NFSv4 client crashes at decode_sequence due to unable to handle kernel NULL pointer dereference at 0000000000000000

Issue

• An NFSv4 client crashes with the following messages.

[1823367.821194] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
[1823367.821201] PGD 0 P4D 0 
[1823367.821204] Oops: 0000 [#1] SMP PTI
[1823367.821207] CPU: 0 PID: 2677939 Comm: kworker/u8:0 Kdump: loaded Tainted: P           OE    --------- -  - 4.18.0-80.el8.x86_64 #1
[1823367.821209] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 12/12/2018
[1823367.821239] Workqueue: rpciod rpc_async_schedule [sunrpc]
[1823367.821257] RIP: 0010:decode_sequence.isra.43.part.44+0x85/0x140 [nfsv4]
[1823367.821259] Code: 00 00 00 48 8d 65 e8 5b 41 5c 41 5d 5d c3 ba 10 00 00 00 48 8d 74 24 10 4c 89 ef e8 25 a7 ff ff 89 c3 85 c0 75 c2 49 8b 04 24 <48> 8b 00 48 8b 00 48 8b 08 48 39 4c 24 10 74 14 f6 05 2c f5 c7 ff
[1823367.821260] RSP: 0018:ffffa8468487fcd0 EFLAGS: 00010246
[1823367.821262] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000008
[1823367.821263] RDX: 0000000000000008 RSI: ffffa8468487fce8 RDI: 0000000000000000
[1823367.821265] RBP: ffffa8468487fd20 R08: 0000002b12345678 R09: 0000000000000000
[1823367.821266] R10: 8080808080808080 R11: 0000000000000000 R12: ffff896206c62ca8
[1823367.821267] R13: ffffa8468487fd90 R14: ffff89634a474d2c R15: ffffffffc068d940
[1823367.821269] FS:  0000000000000000(0000) GS:ffff896437a00000(0000) knlGS:0000000000000000
[1823367.821270] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[1823367.821272] CR2: 0000000000000000 CR3: 00000001bd80a005 CR4: 00000000007606f0
[1823367.821302] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[1823367.821303] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[1823367.821304] PKRU: 55555554
[1823367.821305] Call Trace:
[1823367.821328]  ? nfs4_xdr_dec_open+0x120/0x120 [nfsv4]
[1823367.821337]  ? nfs4_xdr_dec_open+0x120/0x120 [nfsv4]
[1823367.821345]  nfs4_xdr_dec_open_noattr+0x53/0x100 [nfsv4]
[1823367.821353]  ? pty_write+0x78/0x90
[1823367.821358]  ? tty_put_char+0x3c/0x50
[1823367.821367]  rpcauth_unwrap_resp+0xad/0xc0 [sunrpc]
[1823367.821377]  ? nfs4_xdr_dec_open+0x120/0x120 [nfsv4]
[1823367.821383]  call_decode+0x20a/0x4e0 [sunrpc]
[1823367.821395]  ? trace_event_raw_event_rpc_stats_latency+0x240/0x240 [sunrpc]
[1823367.821401]  ? call_refreshresult+0xd0/0xd0 [sunrpc]
[1823367.821409]  __rpc_execute+0x7f/0x340 [sunrpc]
[1823367.821417]  process_one_work+0x1a7/0x360
[1823367.821423]  worker_thread+0x30/0x390
[1823367.821426]  ? pwq_unbound_release_workfn+0xd0/0xd0
[1823367.821429]  kthread+0x112/0x130
[1823367.821435]  ? kthread_bind+0x30/0x30
[1823367.821438]  ret_from_fork+0x35/0x40