Kernel crashes in block layer while using third party `ibmrbrdtc` driver

Issue

• System crashed and logged below stack while using proprietary driver ibmrbrdtc.

[  129.732379] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
[  129.732387] PGD 22436d067 P4D 22436d067 PUD 2b44ea067 PMD 0 
[  129.732396] Oops: 0000 [#1] SMP NOPTI
[  129.732402] CPU: 1 PID: 2529 Comm: dtcoverride Kdump: loaded Tainted: P           OE    --------- -  - 4.18.0-305.el8.x86_64 #1
[  129.732406] Hardware name: VMware, Inc. VMware7,1/440BX Desktop Reference Platform, BIOS VMW71.00V.13989454.B64.1906190538 06/19/2019
[  129.732418] RIP: 0010:blk_throtl_bio+0x52/0xb30
[  129.732424] Code: bc c7 60 02 00 00 0f b7 43 14 f6 c4 02 0f 85 07 05 00 00 48 8b 43 08 8b 6b 10 4c 8b a0 20 05 00 00 89 e8 83 e0 01 89 44 24 40 <49> 8b 47 28 48 89 44 24 10 e9 80 01 00 00 4c 63 6c 24 40 43 0f b6
[  129.732428] RSP: 0018:ffffb75c83e33bb8 EFLAGS: 00010202
[  129.732432] RAX: 0000000000000001 RBX: ffff99fd831a9800 RCX: 00000000001ffff8
[  129.732435] RDX: ffffffff8d022440 RSI: 0000000000200000 RDI: ffff99fd831a9800
[  129.732438] RBP: 0000000000000801 R08: 0000000000000000 R09: ffff99fdb506e060
[  129.732441] R10: 0000000000000000 R11: ffffffffb2a582c8 R12: ffff99fdf1f9eeb0
[  129.732443] R13: ffff99fdf2a35000 R14: 0000000000001000 R15: 0000000000000000
[  129.732448] FS:  00007f0698bcf540(0000) GS:ffff99fdf5d00000(0000) knlGS:0000000000000000
[  129.732451] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  129.732454] CR2: 0000000000000028 CR3: 0000000206bfa002 CR4: 00000000003706e0
[  129.732868] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  129.732872] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  129.732875] Call Trace:
[  129.732887]  ? work_busy+0x80/0x80
[  129.732894]  generic_make_request_checks+0x17b/0x540
[  129.732901]  generic_make_request+0x30/0x340
[  129.732919]  ? hash_table_get+0x46/0x50 [ibmrbrdtc]
[  129.732931]  ftd_dynamic_activation_initiate_io_to_a_possibly_captured_device+0x9f/0xa8 [ibmrbrdtc]
[  129.732943]  bio_write_page+0xfd/0x108 [ibmrbrdtc]
[  129.732953]  ftd_write_lrdb+0x2a/0x59 [ibmrbrdtc]
[  129.732964]  ftd_ctl_set_group_state+0xc31/0xc89 [ibmrbrdtc]
[  129.732972]  ? _cond_resched+0x15/0x30
[  129.732982]  ? ftd_char_ioctl+0x67/0x130 [ibmrbrdtc]
[  129.732990]  ? __kmalloc+0x102/0x240
[  129.732999]  ftd_char_ioctl+0xb1/0x130 [ibmrbrdtc]
[  129.733008]  ftd_char_unlocked_ioctl+0x36/0x39 [ibmrbrdtc]
[  129.733018]  do_vfs_ioctl+0xa4/0x680
[  129.733027]  ? syscall_trace_enter+0x1d3/0x2c0
[  129.733033]  ksys_ioctl+0x60/0x90
[  129.733039]  __x64_sys_ioctl+0x16/0x20
[  129.733045]  do_syscall_64+0x5b/0x1a0
[  129.733052]  entry_SYSCALL_64_after_hwframe+0x65/0xca
[  129.733057] RIP: 0033:0x7f06986de62b
[  129.733062] Code: 0f 1e fa 48 8b 05 5d b8 2c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 2d b8 2c 00 f7 d8 64 89 01 48
[  129.733066] RSP: 002b:00007ffcef4a8258 EFLAGS: 00000202 ORIG_RAX: 0000000000000010
[  129.733070] RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00007f06986de62b
[  129.733073] RDX: 00007ffcef4a8260 RSI: 00000000c0107132 RDI: 0000000000000004
[  129.733076] RBP: 0000000000000002 R08: 0000000000411000 R09: 0000000000000000
[  129.733078] R10: 0000000000000003 R11: 0000000000000202 R12: 0000000000000002
[  129.733080] R13: 0000000000000002 R14: 0000000000000000 R15: 00007ffcef4aa6b9
[  129.733085] Modules linked in: vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock sunrpc intel_rapl_msr intel_rapl_common isst_if_mbox_msr isst_if_common nfit libnvdimm crct10dif_pclmul crc32_pclmul vmw_balloon ghash_clmulni_intel rapl joydev pcspkr vmw_vmci i2c_piix4 ibmrbrdtc(POE) vfat fat ip_tables ext4 mbcache jbd2 sr_mod cdrom ata_generic vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm sd_mod t10_pi sg drm ahci libahci ata_piix crc32c_intel libata serio_raw vmw_pvscsi vmxnet3 fuse
[  129.733187] CR2: 0000000000000028