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: syz.6.3472/23205
Modules linked in:
CPU: 0 UID: 0 PID: 23205 Comm: syz.6.3472 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
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: 34 37 89 0b 67 48 0f b9 3a eb 4a e8 38 ee 13 fd 48 8d 3d 31 37 89 0b 67 48 0f b9 3a eb 37 e8 25 ee 13 fd 48 8d 3d 2e 37 89 0b <67> 48 0f b9 3a eb 24 e8 12 ee 13 fd 48 8d 3d 2b 37 89 0b 67 48 0f
RSP: 0018:ffffc90000007c68 EFLAGS: 00010246
RAX: ffffffff84b1c9ab RBX: 0000000000000003 RCX: ffff8880340c3e00
RDX: 0000000000000100 RSI: ffffffff8f110f80 RDI: ffffffff903b00e0
RBP: ffffc90000007d70 R08: ffff8880340c3e00 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000100 R12: 0000000000000000
R13: 0000000100024f05 R14: ffff8880296fa020 R15: ffff8880296fa1b8
FS:  0000000000000000(0000) GS:ffff88812529f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7c32bb544c CR3: 0000000060a25000 CR4: 0000000000350ef0
Call Trace:
 <IRQ>
 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+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+0x22a/0x840 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1061
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:pfn_valid+0x1c/0x480 arch/x86/include/asm/cpufeature.h:-1
Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 41 57 41 56 41 55 41 54 53 49 89 fe e8 2e 13 89 ff e9 f3 03 00 00 e8 24 13 89 ff <49> bc 00 00 00 00 00 fc ff df e9 18 04 00 00 e8 10 13 89 ff 48 c7
RSP: 0018:ffffc9000454f318 EFLAGS: 00000293
RAX: ffffffff823ca8ba RBX: 0000000000000001 RCX: ffff8880340c3e00
RDX: 0000000000000000 RSI: 0000000000153fb6 RDI: 0000000400000000
RBP: ffffc9000454f690 R08: ffffea00054fed87 R09: 1ffffd4000a9fdb0
R10: dffffc0000000000 R11: fffff94000a9fdb1 R12: dffffc0000000000
R13: 8000000153fb6007 R14: 0000000000153fb6 R15: 0000000000153fb6
 page_table_check_clear+0x21/0x4f0 mm/page_table_check.c:70
 ptep_get_and_clear_full arch/x86/include/asm/jump_label.h:-1 [inline]
 get_and_clear_full_ptes include/linux/pgtable.h:845 [inline]
 zap_present_folio_ptes mm/memory.c:1648 [inline]
 zap_present_ptes mm/memory.c:1730 [inline]
 do_zap_pte_range mm/memory.c:1832 [inline]
 zap_pte_range mm/memory.c:1934 [inline]
 zap_pmd_range mm/memory.c:2020 [inline]
 zap_pud_range mm/memory.c:2048 [inline]
 zap_p4d_range mm/memory.c:2069 [inline]
 __zap_vma_range+0x365c/0x4b70 mm/memory.c:2109
 unmap_vmas+0x3ac/0x570 mm/memory.c:2178
 exit_mmap+0x280/0x9e0 mm/mmap.c:1300
 __mmput+0x118/0x430 kernel/fork.c:1178
 exit_mm+0x1f6/0x2d0 kernel/exit.c:582
 do_exit+0x6a2/0x22c0 kernel/exit.c:964
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1119
 get_signal+0x1284/0x1330 kernel/signal.c:3037
 arch_do_signal_or_restart+0xbc/0x840 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0xa9/0x680 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x353/0x580 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe12f39ce59
Code: Unable to access opcode bytes at 0x7fe12f39ce2f.
RSP: 002b:00007fe1301960e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007fe12f615fa8 RCX: 00007fe12f39ce59
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fe12f615fa8
RBP: 00007fe12f615fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe12f616038 R14: 00007ffe2e129c90 R15: 00007ffe2e129d78
 </TASK>
----------------
Code disassembly (best guess):
   0:	34 37                	xor    $0x37,%al
   2:	89 0b                	mov    %ecx,(%rbx)
   4:	67 48 0f b9 3a       	ud1    (%edx),%rdi
   9:	eb 4a                	jmp    0x55
   b:	e8 38 ee 13 fd       	call   0xfd13ee48
  10:	48 8d 3d 31 37 89 0b 	lea    0xb893731(%rip),%rdi        # 0xb893748
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 25 ee 13 fd       	call   0xfd13ee48
  23:	48 8d 3d 2e 37 89 0b 	lea    0xb89372e(%rip),%rdi        # 0xb893758
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 12 ee 13 fd       	call   0xfd13ee48
  36:	48 8d 3d 2b 37 89 0b 	lea    0xb89372b(%rip),%rdi        # 0xb893768
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf