=============================
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
8 locks held by syz.4.2458/12296:
#0: ffffc90000dd0be0 ((&icsk->icsk_retransmit_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
#0: ffffc90000dd0be0 ((&icsk->icsk_retransmit_timer)){+.-.}-{0:0}, at: call_timer_fn+0xca/0x540 kernel/time/timer.c:1638
#1: ffff88807de498a0 (slock-AF_INET){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
#1: ffff88807de498a0 (slock-AF_INET){+.-.}-{2:2}, at: tcp_write_timer+0x29/0x280 net/ipv4/tcp_timer.c:673
#2: ffffffff8c31eb20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#3: ffffffff8c31eb20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#4: ffffffff8c31eb80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#5: ffffffff8c31eb80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
#6: ffff88802224d108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
#6: ffff88802224d108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3924 [inline]
#6: ffff88802224d108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xa2a/0x2f80 net/core/dev.c:4266
#7: ffffffff8c31eb20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
stack backtrace:
CPU: 1 PID: 12296 Comm: syz.4.2458 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
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
pfifo_tail_enqueue+0x372/0x4d0 net/sched/sch_fifo.c:54
qdisc_enqueue include/net/sch_generic.h:842 [inline]
tbf_enqueue+0x224/0x6e0 net/sched/sch_tbf.c:243
dev_qdisc_enqueue+0x48/0x210 net/core/dev.c:3865
__dev_xmit_skb net/core/dev.c:3949 [inline]
__dev_queue_xmit+0xc25/0x2f80 net/core/dev.c:4266
neigh_hh_output include/net/neighbour.h:493 [inline]
neigh_output include/net/neighbour.h:507 [inline]
ip_finish_output2+0xc87/0x10a0 net/ipv4/ip_output.c:228
NF_HOOK_COND include/linux/netfilter.h:291 [inline]
ip_output+0x2c0/0x3e0 net/ipv4/ip_output.c:434
dst_output include/net/dst.h:452 [inline]
ip_local_out net/ipv4/ip_output.c:126 [inline]
__ip_queue_xmit+0x11c1/0x1c00 net/ipv4/ip_output.c:538
__tcp_transmit_skb+0x1d11/0x3200 net/ipv4/tcp_output.c:1404
tcp_transmit_skb net/ipv4/tcp_output.c:1422 [inline]
__tcp_retransmit_skb+0x92c/0x1290 net/ipv4/tcp_output.c:3278
tcp_retransmit_skb+0x2e/0x350 net/ipv4/tcp_output.c:3301
tcp_retransmit_timer+0x144b/0x2540 net/ipv4/tcp_timer.c:570
tcp_write_timer_handler+0x205/0x9a0 net/ipv4/tcp_timer.c:655
tcp_write_timer+0x126/0x280 net/ipv4/tcp_timer.c:675
call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
expire_timers kernel/time/timer.c:1699 [inline]
__run_timers+0x53e/0x800 kernel/time/timer.c:1970
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
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
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:finish_lock_switch+0x134/0x280 kernel/sched/core.c:4804
Code: be ff ff ff ff e8 3c 62 68 08 85 c0 74 4a 4d 85 ff 75 66 e9 fe 00 00 00 48 89 df e8 e6 cd 71 08 e8 61 e6 2a 00 fb 48 83 c4 08 <5b> 41 5c 41 5d 41 5e 41 5f 5d c3 48 89 df e8 c9 09 fe ff 43 80 3c
RSP: 0018:ffffc9000326f2c8 EFLAGS: 00000282
RAX: 7fa666f843b65d00 RBX: ffff8880b903a340 RCX: 7fa666f843b65d00
RDX: dffffc0000000000 RSI: ffffffff8a2b2800 RDI: ffffffff8a79fe40
RBP: 1ffff11017227613 R08: ffff8880b903a343 R09: 1ffff11017207468
R10: dffffc0000000000 R11: ffffed1017207469 R12: ffff8880b913b088
R13: dffffc0000000000 R14: ffff8880b913ae08 R15: 0000000000000000
finish_task_switch+0x12f/0x640 kernel/sched/core.c:4921
context_switch kernel/sched/core.c:5052 [inline]
__schedule+0x11f7/0x43c0 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0xbd/0x2d0 kernel/time/timer.c:2093
unix_wait_for_peer+0x1f2/0x2e0 net/unix/af_unix.c:1315
unix_dgram_sendmsg+0x1083/0x18a0 net/unix/af_unix.c:1910
sock_sendmsg_nosec net/socket.c:706 [inline]
__sock_sendmsg net/socket.c:718 [inline]
____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445
___sys_sendmsg+0x236/0x2e0 net/socket.c:2499
__sys_sendmmsg+0x2ba/0x500 net/socket.c:2585
__do_sys_sendmmsg net/socket.c:2614 [inline]
__se_sys_sendmmsg net/socket.c:2611 [inline]
__x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2611
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: 0033:0x7f843f55bdd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f843d7b5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f843f7d4fa0 RCX: 00007f843f55bdd9
RDX: 0000000000000651 RSI: 0000200000000000 RDI: 0000000000000007
RBP: 00007f843f5f1d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f843f7d5038 R14: 00007f843f7d4fa0 R15: 00007ffcb0d0d3c8
vkms_vblank_simulate: vblank timer overrun
----------------
Code disassembly (best guess):
0: be ff ff ff ff mov $0xffffffff,%esi
5: e8 3c 62 68 08 call 0x8686246
a: 85 c0 test %eax,%eax
c: 74 4a je 0x58
e: 4d 85 ff test %r15,%r15
11: 75 66 jne 0x79
13: e9 fe 00 00 00 jmp 0x116
18: 48 89 df mov %rbx,%rdi
1b: e8 e6 cd 71 08 call 0x871ce06
20: e8 61 e6 2a 00 call 0x2ae686
25: fb sti
26: 48 83 c4 08 add $0x8,%rsp
* 2a: 5b pop %rbx <-- trapping instruction
2b: 41 5c pop %r12
2d: 41 5d pop %r13
2f: 41 5e pop %r14
31: 41 5f pop %r15
33: 5d pop %rbp
34: c3 ret
35: 48 89 df mov %rbx,%rdi
38: e8 c9 09 fe ff call 0xfffe0a06
3d: 43 rex.XB
3e: 80 .byte 0x80
3f: 3c .byte 0x3c