Why RHEL 6.4 machine crashes while trying to read from a tty in n_tty_read ?

Issue

Systems crashed due to upgrade from RHEL 6.2 to RHEL 6.4 with the following backtrace :

[848346.503219] kernel BUG at drivers/char/n_tty.c:1713!
[848346.508963] invalid opcode: 0000 [#1] SMP 
[848346.513765] last sysfs file: /sys/devices/pci0000:c0/0000:c0:05.2/class
[848346.521346] CPU 4 
...
[848346.559481] 
[848346.561342] Pid: 21051, comm: ssh Not tainted 2.6.32-358.11.1.el6.x86_64 #1 IBM System x3750 M4 -[8722AC1]-/00D1471
[848346.573346] RIP: 0010:[<ffffffff81329a27>]  [<ffffffff81329a27>] n_tty_read+0x987/0x990
[848346.582605] RSP: 0018:ffff8801797dbd88  EFLAGS: 00010246
[848346.588738] RAX: ffff880ecb9a9500 RBX: ffff881036ab2680 RCX: ffff88103a57e0d8
[848346.597004] RDX: ffff88103a57e1c0 RSI: ffff881036ab2680 RDI: ffff88103a57e000
[848346.605270] RBP: ffff8801797dbe98 R08: ffffffff81323f30 R09: 0101010101010101
[848346.613536] R10: 0000000000000000 R11: 0000000000000246 R12: ffff88103a57e000
[848346.621803] R13: ffff881069999298 R14: ffff88103a57e268 R15: ffff88103a57e51c
[848346.630072] FS:  00007f0e467217c0(0000) GS:ffff880028300000(0000) knlGS:0000000000000000
[848346.639406] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[848346.646025] CR2: 00007fb8c85ca000 CR3: 00000002acedf000 CR4: 00000000000407a0
[848346.654290] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[848346.662557] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[848346.670826] Process ssh (pid: 21051, threadinfo ffff8801797da000, task ffff880ecb9a9500)
[848346.682081] Stack:
[848346.684521]  ffffffff8100bb8e ffff8801797dbe18 ffff88103a57e1c8 ffff880ecb9a9500
[848346.692833] <d> ffff88103a57e1c0 ffff88103a57e490 0000000000000246 ffff880ecb9a9500
[848346.701754] <d> ffff88103a57e0d8 0000000000000000 ffff880ecb9a9500 ffffffffffffff10
[848346.710975] Call Trace:
[848346.713903]  [<ffffffff8100bb8e>] ? apic_timer_interrupt+0xe/0x20
[848346.720910]  [<ffffffff81510547>] ? _spin_unlock_irqrestore+0x17/0x20
[848346.728310]  [<ffffffff81063310>] ? default_wake_function+0x0/0x20
[848346.735453]  [<ffffffff81323fd6>] tty_read+0xa6/0xf0
[848346.741199]  [<ffffffff81181805>] vfs_read+0xb5/0x1a0
[848346.747042]  [<ffffffff81181941>] sys_read+0x51/0x90
[848346.752787]  [<ffffffff810dc595>] ? __audit_syscall_exit+0x265/0x290
[848346.760091]  [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b