Why does a significant delay or a hang occur during Red Hat Enterprise Linux 7 installation with NFS repository?

Issue

• Trying to install Red Hat Enterprise Linux 7 with NFS repository and PXE boot. It's automated with kickstart.
• The problem observed is during the installation, the main window will sit at "Starting installer, one moment..." for about 20 minutes. And, it sometimes continues after that, or keeps getting hang.
• When the problem happens, it's not possible to enter a background shell with Ctrl-Alt-F2.
• The following tracebacks were output in some cases.

02:34:53,340 NOTICE kernel:[  572.445600] nfs: server 192.168.0.254 not responding, still trying
02:35:25,368 ERR kernel:[  604.498643] INFO: task loop0:1239 blocked for more than 120 seconds.
02:35:25,368 ERR kernel:[  604.498647] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
02:35:25,368 INFO kernel:[  604.498651] loop0           D ffff88013fc13680     0  1239      2 0x00000000
02:35:25,368 WARNING kernel:[  604.498664]  ffff8800ba50b998 0000000000000046 ffff880130d9cfa0 ffff8800ba50bfd8
02:35:25,368 WARNING kernel:[  604.498668]  ffff8800ba50bfd8 ffff8800ba50bfd8 ffff880130d9cfa0 ffff88013fc13f48
02:35:25,368 WARNING kernel:[  604.498670]  ffff8800ba50ba20 0000000000000002 ffffffff81155f10 ffff8800ba50ba10
02:35:25,368 WARNING kernel:[  604.498673] Call Trace:
02:35:25,368 WARNING kernel:[  604.498694]  [<ffffffff81155f10>] ? wait_on_page_read+0x60/0x60
02:35:25,368 WARNING kernel:[  604.498698]  [<ffffffff8160955d>] io_schedule+0x9d/0x130
02:35:25,368 WARNING kernel:[  604.498700]  [<ffffffff81155f1e>] sleep_on_page+0xe/0x20
02:35:25,368 WARNING kernel:[  604.498702]  [<ffffffff8160746b>] __wait_on_bit_lock+0x5b/0xc0
02:35:25,368 WARNING kernel:[  604.498704]  [<ffffffff81156038>] __lock_page+0x78/0xa0
02:35:25,368 WARNING kernel:[  604.498707]  [<ffffffff81098270>] ? autoremove_wake_function+0x40/0x40
02:35:25,368 WARNING kernel:[  604.498709]  [<ffffffff8115625e>] ? find_get_page+0xe/0x20
02:35:25,368 WARNING kernel:[  604.498713]  [<ffffffff811f518a>] __generic_file_splice_read+0x5ca/0x5e0
02:35:25,368 WARNING kernel:[  604.498716]  [<ffffffff811f39f0>] ? page_cache_pipe_buf_release+0x20/0x20
02:35:25,368 WARNING kernel:[  604.498718]  [<ffffffff811ab69a>] ? kmem_cache_alloc+0x1ba/0x1d0
02:35:25,368 WARNING kernel:[  604.498721]  [<ffffffff812d4275>] ? cpumask_next_and+0x35/0x50
02:35:25,368 WARNING kernel:[  604.498724]  [<ffffffff810b51c4>] ? find_busiest_group+0x114/0x910
02:35:25,368 WARNING kernel:[  604.498726]  [<ffffffff810b1c4c>] ? update_curr+0xcc/0x150
02:35:25,368 WARNING kernel:[  604.498729]  [<ffffffff810ad7b8>] ? __enqueue_entity+0x78/0x80
02:35:25,368 WARNING kernel:[  604.498732]  [<ffffffff8126ee9a>] ? inode_has_perm.isra.33.constprop.62+0x2a/0x30
02:35:25,368 WARNING kernel:[  604.498734]  [<ffffffff811f51de>] generic_file_splice_read+0x3e/0x80
02:35:25,368 WARNING kernel:[  604.498762]  [<ffffffffa03657a5>] nfs_file_splice_read+0x75/0xc0 [nfs]
02:35:25,368 WARNING kernel:[  604.498765]  [<ffffffff811f4012>] do_splice_to+0x72/0x90
02:35:25,368 WARNING kernel:[  604.498767]  [<ffffffff811f40e7>] splice_direct_to_actor+0xb7/0x200
02:35:25,368 WARNING kernel:[  604.498770]  [<ffffffffa041dcd0>] ? do_bio_filebacked+0x320/0x320 [loop]
02:35:25,368 WARNING kernel:[  604.498772]  [<ffffffffa041dad1>] do_bio_filebacked+0x121/0x320 [loop]
02:35:25,368 WARNING kernel:[  604.498775]  [<ffffffffa041e43c>] loop_thread+0xfc/0x300 [loop]
02:35:25,368 WARNING kernel:[  604.498777]  [<ffffffff81098230>] ? wake_up_bit+0x30/0x30
02:35:25,368 WARNING kernel:[  604.498779]  [<ffffffffa041e340>] ? loop_attr_do_show_backing_file+0xe0/0xe0 [loop]
02:35:25,368 WARNING kernel:[  604.498781]  [<ffffffff8109726f>] kthread+0xcf/0xe0
02:35:25,368 WARNING kernel:[  604.498783]  [<ffffffff810971a0>] ? kthread_create_on_node+0x140/0x140
02:35:25,368 WARNING kernel:[  604.498786]  [<ffffffff81613cfc>] ret_from_fork+0x7c/0xb0
02:35:25,368 WARNING kernel:[  604.498787]  [<ffffffff810971a0>] ? kthread_create_on_node+0x140/0x140