[RFC] panic when reboot the system

[Xishi Qiu <qiuxishi@huawei.com>]

Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000007

Pid: 1, comm: init Tainted: G  R        O 3.4.24.19-0.11-default #1
Call Trace:
 [<ffffffff8144dd24>] panic+0xc1/0x1e2
 [<ffffffff8104483b>] do_exit+0x7db/0x8d0
 [<ffffffff81044c7a>] do_group_exit+0x3a/0xa0
 [<ffffffff8105394b>] get_signal_to_deliver+0x1ab/0x5e0
 [<ffffffff81002270>] do_signal+0x60/0x5f0
 [<ffffffff8145bf97>] ? do_page_fault+0x4a7/0x4d0
 [<ffffffff81170d2c>] ? poll_select_copy_remaining+0xec/0x140
 [<ffffffff81002885>] do_notify_resume+0x65/0x80
 [<ffffffff8124ca7e>] ? trace_hardirqs_on_thunk+0x3a/0x3c
 [<ffffffff814587ab>] retint_signal+0x4d/0x92


The system has a little memory left, then reboot it, and get the panic.
Perhaps this is a bug and trigger it like this and the latest kernel maybe
also have the problem.

use a lot of memory
  wake up kswapd()
    reclaim some pages from init thread (pid=1)
      reboot
        shutdown the disk
          init thread read data from disk
            page fault, because the page has already reclaimed
              receive SIGBUS, and init thread exit
                trigger the panic


Thanks,
Xishi Qiu

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