[PATCH v4] debugobjects: print more data

[PATCH v4] debugobjects: print more data

[Stanislaw Gruszka]

On complex subsystems like mac80211, structures may include many timers
and works. In such case, based only on call trace and object type is hard
to conclude where bug could possibly be.

Patch extend debug object descriptor to additional print function.
If defined, it provide per object debugging data. Patch contains print
methods for timer_list, work_struct and hrtimer. They print object
pointer, and (what is most useful) corresponding function callback
symbol name.

On main print function I changed WARN to printk to avoid "cut off" lines
and keep all informations together.

I tested patch with timer_list bug in mac80211, I get following output
wen bug was triggered:

ODEBUG: free active (active state 0) object type: timer_list
Pid: 8195, comm: rmmod Not tainted 2.6.38-rc5-wl+ #29
Call Trace:
 [<ffffffff8122783f>] ? debug_print_object+0x5f/0x80
 [<ffffffff81227ee5>] ? debug_check_no_obj_freed+0x125/0x210
 [<ffffffff8109ecd7>] ? debug_check_no_locks_freed+0xf7/0x170
 [<ffffffff81156942>] ? kfree+0xc2/0x2f0
 [<ffffffff813ecf95>] ? netdev_release+0x45/0x60
 [<ffffffff812f1927>] ? device_release+0x27/0xa0
 [<ffffffff812176dd>] ? kobject_release+0x8d/0x1a0
 [<ffffffff81217650>] ? kobject_release+0x0/0x1a0
 [<ffffffff81218cb7>] ? kref_put+0x37/0x70
 [<ffffffff81217557>] ? kobject_put+0x27/0x60
 [<ffffffff813d66db>] ? netdev_run_todo+0x1ab/0x270
 [<ffffffff813e80ee>] ? rtnl_unlock+0xe/0x10
 [<ffffffffa0565188>] ? ieee80211_unregister_hw+0x58/0x120 [mac80211]
 [<ffffffffa062ced7>] ? iwl_pci_remove+0xdb/0x22a [iwlagn]
 [<ffffffff8123d562>] ? pci_device_remove+0x52/0x120
 [<ffffffff812f5ac5>] ? __device_release_driver+0x75/0xe0
 [<ffffffff812f5c08>] ? driver_detach+0xd8/0xe0
 [<ffffffff812f49d1>] ? bus_remove_driver+0x91/0x100
 [<ffffffff812f6422>] ? driver_unregister+0x62/0xa0
 [<ffffffff8123d914>] ? pci_unregister_driver+0x44/0xa0
 [<ffffffffa062cdf5>] ? iwl_exit+0x15/0x1c [iwlagn]
 [<ffffffff810ab592>] ? sys_delete_module+0x1a2/0x270
 [<ffffffff814992c9>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff8100bf42>] ? system_call_fastpath+0x16/0x1b
ODEBUG timer_list: ffff8801230cf138 function: ieee80211_sta_conn_mon_timer+0x0/0x40 [mac80211]

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
---
v1 -> v2:
 - do not invent custom functions for print symbols
 - remove not necessary null check, use same call convention like other
   methods
 - fix stray whitespace
 - print only symbol name (no function pointer)
v2 -> v3:
 - remove remaining kallsyms changes
v3 -> v4:
 - make callbacks static

 include/linux/debugobjects.h |    4 +++-
 kernel/hrtimer.c             |    9 +++++++++
 kernel/timer.c               |    9 +++++++++
 kernel/workqueue.c           |    8 ++++++++
 lib/debugobjects.c           |    7 +++++--
 5 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/include/linux/debugobjects.h b/include/linux/debugobjects.h
index 597692f..89f115e 100644
--- a/include/linux/debugobjects.h
+++ b/include/linux/debugobjects.h
@@ -34,7 +34,9 @@ struct debug_obj {
 
 /**
  * struct debug_obj_descr - object type specific debug description structure
+ *
  * @name:		name of the object typee
+ * @print:		function printing extra debug data
  * @fixup_init:		fixup function, which is called when the init check
  *			fails
  * @fixup_activate:	fixup function, which is called when the activate check
@@ -46,7 +48,7 @@ struct debug_obj {
  */
 struct debug_obj_descr {
 	const char		*name;
-
+	void (*print)		(void *addr);
 	int (*fixup_init)	(void *addr, enum debug_obj_state state);
 	int (*fixup_activate)	(void *addr, enum debug_obj_state state);
 	int (*fixup_destroy)	(void *addr, enum debug_obj_state state);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 0c8d7c0..60b1418 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -334,6 +334,14 @@ EXPORT_SYMBOL_GPL(ktime_add_safe);
 
 static struct debug_obj_descr hrtimer_debug_descr;
 
