refcount_t: addition on 0; use-after-free.
------------[ cut here ]------------
kernel BUG at lib/refcount.c:34!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 5930 Comm: syz-executor856 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
RIP: 0010:refcount_warn_saturate+0xf0/0x110 lib/refcount.c:34
Code: 80 c1 03 38 c1 0f 8c 6a ff ff ff 4c 89 f7 e8 d7 92 63 fd e9 5d ff ff ff e8 ad b2 f6 fc 48 c7 c7 60 82 ea 8b e8 11 5c 57 fc 90 <0f> 0b e8 99 b2 f6 fc 48 c7 c7 e0 82 ea 8b e8 fd 5b 57 fc 90 0f 0b
RSP: 0018:ffffc90004a37928 EFLAGS: 00010246
RAX: 000000000000002a RBX: 0000000000000002 RCX: 3a69e62f58ffd700
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90004a37be8 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52000946ed5 R12: ffffea0001610000
R13: dffffc0000000000 R14: ffff888036ec0c01 R15: ffff88803af58430
FS:  000055558950d4c0(0000) GS:ffff8881247ad000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa042400000 CR3: 000000003486e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:-1 [inline]
 __refcount_inc include/linux/refcount.h:366 [inline]
 refcount_inc include/linux/refcount.h:383 [inline]
 kref_get include/linux/kref.h:45 [inline]
 hugetlb_unmap_file_folio fs/hugetlbfs/inode.c:413 [inline]
 remove_inode_single_folio fs/hugetlbfs/inode.c:512 [inline]
 remove_inode_hugepages+0xbdb/0x10f0 fs/hugetlbfs/inode.c:577
 hugetlb_vmtruncate fs/hugetlbfs/inode.c:621 [inline]
 hugetlbfs_setattr+0x4f0/0x6d0 fs/hugetlbfs/inode.c:856
 notify_change+0xbb8/0xec0 fs/attr.c:556
 do_truncate+0x1c2/0x250 fs/open.c:68
 do_ftruncate+0x4e0/0x590 fs/open.c:194
 ksys_ftruncate fs/open.c:206 [inline]
 __do_sys_ftruncate fs/open.c:211 [inline]
 __se_sys_ftruncate fs/open.c:209 [inline]
 __x64_sys_ftruncate+0x8f/0xe0 fs/open.c:209
 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: 0033:0x7fa04350daa7
Code: 00 00 00 48 c7 c0 d0 ff ff ff 64 c7 00 0c 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 4d 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d0 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fffbd25aeb8 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fa04350daa7
RDX: 0000000000000044 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fa0435adb60 R08: 0000000029b4ae16 R09: 3fffffffffffffff
R10: 4000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fffbd25af00 R14: 00007fffbd25aef0 R15: 4ec4ec4ec4ec4ec5
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:refcount_warn_saturate+0xf0/0x110 lib/refcount.c:34
Code: 80 c1 03 38 c1 0f 8c 6a ff ff ff 4c 89 f7 e8 d7 92 63 fd e9 5d ff ff ff e8 ad b2 f6 fc 48 c7 c7 60 82 ea 8b e8 11 5c 57 fc 90 <0f> 0b e8 99 b2 f6 fc 48 c7 c7 e0 82 ea 8b e8 fd 5b 57 fc 90 0f 0b
RSP: 0018:ffffc90004a37928 EFLAGS: 00010246
RAX: 000000000000002a RBX: 0000000000000002 RCX: 3a69e62f58ffd700
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90004a37be8 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52000946ed5 R12: ffffea0001610000
R13: dffffc0000000000 R14: ffff888036ec0c01 R15: ffff88803af58430
FS:  000055558950d4c0(0000) GS:ffff8881247ad000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa042400000 CR3: 000000003486e000 CR4: 00000000003526f0