch_generic.c:292 [inline]
qdisc_restart net/sched/sch_generic.c:397 [inline]
__qdisc_run+0x237/0x1480 net/sched/sch_generic.c:415
__dev_xmit_skb net/core/dev.c:3942 [inline]
__dev_queue_xmit+0xeb9/0x2ed0 net/core/dev.c:4253
tipc_l2_send_msg+0x30a/0x3c0 net/tipc/bearer.c:518
tipc_bearer_xmit_skb+0x292/0x3c0 net/tipc/bearer.c:577
tipc_disc_timeout+0x568/0x6b0 net/tipc/discover.c:338
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
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
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
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:unwind_next_frame+0xa41/0x1d90 arch/x86/kernel/unwind_orc.c:549
Code: 68 42 0f b6 04 28 84 c0 4c 8b 74 24 28 0f 85 40 10 00 00 41 c6 07 00 ba 10 00 00 00 4c 89 f7 31 f6 e8 73 a6 87 00 48 8b 3c 24 ec 04 00 00 48 89 54 24 50 48 8d 7b 08 48 89 f8 48 c1 e8 03 42
RSP: 0018:ffffc900053975e8 EFLAGS: 00000202
RAX: ffffc900053976f8 RBX: ffffc900053976a8 RCX: 0000000000000000
RDX: 0000000000000010 RSI: 0000000000000000 RDI: ffffffff8de87230
RBP: ffffc900053976f0 R08: dffffc0000000000 R09: ffffc900053976f8
R10: fffff52000a72ee1 R11: 1ffff92000a72edf R12: 1ffffffff1bd0e46
R13: dffffc0000000000 R14: ffffc900053976f8 R15: ffffc900053976dd
arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x98/0xe0 kernel/stacktrace.c:122
save_stack+0xf3/0x1e0 mm/page_owner.c:119
__reset_page_owner+0x51/0x180 mm/page_owner.c:140
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1340 [inline]
free_pcp_prepare mm/page_alloc.c:1391 [inline]
free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
free_unref_page+0x94/0x280 mm/page_alloc.c:3396
__vunmap+0x8ab/0xa40 mm/vmalloc.c:2621
kcov_mmap+0x89/0x120 kernel/kcov.c:498
call_mmap include/linux/fs.h:2177 [inline]
mmap_file+0x5d/0xb0 mm/util.c:1092
__mmap_region mm/mmap.c:1792 [inline]
mmap_region+0xd0d/0x15e0 mm/mmap.c:2929
do_mmap+0x77a/0xdf0 mm/mmap.c:1582
vm_mmap_pgoff+0x1b2/0x2b0 mm/util.c:551
ksys_mmap_pgoff+0x542/0x780 mm/mmap.c:1631
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: 0033:0x7f425792bc23
Code: f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 41 89 ca 41 f7 c1 ff 0f 00 00 75 14 b8 09 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 25 c3 0f 1f 40 00 48 c7 c0 a8 ff ff ff 64 c7
RSP: 002b:00007ffe04c0cdc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f4257b53308 RCX: 00007f425792bc23
RDX: 0000000000000003 RSI: 0000000000400000 RDI: 00007f4255730000
RBP: 00007f4257b53270 R08: 00000000000000db R09: 0000000000000000
R10: 0000000000000011 R11: 0000000000000246 R12: 0000000000000003
R13: 00007f4257b53270 R14: 0000000000001c26 R15: 0000000000000003
----------------
Code disassembly (best guess):
0: 68 42 0f b6 04 push $0x4b60f42
5: 28 84 c0 4c 8b 74 24 sub %al,0x24748b4c(%rax,%rax,8)
c: 28 0f sub %cl,(%rdi)
e: 85 40 10 test %eax,0x10(%rax)
11: 00 00 add %al,(%rax)
13: 41 c6 07 00 movb $0x0,(%r15)
17: ba 10 00 00 00 mov $0x10,%edx
1c: 4c 89 f7 mov %r14,%rdi
1f: 31 f6 xor %esi,%esi
21: e8 73 a6 87 00 call 0x87a699
26: 48 8b 3c 24 mov (%rsp),%rdi
* 2a: e9 ec 04 00 00 jmp 0x51b <-- trapping instruction
2f: 48 89 54 24 50 mov %rdx,0x50(%rsp)
34: 48 8d 7b 08 lea 0x8(%rbx),%rdi
38: 48 89 f8 mov %rdi,%rax
3b: 48 c1 e8 03 shr $0x3,%rax
3f: 42 rex.X