From 691cc54c7d28542434d2b3ee4ddbad6a99312dec Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 30 Apr 2008 00:55:02 -0700 Subject: [PATCH] debugobjects: add documentation Add a DocBook for debugobjects. Signed-off-by: Thomas Gleixner Acked-by: Ingo Molnar Cc: Greg KH Cc: Randy Dunlap Cc: Kay Sievers Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/DocBook/Makefile | 2 +- Documentation/DocBook/debugobjects.tmpl | 391 ++++++++++++++++++++++++ 2 files changed, 392 insertions(+), 1 deletion(-) create mode 100644 Documentation/DocBook/debugobjects.tmpl diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 83966e94cc32..0eb0d027eb32 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -12,7 +12,7 @@ DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \ kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \ - mac80211.xml + mac80211.xml debugobjects.xml ### # The build process is as follows (targets): diff --git a/Documentation/DocBook/debugobjects.tmpl b/Documentation/DocBook/debugobjects.tmpl new file mode 100644 index 000000000000..7f5f218015fe --- /dev/null +++ b/Documentation/DocBook/debugobjects.tmpl @@ -0,0 +1,391 @@ + + + + + + Debug objects life time + + + + Thomas + Gleixner + +
+ tglx@linutronix.de +
+ + + + + + 2008 + Thomas Gleixner + + + + + 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. + + + + 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. + + + + 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 + + + + For more details see the file COPYING in the source + distribution of Linux. + + + + + + + + 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 + + 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 debugfs/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 + + Debug object function reference +!Elib/debugobjects.c + + + 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. + + + + + 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. + + + + + 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. + + + + + 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. + + + + + 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. + + + + + 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. + + + + + Fixup functions + + Debug object type description structure +!Iinclude/linux/debugobjects.h + + + 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 1 when the fixup was successful, + otherwise 0. 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 1 when the fixup was successful, + otherwise 0. 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 0 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 1 when the fixup was successful, + otherwise 0. 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 1 when the fixup was successful, + otherwise 0. The return value is used to update the + statistics. + + + + + Known Bugs And Assumptions + + None (knock on wood). + + + -- GitLab