What killed init in "Kernel panic - not syncing: Attempted to kill init!"

Issue

Signals delivered to init causing it to die (SIGKILL, SIGTERM, SIGBUS, ... depending on signal handler action for a given signal) lead to kernel panics with following messages in the message buffer:

Kernel panic - not syncing: Attempted to kill init!
Pid: 1, comm: init Tainted: P           ---------------    2.6.32-504.el6.x86_64 #1
Call Trace:
 [<ffffffff815292bc>] ? panic+0xa7/0x16f
 [<ffffffff8132f3d6>] ? get_current_tty+0x66/0x70
 [<ffffffff8107a5f2>] ? do_exit+0x862/0x870
 [<ffffffff8108c51d>] ? __sigqueue_free+0x3d/0x50
 [<ffffffff8107a658>] ? do_group_exit+0x58/0xd0
 [<ffffffff81090306>] ? get_signal_to_deliver+0x1f6/0x460
 [<ffffffff8100a265>] ? do_signal+0x75/0x800
 [<ffffffff8109eefc>] ? remove_wait_queue+0x3c/0x50
 [<ffffffff81010000>] ? show_registers+0x160/0x280
 [<ffffffff8104c527>] ? is_prefetch+0xb7/0x230
 [<ffffffff810796c8>] ? sys_waitid+0xa8/0x1f0
 [<ffffffff8100aa80>] ? do_notify_resume+0x90/0xc0
 [<ffffffff8100badc>] ? retint_signal+0x48/0x8c