<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> <book id="debug-objects-guide"> <bookinfo>  <title>Debug objects life time</title>   <authorgroup>   <author>    <firstname>Thomas</firstname>    <surname>Gleixner</surname>    <affiliation>     <address>      <email>tglx@linutronix.de</email>     </address>    </affiliation>   </author>  </authorgroup>   <copyright>   <year>2008</year>   <holder>Thomas Gleixner</holder>  </copyright>   <legalnotice>   <para>     This documentation is free software; you can redistribute     it and/or modify it under the terms of the GNU General Public     License version 2 as published by the Free Software Foundation.   </para>    <para>     This program is distributed in the hope that it will be     useful, but WITHOUT ANY WARRANTY; without even the implied     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.     See the GNU General Public License for more details.   </para>    <para>     You should have received a copy of the GNU General Public     License along with this program; if not, write to the Free     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,     MA 02111-1307 USA   </para>    <para>     For more details see the file COPYING in the source     distribution of Linux.   </para>  </legalnotice> </bookinfo> <toc></toc>   <chapter id="intro">    <title>Introduction</title>    <para>      debugobjects is a generic infrastructure to track the life time      of kernel objects and validate the operations on those.    </para>    <para>      debugobjects is useful to check for the following error patterns:	<itemizedlist>	  <listitem><para>Activation of uninitialized objects</para></listitem>	  <listitem><para>Initialization of active objects</para></listitem>	  <listitem><para>Usage of freed/destroyed objects</para></listitem>	</itemizedlist>    </para>    <para>      debugobjects is not changing the data structure of the real      object so it can be compiled in with a minimal runtime impact      and enabled on demand with a kernel command line option.    </para>  </chapter>   <chapter id="howto">    <title>Howto use debugobjects</title>    <para>      A kernel subsystem needs to provide a data structure which      describes the object type and add calls into the debug code at      appropriate places. The data structure to describe the object      type needs at minimum the name of the object type. Optional      functions can and should be provided to fixup detected problems      so the kernel can continue to work and the debug information can      be retrieved from a live system instead of hard core debugging      with serial consoles and stack trace transcripts from the      monitor.    </para>    <para>      The debug calls provided by debugobjects are:      <itemizedlist>	<listitem><para>debug_object_init</para></listitem>	<listitem><para>debug_object_init_on_stack</para></listitem>	<listitem><para>debug_object_activate</para></listitem>	<listitem><para>debug_object_deactivate</para></listitem>	<listitem><para>debug_object_destroy</para></listitem>	<listitem><para>debug_object_free</para></listitem>      </itemizedlist>      Each of these functions takes the address of the real object and      a pointer to the object type specific debug description      structure.    </para>    <para>      Each detected error is reported in the statistics and a limited      number of errors are printk'ed including a full stack trace.    </para>    <para>      The statistics are available via /sys/kernel/debug/debug_objects/stats.      They provide information about the number of warnings and the      number of successful fixups along with information about the      usage of the internal tracking objects and the state of the      internal tracking objects pool.    </para>  </chapter>  <chapter id="debugfunctions">    <title>Debug functions</title>    <sect1 id="prototypes">      <title>Debug object function reference</title>!Elib/debugobjects.c    </sect1>    <sect1 id="debug_object_init">      <title>debug_object_init</title>      <para>	This function is called whenever the initialization function	of a real object is called.      </para>      <para>	When the real object is already tracked by debugobjects it is	checked, whether the object can be initialized.  Initializing	is not allowed for active and destroyed objects. When	debugobjects detects an error, then it calls the fixup_init	function of the object type description structure if provided	by the caller. The fixup function can correct the problem	before the real initialization of the object happens. E.g. it	can deactivate an active object in order to prevent damage to	the subsystem.      </para>      <para>	When the real object is not yet tracked by debugobjects,	debugobjects allocates a tracker object for the real object	and sets the tracker object state to ODEBUG_STATE_INIT. It	verifies that the object is not on the callers stack. If it is	on the callers stack then a limited number of warnings	including a full stack trace is printk'ed. The calling code	must use debug_object_init_on_stack() and remove the object	before leaving the function which allocated it. See next	section.      </para>    </sect1>     <sect1 id="debug_object_init_on_stack">      <title>debug_object_init_on_stack</title>      <para>	This function is called whenever the initialization function	of a real object which resides on the stack is called.      </para>      <para>	When the real object is already tracked by debugobjects it is	checked, whether the object can be initialized. Initializing	is not allowed for active and destroyed objects. When	debugobjects detects an error, then it calls the fixup_init	function of the object type description structure if provided	by the caller. The fixup function can correct the problem	before the real initialization of the object happens. E.g. it	can deactivate an active object in order to prevent damage to	the subsystem.      </para>      <para>	When the real object is not yet tracked by debugobjects	debugobjects allocates a tracker object for the real object	and sets the tracker object state to ODEBUG_STATE_INIT. It	verifies that the object is on the callers stack.      </para>      <para>	An object which is on the stack must be removed from the	tracker by calling debug_object_free() before the function	which allocates the object returns. Otherwise we keep track of	stale objects.      </para>    </sect1>     <sect1 id="debug_object_activate">      <title>debug_object_activate</title>      <para>	This function is called whenever the activation function of a	real object is called.      </para>      <para>	When the real object is already tracked by debugobjects it is	checked, whether the object can be activated.  