Soft lockup occurs in the NFS delegation recovery code

Issue

• Soft lockup occurs with below log:

  [1724834.494631] NMI watchdog: BUG: soft lockup - CPU#60 stuck for 23s! [192.168.1.1-man:38898]
  [1724834.494637] Modules linked in: tcp_lp fuse rpcsec_gss_krb5 nfsv4 nfs fscache vmw_vsock_vmci_transport vsock ppdev vmw_balloon sb_edac iosf_mbi crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd pcspkr joydev sg parport_pc parport nfit libnvdimm vmw_vmci i2c_piix4 shpchp nfsd auth_rpcgss nfs_acl rbd lockd grace libceph sunrpc dns_resolver binfmt_misc ip_tables xfs libcrc32c sr_mod cdrom ata_generic sd_mod crc_t10dif pata_acpi crct10dif_generic vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm ata_piix crct10dif_pclmul crct10dif_common crc32c_intel libata serio_raw i2c_core vmxnet3 vmw_pvscsi floppy dm_mirror dm_region_hash dm_log dm_mod
  [1724834.494716] CPU: 60 PID: 38898 Comm: 192.168.1.1-man Kdump: loaded Not tainted 3.10.0-862.el7.x86_64 #1
  [1724834.494718] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/05/2016
  [1724834.494721] task: ffff8b2b74f19fa0 ti: ffff8b2a1d22c000 task.ti: ffff8b2a1d22c000
  [1724834.494724] RIP: 0010:[<ffffffff94115670>]  [<ffffffff94115670>] _raw_spin_lock+0x10/0x30
  [1724834.494736] RSP: 0018:ffff8b2a1d22fd70  EFLAGS: 00000246
  [1724834.494738] RAX: 0000000000000000 RBX: 0000000000000246 RCX: ffff8b7fdd570000
  [1724834.494740] RDX: 0000000000000001 RSI: 0000000000000007 RDI: ffff8ad2bb2a1ef8
  [1724834.494742] RBP: ffff8b2a1d22fd88 R08: ffff8b7fdd57488c R09: ffffffff93b969c7
  [1724834.494744] R10: ffff8b7fe225bac0 R11: ffffd9af7008d980 R12: 0000000000001400
  [1724834.494746] R13: ffff8b7fd9c4e548 R14: 0000000000000000 R15: ffffffff93ab1391
  [1724834.494748] FS:  0000000000000000(0000) GS:ffff8b7fe2240000(0000) knlGS:0000000000000000
  [1724834.494749] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  [1724834.494751] CR2: 00007f75939c6000 CR3: 000000606f7ce000 CR4: 00000000003607e0
  [1724834.494798] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  [1724834.494800] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  [1724834.494801] Call Trace:
  [1724834.494809]  [<ffffffff93c37a8e>] ? igrab+0x1e/0x60
  [1724834.494828]  [<ffffffffc07f69aa>] nfs_delegation_grab_inode+0x2a/0x50 [nfsv4]
  [1724834.494837]  [<ffffffffc07f7d2c>] nfs_delegation_reap_unclaimed+0xac/0x140 [nfsv4]
  [1724834.494844]  [<ffffffffc07f2038>] nfs4_state_clear_reclaim_reboot+0x138/0x160 [nfsv4]
  [1724834.494850]  [<ffffffffc07f4170>] nfs4_state_manager+0x5d0/0x8d0 [nfsv4]
  [1724834.494856]  [<ffffffffc07f4470>] ? nfs4_state_manager+0x8d0/0x8d0 [nfsv4]
  [1724834.494861]  [<ffffffffc07f448f>] nfs4_run_state_manager+0x1f/0x40 [nfsv4]
  [1724834.494869]  [<ffffffff93abae31>] kthread+0xd1/0xe0
  [1724834.494871]  [<ffffffff93abad60>] ? insert_kthread_work+0x40/0x40
  [1724834.494875]  [<ffffffff9411f637>] ret_from_fork_nospec_begin+0x21/0x21
  [1724834.494878]  [<ffffffff93abad60>] ? insert_kthread_work+0x40/0x40
  [1724834.494879] Code: 44 00 00 85 d2 74 e4 0f 1f 40 00 eb ed 66 0f 1f 44 00 00 b8 01 00 00 00 5d c3 90 0f 1f 44 00 00 31 c0 ba 01 00 00 00 f0 0f b1 17 <85> c0 75 01 c3 55 89 c6 48 89 e5 e8 9f 2d ff ff 5d c3 0f 1f 40 
  

• [<NFS server's IP address>-manager] kernel thread consumes 100% CPU resource.