kgdb,debug_core: add the ability to control the reboot notifier

Sometimes it is desirable to stop the kernel debugger before allowing
a system to reboot either with kdb or kgdb.  This patch adds the
ability to turn the reboot notifier on and off or enter the debugger
and stop kernel execution before rebooting.

It is possible to change the setting after booting the kernel with the
following:

echo 1 > /sys/module/debug_core/parameters/kgdbreboot

It is also possible to change this setting using kdb / kgdb to
manipulate the variable directly.

Using KDB:
   mm kgdbreboot 1

Using gdb:
   set kgdbreboot=1

Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl
index d71b57fcf116..4ee4ba3509fc 100644
--- a/Documentation/DocBook/kgdb.tmpl
+++ b/Documentation/DocBook/kgdb.tmpl
@@ -362,6 +362,23 @@
    </para>
   </para>
   </sect1>
+   <sect1 id="kgdbreboot">
+   <title>Run time parameter: kgdbreboot</title>
+   <para> The kgdbreboot feature allows you to change how the debugger
+   deals with the reboot notification.  You have 3 choices for the
+   behavior.  The default behavior is always set to 0.</para>
+   <orderedlist>
+   <listitem><para>echo -1 > /sys/module/debug_core/parameters/kgdbreboot</para>
+   <para>Ignore the reboot notification entirely.</para>
+   </listitem>
+   <listitem><para>echo 0 > /sys/module/debug_core/parameters/kgdbreboot</para>
+   <para>Send the detach message to any attached debugger client.</para>
+   </listitem>
+   <listitem><para>echo 1 > /sys/module/debug_core/parameters/kgdbreboot</para>
+   <para>Enter the debugger on reboot notify.</para>
+   </listitem>
+   </orderedlist>
+  </sect1>
   </chapter>
   <chapter id="usingKDB">
   <title>Using kdb</title>