Bug 1457921

(In reply to Steve Dickson from comment #0)
> For the NFS exports identified with the fsid=0 option which means it's the
> root of all exported filesystem, previously (rhel-7.3) we can only mount it
> with command "mount -t nfs4 server:/ /mnt/home", while command "mount -t
> nfs4 server:/home /mnt/home" gets failed.  The difference being
> "server:/home" and "server:/".
> 
> But now with the latest nfs-utils, command "mount -t nfs4 server:/home
> /mnt/home" successes and it actually mounts with NFS version 3.

Why is that a problem?

Sorry, I missed that you're mounting with "nfs4", so it should mount v4.x or fail, ok!

nfs-utils-2.1.1-5.rc3.fc25 has been submitted as an update to Fedora 25. https://bodhi.fedoraproject.org/updates/FEDORA-2017-5ce009e3bc

nfs-utils-2.1.1-5.rc3.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-8af6f7f786

nfs-utils-2.1.1-5.rc3.fc25 has been pushed to the Fedora 25 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-5ce009e3bc

nfs-utils-2.1.1-5.rc3.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-8af6f7f786

nfs-utils-2.1.1-5.rc3.fc25 has been pushed to the Fedora 25 stable repository. If problems still persist, please make note of it in this bug report.

nfs-utils-2.1.1-5.rc3.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.

Caused NFS to hang to the point we had to reboot.
nfs-utils x86_64 1:2.1.1-5.rc4.fc25

Jun 29 02:23:27 dsm rpc.idmapd: rpc.idmapd: conf_reinit: open ("(null)", O_RDONLY) failed
Jun 29 02:23:27 dsm rpc.idmapd: rpc.idmapd: conf_reinit: open ("(null)", O_RDONLY) failed
Jun 29 02:23:27 dsm kernel: nfsd: last server has exited, flushing export cache

