syzbot

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refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: ktimers/0/16
Modules linked in:
CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: 64 e3 f1 0a 67 48 0f b9 3a eb 4a e8 f8 2b 23 fd 48 8d 3d 61 e3 f1 0a 67 48 0f b9 3a eb 37 e8 e5 2b 23 fd 48 8d 3d 5e e3 f1 0a <67> 48 0f b9 3a eb 24 e8 d2 2b 23 fd 48 8d 3d 5b e3 f1 0a 67 48 0f
RSP: 0018:ffffc90000157a28 EFLAGS: 00010246
RAX: ffffffff84a13cdb RBX: 0000000000000003 RCX: ffff88801cee0000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffffffff8f932040
RBP: ffffc90000157b30 R08: ffff88801cee0000 R09: 0000000000000005
R10: 0000000000000100 R11: 0000000000000004 R12: 0000000000000000
R13: 00000000ffffd579 R14: ffff88805efae820 R15: ffff88805efae9b8
FS:  0000000000000000(0000) GS:ffff88812617d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000404030 CR3: 0000000040e8c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 call_timer_fn+0x192/0x5e0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2374 [inline]
 __run_timer_base+0x6a3/0x9f0 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+0x1de/0x6d0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 run_ktimerd+0x69/0x100 kernel/softirq.c:1151
 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
 kthread+0x388/0x470 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:	64 e3 f1             	fs jrcxz 0xfffffff4
   3:	0a 67 48             	or     0x48(%rdi),%ah
   6:	0f b9 3a             	ud1    (%rdx),%edi
   9:	eb 4a                	jmp    0x55
   b:	e8 f8 2b 23 fd       	call   0xfd232c08
  10:	48 8d 3d 61 e3 f1 0a 	lea    0xaf1e361(%rip),%rdi        # 0xaf1e378
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 e5 2b 23 fd       	call   0xfd232c08
  23:	48 8d 3d 5e e3 f1 0a 	lea    0xaf1e35e(%rip),%rdi        # 0xaf1e388
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 d2 2b 23 fd       	call   0xfd232c08
  36:	48 8d 3d 5b e3 f1 0a 	lea    0xaf1e35b(%rip),%rdi        # 0xaf1e398
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf