Description of problem:
Azure ARM RHEL 8.8 use below command to trigger crash -

1. echo 1 > /proc/sys/kernel/sysrq; echo c > /proc/sysrq-trigger

Serial console shows below logs before a restart happens -
[ 36.517830] sysrq: SysRq : Trigger a crash
[ 36.520721] Kernel panic - not syncing: sysrq triggered crash
[ 36.520721]
[ 36.525900] CPU: 1 PID: 1766 Comm: bash Kdump: loaded Tainted: G W --------- - - 4.18.0-447.el8.aarch64 #1
[ 36.533966] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 05/16/2022
[ 36.542059] Call trace:
[ 36.543898] dump_backtrace+0x0/0x178
[ 36.546702] show_stack+0x28/0x38
[ 36.549147] dump_stack+0x5c/0x74
[ 36.551568] panic+0x140/0x30c
[ 36.553861] sysrq_reset_seq_param_set+0x0/0xa8
[ 36.557226] __handle_sysrq+0x9c/0x190
[ 36.559981] write_sysrq_trigger+0x7c/0x98
[ 36.562968] proc_reg_write+0x84/0xd8
[ 36.565670] __vfs_write+0x4c/0x90
[ 36.568121] vfs_write+0xb0/0x1b8
[ 36.570497] ksys_write+0x70/0xd8
[ 36.572884] __arm64_sys_write+0x28/0x38
[ 36.575752] do_el0_svc+0xb4/0x188
[ 36.578249] el0_sync_handler+0x88/0xac
[ 36.581059] el0_sync+0x140/0x180
[ 36.583462] SMP: stopping secondary CPUs
[ 36.586264] Kernel Offset: 0x404bc6d00000 from 0xffff800010000000
[ 36.590470] PHYS_OFFSET: 0xffffa6dc00000000
[ 36.593308] CPU features: 0x0000044a,84814210
[ 36.596941] Memory Limit: none
[ 41.601628] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 46.620415] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 51.636353] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 56.659883] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 61.676422] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 66.695090] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 71.714063] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 76.744787] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 81.762957] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 86.780668] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 91.799017] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 96.823126] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 101.836149] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 106.860822] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 111.875220] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 116.891644] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 121.911215] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 126.924527] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 131.945844] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 136.960236] hv_vmbus: Waiting for VMBus UNLOAD to complete
[ 136.974631] hv_vmbus: Continuing even though VMBus UNLOAD did not complete
[ 136.980798] Starting crashdump kernel...
[ 136.983798] Bye!
[ 0.000000] Booting Linux on physical CPU 0x0000000001 [0x413fd0c1]

Version-Release number of selected component (if applicable):
4.18.0-447.el8.aarch64

How reproducible:
100% when system fully boots.

Steps to Reproduce:
1. Start an Azure ARM RHEL 8.8 VM. Wait for a couple of minutes.
2. # echo 1 > /proc/sys/kernel/sysrq; echo c > /proc/sysrq-trigger
Actual results:
VMBus unload takes a long time before system can reboot.

Expected results:
No such stall.

Additional info:
1. No such issue on RHEL 9.2.
2. No such issue on x86_64 RHEL 8.8.