RHEL 6 NFS client panics when ls done on removed NetApp snapshot

Issue

• NFS client kernel panics when doing an ls in the directory of a snapshot that has already been removed.
• NFS client kernel panics under certain conditions when connected to NFS server either NetApp or Solaris ZFS
• Kernel crashes with message

BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
IP: [<ffffffff81192957>] commit_tree+0x77/0x100
PGD 7ff2e69067 PUD 7feaf59067 PMD 0 
Oops: 0000 [#1] SMP 
last sysfs file: /sys/devices/pci0000:00/0000:00:03.0/0000:07:00.0/vendor
CPU 64 
Modules linked in: nls_utf8 fuse mptctl mptbase autofs4 nfs lockd fscache(T) nfs_acl auth_rpcgss bnx2fc cnic uio fcoe libfcoe libfc scsi_transport_fc scsi_tgt 8021q garp stp llc smbus(U) ipmi_devintf ipmi_si ipmi_msghandler sunrpc cpufreq_ondemand acpi_cpufreq freq_table nf_conntrack_ftp ipt_REJECT ipt_LOG iptable_filter ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables ipv6 vfat fat dm_mirror dm_region_hash dm_log microcode sg i2c_i801 i2c_core iTCO_wdt iTCO_vendor_support ioatdma i7core_edac edac_core ixgbe mdio igb dca ext4 mbcache jbd2 sr_mod cdrom sd_mod crc_t10dif ata_generic pata_acpi ata_piix megaraid_sas dm_mod [last unloaded: scsi_wait_scan]

Modules linked in: nls_utf8 fuse mptctl mptbase autofs4 nfs lockd fscache(T) nfs_acl auth_rpcgss bnx2fc cnic uio fcoe libfcoe libfc scsi_transport_fc scsi_tgt 8021q garp stp llc smbus(U) ipmi_devintf ipmi_si ipmi_msghandler sunrpc cpufreq_ondemand acpi_cpufreq freq_table nf_conntrack_ftp ipt_REJECT ipt_LOG iptable_filter ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables ipv6 vfat fat dm_mirror dm_region_hash dm_log microcode sg i2c_i801 i2c_core iTCO_wdt iTCO_vendor_support ioatdma i7core_edac edac_core ixgbe mdio igb dca ext4 mbcache jbd2 sr_mod cdrom sd_mod crc_t10dif ata_generic pata_acpi ata_piix megaraid_sas dm_mod [last unloaded: scsi_wait_scan]
Pid: 79910, comm: ls Tainted: G           ---------------- T 2.6.32-131.6.1.el6.x86_64 #1 PRIMERGY RX900 S1
RIP: 0010:[<ffffffff81192957>]  [<ffffffff81192957>] commit_tree+0x77/0x100
RSP: 0018:ffff885f1484dab8  EFLAGS: 00010246
RAX: ffff881f5f43d3e8 RBX: ffff885f1484dab8 RCX: ffff885f1484dab8
RDX: ffff881f5f43d3e8 RSI: ffff881f5f43d3e8 RDI: ffff885f1484dab8
RBP: ffff885f1484dae8 R08: ffff881f5f43d3e8 R09: 0000000000000000
R10: ffff882080440a40 R11: 0000000000000000 R12: 0000000000000000
R13: ffff881f5f43d380 R14: ffff881f5fcba2c0 R15: 0000000000000000
FS:  00007f9b188177a0(0000) GS:ffff88011c700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000018 CR3: 0000007fecaf5000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process ls (pid: 79910, threadinfo ffff885f1484c000, task ffff881fc4164b00)
Stack:
 ffff881f5f43d3e8 ffff881f5f43d3e8 ffff881f5f43d380 ffff885f1484db08
<0> ffff881f5fcba2c0 ffff885f1484ddd8 ffff885f1484db48 ffffffff81192c6f
<0> ffff881c94a4d200 000000001484dbf8 ffff885f1484db08 ffff885f1484db08
Call Trace:
 [<ffffffff81192c6f>] attach_recursive_mnt+0x28f/0x2a0
 [<ffffffff81192d80>] graft_tree+0x100/0x140
 [<ffffffff814dc686>] ? down_write+0x16/0x40
 [<ffffffff81192e5f>] do_add_mount+0x9f/0x160
 [<ffffffffa045ce2f>] nfs_follow_mountpoint+0x1bf/0x570 [nfs]
 [<ffffffff811810a0>] do_follow_link+0x120/0x440
 [<ffffffffa03112e0>] ? put_rpccred+0x50/0x150 [sunrpc]
 [<ffffffff81180eeb>] __link_path_walk+0x78b/0x820
 [<ffffffff8118164a>] path_walk+0x6a/0xe0
 [<ffffffff8118181b>] do_path_lookup+0x5b/0xa0
 [<ffffffff811819a7>] user_path_at+0x57/0xa0
 [<ffffffff81041594>] ? __do_page_fault+0x1e4/0x480
 [<ffffffff810ce97d>] ? audit_filter_rules+0x2d/0xa10
 [<ffffffff81177cac>] vfs_fstatat+0x3c/0x80
 [<ffffffff81177d5e>] vfs_lstat+0x1e/0x20
 [<ffffffff81177d84>] sys_newlstat+0x24/0x50
 [<ffffffff810d1ad2>] ? audit_syscall_entry+0x272/0x2a0
 [<ffffffff814e054e>] ? do_page_fault+0x3e/0xa0
 [<ffffffff8100b172>] system_call_fastpath+0x16/0x1b
Code: 83 e8 68 eb 12 0f 1f 80 00 00 00 00 4c 89 a0 c0 00 00 00 48 8d 42 98 48 8b 50 68 48 8d 48 68 48 39 cb 0f 18 0a 75 e5 48 8b 45 d0 <49> 8b 54 24 18 48 39 d8 74 15 48 8b 0a 48 8b 5d d8 48 89 50 08 
RIP  [<ffffffff81192957>] commit_tree+0x77/0x100
 RSP <ffff885f1484dab8>
CR2: 0000000000000018