NFSv3 server ignores freeze status of backing filesystem

Issue

Example backtraces in logs:

Jun  2 23:01:08 sapcs1 kernel: ------------[ cut here ]------------
Jun  2 23:01:08 sapcs1 kernel: WARNING: at fs/ext4/super.c:240 ext4_journal_start_sb+0xce/0xe0 [ext4]() (Not tainted)
Jun  2 23:01:08 sapcs1 kernel: Hardware name: VMware Virtual Platform
Jun  2 23:01:08 sapcs1 kernel: Modules linked in: bridge nfsd exportfs autofs4 nfs lockd fscache auth_rpcgss nfs_acl sunrpc 8021q garp stp llc ipv6 vsock(U) uinput ppdev parport_pc parport sg microcode vmware_balloon vmci(U) i2c_piix4 i2c_core shpchp ext4 mbcache jbd2 sd_mod crc_t10dif sr_mod cdrom vmxnet3 vmw_pvscsi pata_acpi ata_generic ata_piix dm_mirror dm_region_hash dm_log dm_mod [last unloaded: speedstep_lib]
Jun  2 23:01:08 sapcs1 kernel: Pid: 2745, comm: nfsd Not tainted 2.6.32-358.14.1.el6.x86_64 #1
Jun  2 23:01:08 sapcs1 kernel: Call Trace:
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff8106e307>] ? warn_slowpath_common+0x87/0xc0
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff8106e35a>] ? warn_slowpath_null+0x1a/0x20
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa00c62de>] ? ext4_journal_start_sb+0xce/0xe0 [ext4]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa00b1c20>] ? ext4_setattr+0x1d0/0x330 [ext4]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff8119e7a8>] ? notify_change+0x168/0x340
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa038d80c>] ? nfsd_setattr+0x32c/0x3e0 [nfsd]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa0396d16>] ? nfsd3_proc_setattr+0x76/0xc0 [nfsd]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa038843e>] ? nfsd_dispatch+0xfe/0x240 [nfsd]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa0269614>] ? svc_process_common+0x344/0x640 [sunrpc]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff81063330>] ? default_wake_function+0x0/0x20
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa0269c50>] ? svc_process+0x110/0x160 [sunrpc]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa0388b62>] ? nfsd+0xc2/0x160 [nfsd]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffffa0388aa0>] ? nfsd+0x0/0x160 [nfsd]
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff81096956>] ? kthread+0x96/0xa0
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff8100c0ca>] ? child_rip+0xa/0x20
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff810968c0>] ? kthread+0x0/0xa0
Jun  2 23:01:08 sapcs1 kernel: [<ffffffff8100c0c0>] ? child_rip+0x0/0x20
Jun  2 23:01:08 sapcs1 kernel: ---[ end trace 205b0b9eafa198cb ]---