Activating is	not allowed for active and destroyed objects. When	debugobjects detects an error, then it calls the	fixup_activate function of the object type description	structure if provided by the caller. The fixup function can	correct the problem before the real activation of the object	happens. E.g. it can deactivate an active object in order to	prevent damage to the subsystem.      </para>      <para>	When the real object is not yet tracked by debugobjects then	the fixup_activate function is called if available. This is	necessary to allow the legitimate activation of statically	allocated and initialized objects. The fixup function checks	whether the object is valid and calls the debug_objects_init()	function to initialize the tracking of this object.      </para>      <para>	When the activation is legitimate, then the state of the	associated tracker object is set to ODEBUG_STATE_ACTIVE.      </para>    </sect1>     <sect1 id="debug_object_deactivate">      <title>debug_object_deactivate</title>      <para>	This function is called whenever the deactivation function of	a real object is called.      </para>      <para>	When the real object is tracked by debugobjects it is checked,	whether the object can be deactivated. Deactivating is not	allowed for untracked or destroyed objects.      </para>      <para>	When the deactivation is legitimate, then the state of the	associated tracker object is set to ODEBUG_STATE_INACTIVE.      </para>    </sect1>     <sect1 id="debug_object_destroy">      <title>debug_object_destroy</title>      <para>	This function is called to mark an object destroyed. This is	useful to prevent the usage of invalid objects, which are	still available in memory: either statically allocated objects	or objects which are freed later.      </para>      <para>	When the real object is tracked by debugobjects it is checked,	whether the object can be destroyed. Destruction is not	allowed for active and destroyed objects. When debugobjects	detects an error, then it calls the fixup_destroy function of	the object type description structure if provided by the	caller. The fixup function can correct the problem before the	real destruction of the object happens. E.g. it can deactivate	an active object in order to prevent damage to the subsystem.      </para>      <para>	When the destruction is legitimate, then the state of the	associated tracker object is set to ODEBUG_STATE_DESTROYED.      </para>    </sect1>     <sect1 id="debug_object_free">      <title>debug_object_free</title>      <para>	This function is called before an object is freed.      </para>      <para>	When the real object is tracked by debugobjects it is checked,	whether the object can be freed. Free is not allowed for	active objects. When debugobjects detects an error, then it	calls the fixup_free function of the object type description	structure if provided by the caller. The fixup function can	correct the problem before the real free of the object	happens. E.g. it can deactivate an active object in order to	prevent damage to the subsystem.      </para>      <para>	Note that debug_object_free removes the object from the	tracker. Later usage of the object is detected by the other	debug checks.      </para>    </sect1>  </chapter>  <chapter id="fixupfunctions">    <title>Fixup functions</title>    <sect1 id="debug_obj_descr">      <title>Debug object type description structure</title>!Iinclude/linux/debugobjects.h    </sect1>    <sect1 id="fixup_init">      <title>fixup_init</title>      <para>	This function is called from the debug code whenever a problem	in debug_object_init is detected. The function takes the	address of the object and the state which is currently	recorded in the tracker.      </para>      <para>	Called from debug_object_init when the object state is:	<itemizedlist>	  <listitem><para>ODEBUG_STATE_ACTIVE</para></listitem>	</itemizedlist>      </para>      <para>	The function returns 1 when the fixup was successful,	otherwise 0. The return value is used to update the	statistics.      </para>      <para>	Note, that the function needs to call the debug_object_init()	function again, after the damage has been repaired in order to	keep the state consistent.      </para>    </sect1>     <sect1 id="fixup_activate">      <title>fixup_activate</title>      <para>	This function is called from the debug code whenever a problem	in debug_object_activate is detected.      </para>      <para>	Called from debug_object_activate when the object state is:	<itemizedlist>	  <listitem><para>ODEBUG_STATE_NOTAVAILABLE</para></listitem>	  <listitem><para>ODEBUG_STATE_ACTIVE</para></listitem>	</itemizedlist>      </para>      <para>	The function returns 1 when the fixup was successful,	otherwise 0. The return value is used to update the	statistics.      </para>      <para>	Note that the function needs to call the debug_object_activate()	function again after the damage has been repaired in order to	keep the state consistent.      </para>      <para>	The activation of statically initialized objects is a special	case. When debug_object_activate() has no tracked object for	this object address then fixup_activate() is called with	object state ODEBUG_STATE_NOTAVAILABLE. The fixup function	needs to check whether this is a legitimate case of a	statically initialized object or not. In case it is it calls	debug_object_init() and debug_object_activate() to make the	object known to the tracker and marked active. In this case	the function should return 0 because this is not a real fixup.      </para>    </sect1>     <sect1 id="fixup_destroy">      <title>fixup_destroy</title>      <para>	This function is called from the debug code whenever a problem	in debug_object_destroy is detected.      </para>      <para>	Called from debug_object_destroy when the object state is:	<itemizedlist>	  <listitem><para>ODEBUG_STATE_ACTIVE</para></listitem>	</itemizedlist>      </para>      <para>	The function returns 1 when the fixup was successful,	otherwise 0. The return value is used to update the	statistics.      </para>    </sect1>    <sect1 id="fixup_free">      <title>fixup_free</title>      <para>	This function is called from the debug code whenever a problem	in debug_object_free is detected. Further it can be called	from the debug checks in kfree/vfree, when an active object is	detected from the debug_check_no_obj_freed() sanity checks.      </para>      <para>	Called from debug_object_free() or debug_check_no_obj_freed()	when the object state is:	<itemizedlist>	  <listitem><para>ODEBUG_STATE_ACTIVE</para></listitem>	</itemizedlist>      </para>      <para>	The function returns 1 when the fixup was successful,	otherwise 0. The return value is used to update the	statistics.      </para>    </sect1>  </chapter>  <chapter id="bugs">    <title>Known Bugs And Assumptions</title>    <para>	None (knock on wood).    </para>  </chapter></book>