Why system gets crash shortly after restarting iptables service ?

Issue

• When iptables service is restarted, system is getting crash with below traces.

ip_tables: (C) 2000-2006 Netfilter Core Team
BUG: unable to handle kernel NULL pointer dereference at 000000000000003e
IP: [<ffffffffa01fef3c>] nf_nat_setup_info+0x55c/0x670 [nf_nat]
PGD 0 
Oops: 0000 [#1] SMP 
last sysfs file: /sys/module/ip_tables/initstate
CPU 0 
Modules linked in: iptable_filter ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables ipt_REJECT ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack xt_multiport ip6table_filter ip6_tables ipv6 power_meter iTCO_wdt iTCO_vendor_support dcdbas serio_raw lpc_ich mfd_core ses enclosure sg i7core_edac edac_core e1000e ptp pps_core bnx2 ext4 jbd2 mbcache sr_mod cdrom sd_mod crc_t10dif pata_acpi ata_generic ata_piix megaraid_sas wmi dm_mirror dm_region_hash dm_log dm_mod [last unloaded: nf_defrag_ipv4]

Pid: 0, comm: swapper Not tainted 2.6.32-431.5.1.el6.x86_64 #1 Dell Inc. PowerEdge R610/0F0XJ6
RIP: 0010:[<ffffffffa01fef3c>]  [<ffffffffa01fef3c>] nf_nat_setup_info+0x55c/0x670 [nf_nat]
RSP: 0018:ffff880053603720  EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff880c713fdd10 RCX: 0000000000000011
RDX: 0000000000000011 RSI: ffff880c735afaa8 RDI: 0000000028e25985
RBP: ffff8800536037f0 R08: 00000000463ce0c4 R09: 0000000000000002
R10: ffff880c6f0f1508 R11: ffff880053603938 R12: 0000000000000000
R13: ffff880053603800 R14: ffff880053603760 R15: ffff8806fba92770
FS:  0000000000000000(0000) GS:ffff880053600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 000000000000003e CR3: 0000000c7281d000 CR4: 00000000000007f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process swapper (pid: 0, threadinfo ffffffff81a00000, task ffffffff81a8d020)
Stack:
 ffff8802fde69380 ffffffff81b18540 ffff880053616840 0000000000000000
<d> 0000000000000000 ffff8800536168a8 ffff8800536168d8 ffff8800536168a8
<d> ffff880c7028d538 000000000083ec45 ffff880c7028d500 0000000000000000
Call Trace:
 <IRQ> 
 [<ffffffff81068ff5>] ? enqueue_entity+0x125/0x450
 [<ffffffffa00b01ef>] masquerade_tg+0xcf/0xec [ipt_MASQUERADE]
 [<ffffffffa008520b>] ipt_do_table+0x3cb/0x678 [ip_tables]
 [<ffffffff81065e02>] ? default_wake_function+0x12/0x20
 [<ffffffff81054839>] ? __wake_up_common+0x59/0x90
 [<ffffffffa021f224>] nf_nat_rule_find+0x24/0x80 [iptable_nat]
 [<ffffffffa021f4c1>] nf_nat_fn+0x111/0x260 [iptable_nat]
 [<ffffffffa021f738>] nf_nat_out+0x48/0xd0 [iptable_nat]
 [<ffffffff814895f9>] nf_iterate+0x69/0xb0
 [<ffffffff8149a2a0>] ? ip_finish_output+0x0/0x310
 [<ffffffff814897b6>] nf_hook_slow+0x76/0x120
 [<ffffffff8149a2a0>] ? ip_finish_output+0x0/0x310
 [<ffffffff8149a654>] ip_output+0xa4/0xc0
 [<ffffffff814958ef>] ip_forward_finish+0x4f/0x60
 [<ffffffff81495afc>] ip_forward+0x1fc/0x430
 [<ffffffff81493c1d>] ip_rcv_finish+0x12d/0x440
 [<ffffffff814941a5>] ip_rcv+0x275/0x350
 [<ffffffff8145b74b>] __netif_receive_skb+0x4ab/0x750
 [<ffffffff8145f3b8>] netif_receive_skb+0x58/0x60
 [<ffffffff8145f4c0>] napi_skb_finish+0x50/0x70
 [<ffffffff81460c29>] napi_gro_receive+0x39/0x50
 [<ffffffffa01353af>] bnx2_poll_work+0xdef/0x1290 [bnx2]
 [<ffffffff810149b9>] ? read_tsc+0x9/0x20
 [<ffffffff810a17a0>] ? __blocking_notifier_call_chain+0x20/0x80
 [<ffffffff812987a0>] ? swiotlb_map_page+0x0/0x100
 [<ffffffff814500a0>] ? __alloc_skb+0x50/0x180
 [<ffffffffa013588d>] bnx2_poll_msix+0x3d/0xc0 [bnx2]
 [<ffffffff81460d43>] net_rx_action+0x103/0x2f0
 [<ffffffff8107a8e1>] __do_softirq+0xc1/0x1e0
 [<ffffffff810e6eb0>] ? handle_IRQ_event+0x60/0x170
 [<ffffffff8100c30c>] call_softirq+0x1c/0x30
 [<ffffffff8100fa75>] do_softirq+0x65/0xa0
 [<ffffffff8107a795>] irq_exit+0x85/0x90
 [<ffffffff815312f5>] do_IRQ+0x75/0xf0
 [<ffffffff8100b9d3>] ret_from_intr+0x0/0x11
 <EOI> 
 [<ffffffff812e09ae>] ? intel_idle+0xde/0x170
 [<ffffffff812e0991>] ? intel_idle+0xc1/0x170
 [<ffffffff814268f7>] cpuidle_idle_call+0xa7/0x140
 [<ffffffff81009fc6>] cpu_idle+0xb6/0x110
 [<ffffffff8150cf1a>] rest_init+0x7a/0x80
 [<ffffffff81c26f8f>] start_kernel+0x424/0x430
 [<ffffffff81c2633a>] x86_64_start_reservations+0x125/0x129
 [<ffffffff81c26453>] x86_64_start_kernel+0x115/0x124
Code: 03 49 03 b7 78 02 00 00 4c 8b 3e 4d 85 ff 75 17 e9 f0 00 00 00 66 2e 0f 1f 84 00 00 00 00 00 4d 8b 3f 4d 85 ff 74 68 49 8b 47 20 <38> 50 3e 75 ef 8b 48 18 3b 4d a0 75 e7 0f b7 48 28 66 3b 4d b0 
RIP  [<ffffffffa01fef3c>] nf_nat_setup_info+0x55c/0x670 [nf_nat]
 RSP <ffff880053603720>
CR2: 000000000000003e

• For some systems modprobe process can show 100% CPU while stopping iptables service. The process will not get kill with command #kill -9 as well.

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                          
38447 root      20   0  4160  604  536 R 100.0  0.0   1092:06 modprobe   

• How to resolve this ?