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