444 lines
16 KiB
Cheetah
444 lines
16 KiB
Cheetah
|
<?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 true when the fixup was successful,
|
||
|
|
otherwise false. 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 true when the fixup was successful,
|
||
|
|
otherwise false. 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 false 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 true when the fixup was successful,
|
||
|
|
otherwise false. 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 true when the fixup was successful,
|
||
|
|
otherwise false. 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 true when the fixup was successful,
|
||
|
|
otherwise false. 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 false 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>
|