linux-kernel - [Question] A panic when reboot --force the system

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Date:	Fri, 23 Oct 2015 17:45:57 +0800
From:	Rui Xiang <rui.xiang@...wei.com>
To:	<sysvinit-devel@...gnu.org>, <systemd-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>
CC:	Miao Xie <miaoxie@...wei.com>, Xishi Qiu <qiuxishi@...wei.com>
Subject: [Question] A panic when reboot --force the system

Hi，list

I encounter a panic about init process.

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.

In our host, kswapd would be wake up while using a lot of memory, and then reclaim
some pages from init process. If we execute *"reboot"* or *"reboot -f"* to reboot
host through sysvinit, reboot process will call sys_reboot and shut down the sas
driver(disk), then will trigger the panic of init process.

As follow,

		HOST					reboot process			init process
use a lot of memory
 wake up kswapd
   reclaim some pages
   (these pages are code segment
	or data segment of init process)
   from init thread (pid=1)
								reboot
								  sys_reboot
									shutdown disk driver
														init thread read data from disk
														  page_fault
															filemap_fault
															  readpage failed because the disk is closed
															return VM_FAULT_SIGBUS
															send signal SIGBUS
														  do_signal
															do_exit
															trigger the panic

It seems that reboot or force reboot through *sysvinit* have the problem.
Furthermore, using reboot -f in *systemd* should also have this problem, right?

And is that a bug for current reboot process in sysvinit or systemd?

All comments are welcome, thanks.

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