Jun 29 02:23:27 dsm systemd: Starting NFS server and services...
Jun 29 02:23:27 dsm kernel: divide error: 0000 [#1] SMP
Jun 29 02:23:27 dsm kernel: Modules linked in: fuse arc4 md4 nls_utf8 cifs ccm rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache cfg80211 rfkill nf_log_ipv4 nf_log_common xt_LOG xt_limit xt_multiport ipt_MASQUERADE nf_nat_masquerade_ipv4 ip6t_REJECT nf_reject_ipv6 nf_con
ntrack_ipv6 iptable_nat nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_conntrack nf_nat nf_conntrack libcrc32c ip6table_filter ip6_tables iptable_mangle joydev coretemp kvm iTCO_wdt gpio_ich iTCO_vendor_support irqbypass ses ipmi_ssif enclosure dcdbas 
scsi_transport_sas i5000_edac ipmi_si edac_core lpc_ich ipmi_devintf i5k_amb ipmi_msghandler shpchp tpm_tis tpm_tis_core tpm nfsd auth_rpcgss nfs_acl lockd grace sunrpc binfmt_misc uas usb_storage amdkfd amd_iommu_v2 radeon i2c_algo_bit drm_kms_helper ttm drm ata_gene
ric pata_acpi serio_raw
Jun 29 02:23:27 dsm kernel: megaraid_sas bnx2
Jun 29 02:23:27 dsm kernel: CPU: 4 PID: 7781 Comm: rpc.nfsd Not tainted 4.11.5-200.fc25.x86_64 #1
Jun 29 02:23:27 dsm kernel: Hardware name: Dell Inc. PowerEdge 1950/0TT740, BIOS 2.2.6 02/05/2008
Jun 29 02:23:27 dsm kernel: task: ffff9290e5034880 task.stack: ffffa770ce0c4000
Jun 29 02:23:27 dsm kernel: RIP: 0010:svc_pool_for_cpu+0x2b/0x80 [sunrpc]
Jun 29 02:23:27 dsm kernel: RSP: 0018:ffffa770ce0c7c18 EFLAGS: 00010246
Jun 29 02:23:27 dsm kernel: RAX: 0000000000000000 RBX: ffff9290286a6000 RCX: 0000000000000002
Jun 29 02:23:27 dsm kernel: RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff928ec3d45500
Jun 29 02:23:27 dsm kernel: RBP: ffffa770ce0c7c18 R08: ffff928ec3d45528 R09: 0000000000018783
Jun 29 02:23:27 dsm kernel: R10: ffffffffc06fb100 R11: 0000000000000000 R12: ffff9290286a6010
Jun 29 02:23:27 dsm kernel: R13: ffff9290286a6018 R14: ffff928ec3d45528 R15: ffff928ec3d45500
Jun 29 02:23:27 dsm kernel: FS:  00007f0f69cacc40(0000) GS:ffff9290efd00000(0000) knlGS:0000000000000000
Jun 29 02:23:27 dsm kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Jun 29 02:23:27 dsm kernel: CR2: 00007ffede0fe0a8 CR3: 00000001fb7c4000 CR4: 00000000000006e0
Jun 29 02:23:27 dsm kernel: Call Trace:
Jun 29 02:23:27 dsm kernel: svc_xprt_do_enqueue+0xef/0x260 [sunrpc]
Jun 29 02:23:27 dsm kernel: svc_xprt_received+0x47/0x90 [sunrpc]
Jun 29 02:23:27 dsm kernel: svc_add_new_perm_xprt+0x76/0x90 [sunrpc]
Jun 29 02:23:27 dsm kernel: svc_addsock+0x14b/0x200 [sunrpc]
Jun 29 02:23:27 dsm kernel: ? recalc_sigpending+0x1b/0x50
Jun 29 02:23:27 dsm kernel: ? __getnstimeofday64+0x41/0xd0
Jun 29 02:23:27 dsm kernel: ? do_gettimeofday+0x29/0x90
Jun 29 02:23:27 dsm kernel: write_ports+0x255/0x2c0 [nfsd]
Jun 29 02:23:27 dsm kernel: ? _copy_from_user+0x4e/0x80
Jun 29 02:23:27 dsm kernel: ? write_recoverydir+0x100/0x100 [nfsd]
Jun 29 02:23:27 dsm kernel: nfsctl_transaction_write+0x48/0x80 [nfsd]
Jun 29 02:23:27 dsm kernel: __vfs_write+0x37/0x160
Jun 29 02:23:27 dsm kernel: ? __inet_hash+0xd2/0x260
Jun 29 02:23:27 dsm kernel: vfs_write+0xb5/0x1a0
Jun 29 02:23:27 dsm kernel: SyS_write+0x55/0xc0
Jun 29 02:23:27 dsm kernel: entry_SYSCALL_64_fastpath+0x1a/0xa9
Jun 29 02:23:27 dsm kernel: RIP: 0033:0x7f0f695c8ae0
Jun 29 02:23:27 dsm kernel: RSP: 002b:00007ffede056ba8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
Jun 29 02:23:27 dsm kernel: RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f0f695c8ae0
Jun 29 02:23:27 dsm kernel: RDX: 0000000000000002 RSI: 00005637ab1dd600 RDI: 0000000000000003
Jun 29 02:23:27 dsm kernel: RBP: 00007ffede056ba0 R08: 0000000000000001 R09: 0000000000000002
Jun 29 02:23:27 dsm kernel: R10: 0000000000000064 R11: 0000000000000246 R12: 0000000000000004
Jun 29 02:23:27 dsm kernel: R13: 00005637abfa37a0 R14: 00005637abfa3720 R15: 00007ffede056658
Jun 29 02:23:27 dsm kernel: Code: 66 66 66 66 90 48 8b 87 98 00 00 00 55 48 89 e5 48 83 78 08 00 74 10 8b 05 97 51 02 00 83 f8 01 74 40 83 f8 02 74 19 31 c0 31 d2 <f7> b7 88 00 00 00 5d 89 d0 48 c1 e0 07 48 03 87 90 00 00 00 c3 
Jun 29 02:23:27 dsm kernel: RIP: svc_pool_for_cpu+0x2b/0x80 [sunrpc] RSP: ffffa770ce0c7c18
Jun 29 02:23:27 dsm kernel: ---[ end trace 7a2bfc4aacf7a21e ]---

(In reply to RobbieTheK from comment #9)
> Caused NFS to hang to the point we had to reboot.
> nfs-utils x86_64 1:2.1.1-5.rc4.fc25
> 
> Jun 29 02:23:27 dsm rpc.idmapd: rpc.idmapd: conf_reinit: open ("(null)",
> O_RDONLY) failed
> Jun 29 02:23:27 dsm rpc.idmapd: rpc.idmapd: conf_reinit: open ("(null)",
> O_RDONLY) failed
> Jun 29 02:23:27 dsm kernel: nfsd: last server has exited, flushing export
> cache
> 
The bug fix for this mounting bug did not cause this problem. 
So please open up another bz about this problem.