You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
441 lines
16 KiB
441 lines
16 KiB
<?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> |
|
<listitem><para>debug_object_assert_init</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> |
|
|
|
<sect1 id="debug_object_assert_init"> |
|
<title>debug_object_assert_init</title> |
|
<para> |
|
This function is called to assert that an object has been |
|
initialized. |
|
</para> |
|
<para> |
|
When the real object is not tracked by debugobjects, it calls |
|
fixup_assert_init of the object type description structure |
|
provided by the caller, with the hardcoded object state |
|
ODEBUG_NOT_AVAILABLE. The fixup function can correct the problem |
|
by calling debug_object_init and other specific initializing |
|
functions. |
|
</para> |
|
<para> |
|
When the real object is already tracked by debugobjects it is |
|
ignored. |
|
</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> |
|
<sect1 id="fixup_assert_init"> |
|
<title>fixup_assert_init</title> |
|
<para> |
|
This function is called from the debug code whenever a problem |
|
in debug_object_assert_init is detected. |
|
</para> |
|
<para> |
|
Called from debug_object_assert_init() with a hardcoded state |
|
ODEBUG_STATE_NOTAVAILABLE when the object is not found in the |
|
debug bucket. |
|
</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, this function should make sure debug_object_init() is |
|
called before returning. |
|
</para> |
|
<para> |
|
The handling of statically initialized objects is a special |
|
case. The fixup function should check if this is a legitimate |
|
case of a statically initialized object or not. In this case only |
|
debug_object_init() should be called to make the object known to |
|
the tracker. Then the function should return 0 because this is not |
|
a real fixup. |
|
</para> |
|
</sect1> |
|
</chapter> |
|
<chapter id="bugs"> |
|
<title>Known Bugs And Assumptions</title> |
|
<para> |
|
None (knock on wood). |
|
</para> |
|
</chapter> |
|
</book>
|
|
|