mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-24 00:30:52 +07:00
8da3dc5334
Add the appropriate markup to get the kerneldoc comments out of lib/debugobjects.c that have never seen the light of day until now. A logical next step, left for the reader at the moment, is to move the function descriptions *out* of debug-objects.rst and into the kerneldoc comments themselves. Signed-off-by: Jonathan Corbet <corbet@lwn.net>
311 lines
11 KiB
ReStructuredText
311 lines
11 KiB
ReStructuredText
============================================
|
|
The object-lifetime debugging infrastructure
|
|
============================================
|
|
|
|
:Author: Thomas Gleixner
|
|
|
|
Introduction
|
|
============
|
|
|
|
debugobjects is a generic infrastructure to track the life time of
|
|
kernel objects and validate the operations on those.
|
|
|
|
debugobjects is useful to check for the following error patterns:
|
|
|
|
- Activation of uninitialized objects
|
|
|
|
- Initialization of active objects
|
|
|
|
- Usage of freed/destroyed objects
|
|
|
|
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.
|
|
|
|
Howto use debugobjects
|
|
======================
|
|
|
|
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.
|
|
|
|
The debug calls provided by debugobjects are:
|
|
|
|
- debug_object_init
|
|
|
|
- debug_object_init_on_stack
|
|
|
|
- debug_object_activate
|
|
|
|
- debug_object_deactivate
|
|
|
|
- debug_object_destroy
|
|
|
|
- debug_object_free
|
|
|
|
- debug_object_assert_init
|
|
|
|
Each of these functions takes the address of the real object and a
|
|
pointer to the object type specific debug description structure.
|
|
|
|
Each detected error is reported in the statistics and a limited number
|
|
of errors are printk'ed including a full stack trace.
|
|
|
|
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.
|
|
|
|
Debug functions
|
|
===============
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_init
|
|
|
|
This function is called whenever the initialization function of a real
|
|
object is called.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_init_on_stack
|
|
|
|
This function is called whenever the initialization function of a real
|
|
object which resides on the stack is called.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_activate
|
|
|
|
This function is called whenever the activation function of a real
|
|
object is called.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
When the activation is legitimate, then the state of the associated
|
|
tracker object is set to ODEBUG_STATE_ACTIVE.
|
|
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_deactivate
|
|
|
|
This function is called whenever the deactivation function of a real
|
|
object is called.
|
|
|
|
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.
|
|
|
|
When the deactivation is legitimate, then the state of the associated
|
|
tracker object is set to ODEBUG_STATE_INACTIVE.
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_destroy
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
When the destruction is legitimate, then the state of the associated
|
|
tracker object is set to ODEBUG_STATE_DESTROYED.
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_free
|
|
|
|
This function is called before an object is freed.
|
|
|
|
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.
|
|
|
|
Note that debug_object_free removes the object from the tracker. Later
|
|
usage of the object is detected by the other debug checks.
|
|
|
|
|
|
.. kernel-doc:: lib/debugobjects.c
|
|
:functions: debug_object_assert_init
|
|
|
|
This function is called to assert that an object has been initialized.
|
|
|
|
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.
|
|
|
|
When the real object is already tracked by debugobjects it is ignored.
|
|
|
|
Fixup functions
|
|
===============
|
|
|
|
Debug object type description structure
|
|
---------------------------------------
|
|
|
|
.. kernel-doc:: include/linux/debugobjects.h
|
|
:internal:
|
|
|
|
fixup_init
|
|
-----------
|
|
|
|
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.
|
|
|
|
Called from debug_object_init when the object state is:
|
|
|
|
- ODEBUG_STATE_ACTIVE
|
|
|
|
The function returns true when the fixup was successful, otherwise
|
|
false. The return value is used to update the statistics.
|
|
|
|
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.
|
|
|
|
fixup_activate
|
|
---------------
|
|
|
|
This function is called from the debug code whenever a problem in
|
|
debug_object_activate is detected.
|
|
|
|
Called from debug_object_activate when the object state is:
|
|
|
|
- ODEBUG_STATE_NOTAVAILABLE
|
|
|
|
- ODEBUG_STATE_ACTIVE
|
|
|
|
The function returns true when the fixup was successful, otherwise
|
|
false. The return value is used to update the statistics.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
fixup_destroy
|
|
--------------
|
|
|
|
This function is called from the debug code whenever a problem in
|
|
debug_object_destroy is detected.
|
|
|
|
Called from debug_object_destroy when the object state is:
|
|
|
|
- ODEBUG_STATE_ACTIVE
|
|
|
|
The function returns true when the fixup was successful, otherwise
|
|
false. The return value is used to update the statistics.
|
|
|
|
fixup_free
|
|
-----------
|
|
|
|
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.
|
|
|
|
Called from debug_object_free() or debug_check_no_obj_freed() when
|
|
the object state is:
|
|
|
|
- ODEBUG_STATE_ACTIVE
|
|
|
|
The function returns true when the fixup was successful, otherwise
|
|
false. The return value is used to update the statistics.
|
|
|
|
fixup_assert_init
|
|
-------------------
|
|
|
|
This function is called from the debug code whenever a problem in
|
|
debug_object_assert_init is detected.
|
|
|
|
Called from debug_object_assert_init() with a hardcoded state
|
|
ODEBUG_STATE_NOTAVAILABLE when the object is not found in the debug
|
|
bucket.
|
|
|
|
The function returns true when the fixup was successful, otherwise
|
|
false. The return value is used to update the statistics.
|
|
|
|
Note, this function should make sure debug_object_init() is called
|
|
before returning.
|
|
|
|
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.
|
|
|
|
Known Bugs And Assumptions
|
|
==========================
|
|
|
|
None (knock on wood).
|