RHEL8 : panic while breaking a lease/delegation after user mode helper invocation

Issue

Host panics with the following stack :

[   83.642293] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
[   83.642329] PGD 0 P4D 0 
[   83.642338] Oops: 0000 [#1] SMP NOPTI
[   83.642348] CPU: 1 PID: 5425 Comm: kworker/u8:2 Kdump: loaded Not tainted 4.18.0-305.3.1.el8_4.x86_64 #1
[   83.642367] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2.fc34 04/01/2014
[   83.642391] RIP: 0010:kthread_func+0x15/0x20
[   83.642401] Code: 68 10 01 75 b7 48 8b 40 20 e8 07 c1 af 00 eb ac 0f 1f 44 00 00 0f 1f 44 00 00 31 c0 f6 47 26 20 75 01 c3 48 8b 87 d8 09 00 00 <48> 8b 40 10 c3 66 0f 1f 44 00 00 0f 1f 44 00 00 65 48 8b 14 25 
40
[   83.642441] RSP: 0018:ffffb360c12f3b38 EFLAGS: 00010202
[   83.642457] RAX: 0000000000000000 RBX: ffff96c38ff4e738 RCX: ffff96c38d715b88
[   83.642472] RDX: ffff96c38d7120e0 RSI: ffff96c38d7126c0 RDI: ffff96c396528000
[   83.642492] RBP: ffff96c38d7120d8 R08: ffffb360c12f3b38 R09: ffff96c38d7126c0
[   83.642507] R10: ffffb360c12f3c38 R11: 0000000000000000 R12: ffff96c38d7126c0
[   83.642522] R13: ffffffffb5f05d80 R14: 000000008d7126c0 R15: ffff96c3b636c000
[   83.642537] FS:  0000000000000000(0000) GS:ffff96c3bbc80000(0000) knlGS:0000000000000000
[   83.642557] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   83.642570] CR2: 0000000000000010 CR3: 0000000009810004 CR4: 0000000000770ee0
[   83.642587] PKRU: 55555554
[   83.642594] Call Trace:
[   83.642652]  i_am_nfsd+0x13/0x20 [nfsd]
[   83.642680]  nfsd_breaker_owns_lease+0xf/0x40 [nfsd]
[   83.642700]  leases_conflict+0x28/0xd0
[   83.642725]  any_leases_conflict.isra.30+0x37/0x50
[   83.642742]  __break_lease+0xc2/0x510
[   83.642753]  do_dentry_open+0x10d/0x340
[   83.642768]  path_openat+0x53e/0x14f0
[   83.642783]  do_filp_open+0x93/0x100
[   83.642801]  ? kmemdup+0x2d/0x40
[   83.642810]  do_open_execat+0x83/0x1a0
[   83.642821]  do_execveat_common.isra.37+0x1d0/0x8b0
[   83.642833]  ? getname_kernel+0x2c/0x100
[   83.642842]  do_execve+0x1f/0x30
[   83.642852]  call_usermodehelper_exec_async+0xf0/0x150
[   83.642873]  ? recalc_sigpending+0x17/0x50
[   83.642885]  ? call_usermodehelper+0xa0/0xa0
[   83.642897]  ret_from_fork+0x1f/0x40