------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#1: pr/ttyS0/16
Modules linked in:
CPU: 1 UID: 0 PID: 16 Comm: pr/ttyS0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 db 60 e9 fc 48 8d 3d 14 d4 a6 0b 67 48 0f b9 3a eb 4a e8 c8 60 e9 fc 48 8d 3d 11 d4 a6 0b <67> 48 0f b9 3a eb 37 e8 b5 60 e9 fc 48 8d 3d 0e d4 a6 0b 67 48 0f
RSP: 0018:ffffc90000a18c28 EFLAGS: 00010246
RAX: ffffffff84de6488 RBX: 0000000000000002 RCX: ffff88801e298000
RDX: 0000000000000100 RSI: 0000000000000100 RDI: ffffffff908538a0
RBP: 0000000000000000 R08: ffff88801e298000 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000100 R12: dffffc0000000000
R13: 0000000000000001 R14: ffff8880212aa004 R15: ffff8880212aa3c0
FS:  0000000000000000(0000) GS:ffff888124dd6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2766158060 CR3: 0000000073c5a000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 sctp_generate_timeout_event+0x1c8/0x390 net/sctp/sm_sideeffect.c:284
 call_timer_fn+0x18d/0x5f0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2374 [inline]
 __run_timer_base+0x652/0x8b0 kernel/time/timer.c:2386
 run_timer_base kernel/time/timer.c:2395 [inline]
 run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2405
 handle_softirqs+0x226/0x860 kernel/softirq.c:645
 __do_softirq kernel/softirq.c:679 [inline]
 invoke_softirq kernel/softirq.c:519 [inline]
 __irq_exit_rcu+0xcb/0x220 kernel/softirq.c:758
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:775
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:211 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x47/0x80 kernel/locking/spinlock.c:221
Code: f7 e8 0d 6f bc f5 f7 c3 00 02 00 00 74 05 e8 f0 b1 e8 f5 9c 58 a9 00 02 00 00 75 29 f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 14 7e ad f5 65 48 8b 05 0c 41 ad 07 48 85 c0 74 18 5b 41 5e e9
RSP: 0018:ffffc90000157ca8 EFLAGS: 00000206
RAX: 0000000000000002 RBX: 0000000000000206 RCX: 8000000000000001
RDX: 0000000000000000 RSI: ffffffff8e474d50 RDI: 0000000000000001
RBP: ffffc90000157e18 R08: ffffffff907a1e7f R09: 1ffffffff20f43cf
R10: dffffc0000000000 R11: fffffbfff20f43d0 R12: 0000000000000002
R13: ffff88801e298000 R14: ffffffff9ad35080 R15: dffffc0000000000
 nbcon_emit_one kernel/printk/nbcon.c:1165 [inline]
 nbcon_kthread_func+0x6c4/0x880 kernel/printk/nbcon.c:1271
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	eb 66                	jmp    0x68
   2:	85 db                	test   %ebx,%ebx
   4:	74 3e                	je     0x44
   6:	83 fb 01             	cmp    $0x1,%ebx
   9:	75 4c                	jne    0x57
   b:	e8 db 60 e9 fc       	call   0xfce960eb
  10:	48 8d 3d 14 d4 a6 0b 	lea    0xba6d414(%rip),%rdi        # 0xba6d42b
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 c8 60 e9 fc       	call   0xfce960eb
  23:	48 8d 3d 11 d4 a6 0b 	lea    0xba6d411(%rip),%rdi        # 0xba6d43b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 b5 60 e9 fc       	call   0xfce960eb
  36:	48 8d 3d 0e d4 a6 0b 	lea    0xba6d40e(%rip),%rdi        # 0xba6d44b
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf