linux 5.15-rc4: refcount underflow when unloading gpio-mockup

[Kent Gibson]

Hi,

I'm seeing a refcount underflow when I unload the gpio-mockup module on
Linux v5.15-rc4 (and going back to v5.15-rc1):

# modprobe gpio-mockup gpio_mockup_ranges=-1,4,-1,10
# rmmod gpio-mockup
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 103 at lib/refcount.c:28 refcount_warn_saturate+0xd1/0x120
Modules linked in: gpio_mockup(-)
CPU: 0 PID: 103 Comm: rmmod Not tainted 5.15.0-rc4 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
EIP: refcount_warn_saturate+0xd1/0x120
Code: e8 a2 b0 3b 00 0f 0b eb 83 80 3d db 2a 8c c1 00 0f 85 76 ff ff ff c7 04 24 88 85 78 c1 b1 01 88 0d db 2a 8c c1 e8 7d b0 3b 00 <0f> 0b e9 5b ff ff ff 80 3d d9 2a 8c c1 00 0f 85 4e ff ff ff c7 04
EAX: 00000026 EBX: c250b100 ECX: f5fe8c28 EDX: 00000000
ESI: c244860c EDI: c250b100 EBP: c245be84 ESP: c245be80
DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 EFLAGS: 00000296
CR0: 80050033 CR2: b7e3c3e1 CR3: 024ba000 CR4: 00000690
Call Trace:
 kobject_put+0xdc/0xf0
 software_node_notify_remove+0xa8/0xc0
 device_del+0x15a/0x3e0
 ? kfree_const+0xf/0x30
 ? kobject_put+0xa6/0xf0
 ? module_remove_driver+0x73/0xa0
 platform_device_del.part.0+0xf/0x80
 platform_device_unregister+0x19/0x40
 gpio_mockup_unregister_pdevs+0x13/0x1b [gpio_mockup]
 gpio_mockup_exit+0x1c/0x68c [gpio_mockup]
 __ia32_sys_delete_module+0x137/0x1e0
 ? task_work_run+0x61/0x90
 ? exit_to_user_mode_prepare+0x1b5/0x1c0
 __do_fast_syscall_32+0x50/0xc0
 do_fast_syscall_32+0x32/0x70
 do_SYSENTER_32+0x15/0x20
 entry_SYSENTER_32+0x98/0xe7
EIP: 0xb7eda549
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90 8d 76
EAX: ffffffda EBX: 0045a19c ECX: 00000800 EDX: 0045a160
ESI: fffffffe EDI: 0045a160 EBP: bff19d08 ESP: bff19cc8
DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000202
---[ end trace 3d71387f54bc2d06 ]---

I suspect this is related to the recent changes to swnode.c or
platform.c, as gpio-mockup hasn't changed, but haven't had the
chance to debug further.

Cheers,
Kent.