+static void hrtimer_debug_print(void *addr)
+{
+	struct hrtimer *hrtimer = addr;
+
+	printk(KERN_ERR "ODEBUG hrtimer: %p function: %pS\n",
+	       hrtimer, hrtimer->function);
+}
+
 /*
  * fixup_init is called when:
  * - an active object is initialized
@@ -393,6 +401,7 @@ static int hrtimer_fixup_free(void *addr, enum debug_obj_state state)
 
 static struct debug_obj_descr hrtimer_debug_descr = {
 	.name		= "hrtimer",
+	.print		= hrtimer_debug_print,
 	.fixup_init	= hrtimer_fixup_init,
 	.fixup_activate	= hrtimer_fixup_activate,
 	.fixup_free	= hrtimer_fixup_free,
diff --git a/kernel/timer.c b/kernel/timer.c
index d645992..6d857a2 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -404,6 +404,14 @@ static void timer_stats_account_timer(struct timer_list *timer) {}
 
 static struct debug_obj_descr timer_debug_descr;
 
+static void timer_debug_print(void *addr)
+{
+	struct timer_list *timer = addr;
+
+	printk(KERN_ERR "ODEBUG timer_list: %p function: %pS\n",
+	       timer, timer->function);
+}
+
 /*
  * fixup_init is called when:
  * - an active object is initialized
@@ -477,6 +485,7 @@ static int timer_fixup_free(void *addr, enum debug_obj_state state)
 
 static struct debug_obj_descr timer_debug_descr = {
 	.name		= "timer_list",
+	.print		= timer_debug_print,
 	.fixup_init	= timer_fixup_init,
 	.fixup_activate	= timer_fixup_activate,
 	.fixup_free	= timer_fixup_free,
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 11869fa..4747c4f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -314,6 +314,13 @@ static inline int __next_wq_cpu(int cpu, const struct cpumask *mask,
 
 static struct debug_obj_descr work_debug_descr;
 
+static void work_debug_print(void *addr)
+{
+	struct work_struct *work = addr;
+
+	printk(KERN_ERR "ODEBUG work_struct: %p func: %pS\n", work, work->func);
+}
+
 /*
  * fixup_init is called when:
  * - an active object is initialized
@@ -385,6 +392,7 @@ static int work_fixup_free(void *addr, enum debug_obj_state state)
 
 static struct debug_obj_descr work_debug_descr = {
 	.name		= "work_struct",
+	.print		= work_debug_print,
 	.fixup_init	= work_fixup_init,
 	.fixup_activate	= work_fixup_activate,
 	.fixup_free	= work_fixup_free,
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index deebcc5..c755c0f 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -253,10 +253,13 @@ static void debug_print_object(struct debug_obj *obj, char *msg)
 
 	if (limit < 5 && obj->descr != descr_test) {
 		limit++;
-		WARN(1, KERN_ERR "ODEBUG: %s %s (active state %u) "
-				 "object type: %s\n",
+		printk(KERN_ERR "ODEBUG: %s %s (active state %u) "
+				"object type: %s\n",
 			msg, obj_states[obj->state], obj->astate,
 			obj->descr->name);
+		dump_stack();
+		if (obj->descr->print)
+			obj->descr->print(obj->object);
 	}
 	debug_objects_warnings++;
 }
-- 
1.7.1

Re: [PATCH v4] debugobjects: print more data

[Thomas Gleixner]

On Tue, 22 Feb 2011, Stanislaw Gruszka wrote:
> On main print function I changed WARN to printk to avoid "cut off" lines
> and keep all informations together.

Sorry for not noticing the problem with this earlier. It makes bug
reporting for Joe user harder than it is now. The WARN based output is
automatically captured by kerneloops and other tools. Your change
prevents it.

And we can be more clever about it.

>  struct debug_obj_descr {
>  	const char		*name;
> -
> +	void (*print)		(void *addr);

So we could change that function to be

        void *(debug_hint)	(void *addr);

And let it do:

static void *debug_hint(void *addr)
{
	return ((struct hrtimer *) addr)->function;
}

The object pointer itself is already known and pretty pointless. There
is really no debug value in the pointer itself.

That would change debug_print_object() to:

     void *hint = descr->debug_hint ? descr->debug_hint(obj->object) : NULL;

and make

    WARN(1, KERN_ERR "ODEBUG: %s %s (active state %u) object type: %s hint: %pS\n",
  			msg, obj_states[obj->state], obj->astate,
  			obj->descr->name, hint);

So we get the valuable additional information w/o losing the ability
of automated bug reports. And I think all we ever want is something
like a callback function, which helps us to identify the object.

Thanks,

	tglx