Server hung with message INFO: task sshd:18846 blocked for more than 120 seconds.

Issue

• Server hung with following messages in /var/log/messages.

kernel: INFO: task sshd:18846 blocked for more than 120 seconds.
kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kernel: sshd          D 0000000000000000     0 18846  16401 0x00000080
kernel: ffff8800ab0c1768 0000000000000082 0000000000000000 ffff8800ab0c1758
kernel: 00000000000024e0 ffff8803e416eea8 0000000000000002 ffff8800ab0c18c0
kernel: ffff88042f165ab8 ffff8800ab0c1fd8 000000000000f4e8 ffff88042f165ab8
kernel: Call Trace:
kernel: [<ffffffff814ed975>] schedule_timeout+0x215/0x2e0
kernel: [<ffffffff814ed5f3>] wait_for_common+0x123/0x180
kernel: [<ffffffff8105e7f0>] ? default_wake_function+0x0/0x20
kernel: [<ffffffff814ed70d>] wait_for_completion+0x1d/0x20
kernel: [<ffffffff8108bb67>] flush_work+0x77/0xc0
kernel: [<ffffffff8108b5d0>] ? wq_barrier_func+0x0/0x20
kernel: [<ffffffff8108bd84>] flush_delayed_work+0x54/0x70
kernel: [<ffffffff81314d25>] tty_flush_to_ldisc+0x15/0x20
kernel: [<ffffffff8130f867>] n_tty_poll+0x67/0x1d0
kernel: [<ffffffff8130b33a>] tty_poll+0x8a/0xa0
kernel: [<ffffffff8118b692>] do_select+0x392/0x6b0
kernel: [<ffffffff8118b9b0>] ? __pollwait+0x0/0xf0
kernel: [<ffffffff8118baa0>] ? pollwake+0x0/0x60
kernel: [<ffffffff8118baa0>] ? pollwake+0x0/0x60
kernel: [<ffffffff8118baa0>] ? pollwake+0x0/0x60
kernel: [<ffffffff8118baa0>] ? pollwake+0x0/0x60
kernel: [<ffffffff814ef5cb>] ? _spin_unlock_bh+0x1b/0x20
kernel: [<ffffffff8141cdee>] ? release_sock+0xce/0xe0
kernel: [<ffffffff8146fc5c>] ? tcp_sendmsg+0x73c/0xa10
kernel: [<ffffffff8141be5e>] ? sock_aio_write+0x15e/0x170
kernel: [<ffffffff8118c49a>] core_sys_select+0x18a/0x2c0
kernel: [<ffffffff81090a90>] ? autoremove_wake_function+0x0/0x40
kernel: [<ffffffff81218dff>] ? selinux_file_permission+0xbf/0x150
kernel: [<ffffffff8118c827>] sys_select+0x47/0x110
kernel: [<ffffffff8100b0f2>] system_call_fastpath+0x16/0x1b