------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#1: syz.5.1200/10011
Modules linked in:
CPU: 1 UID: 0 PID: 10011 Comm: syz.5.1200 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+0xb2/0x110 lib/refcount.c:28
Code: 24 0b a7 0b 67 48 0f b9 3a eb 4a e8 58 96 e9 fc 48 8d 3d 21 0b a7 0b 67 48 0f b9 3a eb 37 e8 45 96 e9 fc 48 8d 3d 1e 0b a7 0b <67> 48 0f b9 3a eb 24 e8 32 96 e9 fc 48 8d 3d 1b 0b a7 0b 67 48 0f
RSP: 0018:ffffc90000a18c68 EFLAGS: 00010246
RAX: ffffffff84de24db RBX: 0000000000000003 RCX: ffff888028633e80
RDX: 0000000000000100 RSI: 0000000000000100 RDI: ffffffff90853000
RBP: ffffc90000a18d70 R08: ffff888028633e80 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000100 R12: 0000000000000001
R13: 0000000100000c09 R14: ffff88802778c020 R15: ffff88802778c1b8
FS:  00007f6dd8db86c0(0000) GS:ffff888124dd9000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000002480 CR3: 0000000058f3c000 CR4: 00000000003526f0
DR0: ffffffffffffffff DR1: 20000000000001f8 DR2: 0000000000000002
DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 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:767
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:784
 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_irq include/linux/spinlock_api_smp.h:220 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x29/0x50 kernel/locking/spinlock.c:229
Code: 90 f3 0f 1e fa 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 1a 4d bc f5 48 89 df e8 d2 c4 bc f5 e8 cd 01 e9 f5 fb bf 01 00 00 00 <e8> 82 de ad f5 65 48 8b 05 2a 71 ad 07 48 85 c0 74 07 5b c3 cc cc
RSP: 0018:ffffc900050a7350 EFLAGS: 00000202
RAX: 0000000000001cd9 RBX: ffff888031430f78 RCX: 8000000000000001
RDX: 0000000000000007 RSI: ffffffff8e474a01 RDI: 0000000000000001
RBP: ffffc900050a74b0 R08: ffffffff907a167f R09: 1ffffffff20f42cf
R10: dffffc0000000000 R11: fffffbfff20f42d0 R12: dffffc0000000000
R13: ffffc900050a7400 R14: 0000000000000000 R15: 0000000000000001
 spin_unlock_irq include/linux/spinlock.h:413 [inline]
 shmem_add_to_page_cache+0xa5e/0xd40 mm/shmem.c:939
 shmem_alloc_and_add_folio+0x854/0xf60 mm/shmem.c:2001
 shmem_get_folio_gfp+0x5da/0x16d0 mm/shmem.c:2528
 shmem_fault+0x179/0x390 mm/shmem.c:2729
 __do_fault+0x138/0x2a0 mm/memory.c:5565
 do_read_fault mm/memory.c:6000 [inline]
 do_fault mm/memory.c:6134 [inline]
 do_pte_missing+0x2215/0x34b0 mm/memory.c:4700
 handle_pte_fault mm/memory.c:6558 [inline]
 __handle_mm_fault mm/memory.c:6707 [inline]
 handle_mm_fault+0x1a53/0x3750 mm/memory.c:6876
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0x1675/0x2750 mm/gup.c:1428
 populate_vma_page_range+0x2be/0x3c0 mm/gup.c:1860
 __mm_populate+0x25f/0x390 mm/gup.c:1963
 mm_populate include/linux/mm.h:4288 [inline]
 vm_mmap_pgoff+0x353/0x4e0 mm/util.c:586
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6dd7f9e159
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:00007f6dd8db8028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f6dd8225fa0 RCX: 00007f6dd7f9e159
RDX: 0000000000000002 RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007f6dd8035024 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6dd8226038 R14: 00007f6dd8225fa0 R15: 00007f6dd834fa48
 </TASK>
----------------
Code disassembly (best guess):
   0:	24 0b                	and    $0xb,%al
   2:	a7                   	cmpsl  %es:(%rdi),%ds:(%rsi)
   3:	0b 67 48             	or     0x48(%rdi),%esp
   6:	0f b9 3a             	ud1    (%rdx),%edi
   9:	eb 4a                	jmp    0x55
   b:	e8 58 96 e9 fc       	call   0xfce99668
  10:	48 8d 3d 21 0b a7 0b 	lea    0xba70b21(%rip),%rdi        # 0xba70b38
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 45 96 e9 fc       	call   0xfce99668
  23:	48 8d 3d 1e 0b a7 0b 	lea    0xba70b1e(%rip),%rdi        # 0xba70b48
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 32 96 e9 fc       	call   0xfce99668
  36:	48 8d 3d 1b 0b a7 0b 	lea    0xba70b1b(%rip),%rdi        # 0xba70b58
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf