Termination condition in assoc array garbage collection can cause the system to crash

Issue

• Seems our systems are rebooting due to a kernel bug
• System is crashing with following oops:

:Version: 3.10.0-123.8.1.el7.x86_64
:BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
:IP: [<ffffffff812cfbd7>] assoc_array_gc+0x2f7/0x540
:PGD 0 
:Oops: 0000 [#1] SMP 
:Modules linked in: fuse btrfs zlib_deflate raid6_pq xor vfat msdos fat xfs libcrc32c ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT xt_CHECKSUM iptable_mangle tun bridge stp llc ip6table_filter ip6_tables iptable_filter ip_tables ebtable_nat ebtables nfsv3 nfs fscache snd_hda_codec_hdmi dm_mirror dm_region_hash dm_log dm_mod coretemp kvm_intel iTCO_wdt iTCO_vendor_support kvm snd_hda_codec_realtek crct10dif_pclmul crc32_pclmul snd_hda_codec_generic crc32c_intel ghash_clmulni_intel dcdbas snd_hda_intel aesni_intel lrw gf128mul nvidia(POF) glue_helper ablk_helper cryptd snd_hda_codec pcspkr serio_raw snd_hwdep sb_edac snd_seq edac_core snd_seq_device snd_pcm i2c_i801 snd_page_alloc snd_timer snd lpc_ich drm mfd_core mei_me
: soundcore mei i2c_core ntb shpchp usb_storage mperf nfsd auth_rpcgss nfs_acl lockd sunrpc uinput binfmt_misc ext4 mbcache jbd2 sd_mod sr_mod crc_t10dif cdrom crct10dif_common isci ahci libahci libsas e1000e scsi_transport_sas libata ptp pps_core
:CPU: 0 PID: 11518 Comm: kworker/0:0 Tainted: PF          O--------------   3.10.0-123.8.1.el7.x86_64 #1
:Hardware name: Dell Inc. Precision T3600/08HPGT, BIOS A07 11/08/2012
:Workqueue: events key_garbage_collector
:task: ffff88081f95e660 ti: ffff880036234000 task.ti: ffff880036234000
:RIP: 0010:[<ffffffff812cfbd7>]  [<ffffffff812cfbd7>] assoc_array_gc+0x2f7/0x540
:RSP: 0018:ffff880036235d40  EFLAGS: 00010206
:RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000108ca5
:RDX: ffff880669342060 RSI: 0000000000000001 RDI: ffff880036c57d80
:RBP: ffff880036235da8 R08: 0000000000000001 R09: 0000000000000003
:R10: ffffea002086d000 R11: ffffffff812cfb45 R12: 0000000000000000
:R13: 0000000000000000 R14: 0000000000000013 R15: 0000000000000001
:FS:  0000000000000000(0000) GS:ffff88082f200000(0000) knlGS:0000000000000000
:CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
:CR2: 0000000000000018 CR3: 00000000018d0000 CR4: 00000000000407f0
:DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
:DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
:Stack:
: 00000000000000fe 0000000000000003 ffff880036235db8 ffffffff81245b90
: ffff880815eb9c00 0000000000000000 ffff880036c57d83 0000000078cd5470
: ffff8808236a47a0 ffff8808236a4820 0000000054504b5e ffff880036235fd8
:Call Trace:
: [<ffffffff81245b90>] ? keyring_detect_cycle_iterator+0x30/0x30
: [<ffffffff81246f75>] keyring_gc+0x75/0x80
: [<ffffffff8124454f>] key_garbage_collector+0x17f/0x390
: [<ffffffff8107e03b>] process_one_work+0x17b/0x460
: [<ffffffff8107ee0b>] worker_thread+0x11b/0x400
: [<ffffffff8107ecf0>] ? rescuer_thread+0x400/0x400
: [<ffffffff81085aff>] kthread+0xcf/0xe0
: [<ffffffff81085a30>] ? kthread_create_on_node+0x140/0x140
: [<ffffffff815f29ac>] ret_from_fork+0x7c/0xb0
: [<ffffffff81085a30>] ? kthread_create_on_node+0x140/0x140
:Code: 08 4c 8b 22 0f 84 bf 00 00 00 41 83 c7 01 49 83 e4 fc 41 83 ff 0f 4c 89 65 c0 0f 8f 5a fe ff ff 48 8b 45 c0 4d 63 cf 49 83 c1 02 <4e> 8b 34 c8 4d 85 f6 0f 84 be 00 00 00 41 f6 c6 01 0f 84 92 00 
:RIP  [<ffffffff812cfbd7>] assoc_array_gc+0x2f7/0x540
: RSP <ffff880036235d40>