debugobjects: insulate non-fixup logic related to static obj from fixup callbacks

When activating a static object we need make sure that the object is
tracked in the object tracker.  If it is a non-static object then the
activation is illegal.

In previous implementation, each subsystem need take care of this in
their fixup callbacks.  Actually we can put it into debugobjects core.
Thus we can save duplicated code, and have *pure* fixup callbacks.

To achieve this, a new callback "is_static_object" is introduced to let
the type specific code decide whether a object is static or not.  If
yes, we take it into object tracker, otherwise give warning and invoke
fixup callback.

This change has paassed debugobjects selftest, and I also do some test
with all debugobjects supports enabled.

At last, I have a concern about the fixups that can it change the object
which is in incorrect state on fixup? Because the 'addr' may not point
to any valid object if a non-static object is not tracked.  Then Change
such object can overwrite someone's memory and cause unexpected
behaviour.  For example, the timer_fixup_activate bind timer to function
stub_timer.

Link: http://lkml.kernel.org/r/1462576157-14539-1-git-send-email-changbin.du@intel.com
[changbin.du@intel.com: improve code comments where invoke the new is_static_object callback]
  Link: http://lkml.kernel.org/r/1462777431-8171-1-git-send-email-changbin.du@intel.com
Signed-off-by: Du, Changbin <changbin.du@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Josh Triplett <josh@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 29 deletions

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index be33481a4da1..3a95f9728778 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -489,6 +489,14 @@ static void *timer_debug_hint(void *addr)
 	return ((struct timer_list *) addr)->function;
 }
 
+static bool timer_is_static_object(void *addr)
+{
+	struct timer_list *timer = addr;
+
+	return (timer->entry.pprev == NULL &&
+		timer->entry.next == TIMER_ENTRY_STATIC);
+}
+
 /*
  * fixup_init is called when:
  * - an active object is initialized
@@ -516,30 +524,16 @@ static void stub_timer(unsigned long data)
 /*
  * fixup_activate is called when:
  * - an active object is activated
- * - an unknown object is activated (might be a statically initialized object)
+ * - an unknown non-static object is activated
  */
 static bool timer_fixup_activate(void *addr, enum debug_obj_state state)
 {
 	struct timer_list *timer = addr;
 
 	switch (state) {
-
 	case ODEBUG_STATE_NOTAVAILABLE:
-		/*
-		 * This is not really a fixup. The timer was
-		 * statically initialized. We just make sure that it
-		 * is tracked in the object tracker.
-		 */
-		if (timer->entry.pprev == NULL &&
-		    timer->entry.next == TIMER_ENTRY_STATIC) {
-			debug_object_init(timer, &timer_debug_descr);
-			debug_object_activate(timer, &timer_debug_descr);
-			return false;
-		} else {
-			setup_timer(timer, stub_timer, 0);
-			return true;
-		}
-		return false;
+		setup_timer(timer, stub_timer, 0);
+		return true;
 
 	case ODEBUG_STATE_ACTIVE:
 		WARN_ON(1);
@@ -577,18 +571,8 @@ static bool timer_fixup_assert_init(void *addr, enum debug_obj_state state)
 
 	switch (state) {
 	case ODEBUG_STATE_NOTAVAILABLE:
-		if (timer->entry.next == TIMER_ENTRY_STATIC) {
-			/*
-			 * This is not really a fixup. The timer was
-			 * statically initialized. We just make sure that it
-			 * is tracked in the object tracker.
-			 */
-			debug_object_init(timer, &timer_debug_descr);
-			return false;
-		} else {
-			setup_timer(timer, stub_timer, 0);
-			return true;
-		}
+		setup_timer(timer, stub_timer, 0);
+		return true;
 	default:
 		return false;
 	}
@@ -597,6 +581,7 @@ static bool timer_fixup_assert_init(void *addr, enum debug_obj_state state)
 static struct debug_obj_descr timer_debug_descr = {
 	.name			= "timer_list",
 	.debug_hint		= timer_debug_hint,
+	.is_static_object	= timer_is_static_object,
 	.fixup_init		= timer_fixup_init,
 	.fixup_activate		= timer_fixup_activate,
 	.fixup_free		= timer_fixup_free,