Debugobjects transition check

Implement a basic state machine checker in the debugobjects.

This state machine checker detects races and inconsistencies within the "active"
life of a debugobject. The checker only keeps track of the current state; all
the state machine logic is kept at the object instance level.

The checker works by adding a supplementary "unsigned int astate" field to the
debug_obj structure. It keeps track of the current "active state" of the object.

The only constraints that are imposed on the states by the debugobjects system
is that:

- activation of an object sets the current active state to 0,
- deactivation of an object expects the current active state to be 0.

For the rest of the states, the state mapping is determined by the specific
object instance. Therefore, the logic keeping track of the state machine is
within the specialized instance, without any need to know about it at the
debugobject level.

The current object active state is changed by calling:

debug_object_active_state(addr, descr, expect, next)

where "expect" is the expected state and "next" is the next state to move to if
the expected state is found. A warning is generated if the expected is not
found.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David S. Miller <davem@davemloft.net>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: akpm@linux-foundation.org
CC: mingo@elte.hu
CC: laijs@cn.fujitsu.com
CC: dipankar@in.ibm.com
CC: josh@joshtriplett.org
CC: dvhltc@us.ibm.com
CC: niv@us.ibm.com
CC: peterz@infradead.org
CC: rostedt@goodmis.org
CC: Valdis.Kletnieks@vt.edu
CC: dhowells@redhat.com
CC: eric.dumazet@gmail.com
CC: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/debugobjects.h b/include/linux/debugobjects.h
index 8c243aaa86a7..597692f1fc8d 100644
--- a/include/linux/debugobjects.h
+++ b/include/linux/debugobjects.h
@@ -20,12 +20,14 @@ struct debug_obj_descr;
  * struct debug_obj - representaion of an tracked object
  * @node:       hlist node to link the object into the tracker list
  * @state:      tracked object state
+ * @astate:     current active state
  * @object:     pointer to the real object
  * @descr:      pointer to an object type specific debug description structure
  */
 struct debug_obj {
         struct hlist_node       node;
         enum debug_obj_state    state;
+        unsigned int            astate;
         void                    *object;
         struct debug_obj_descr  *descr;
 };
@@ -60,6 +62,15 @@ extern void debug_object_deactivate(void *addr, struct debug_obj_descr *descr);
 extern void debug_object_destroy   (void *addr, struct debug_obj_descr *descr);
 extern void debug_object_free      (void *addr, struct debug_obj_descr *descr);
 
+/*
+ * Active state:
+ * - Set at 0 upon initialization.
+ * - Must return to 0 before deactivation.
+ */
+extern void
+debug_object_active_state(void *addr, struct debug_obj_descr *descr,
+                          unsigned int expect, unsigned int next);
+
 extern void debug_objects_early_init(void);
 extern void debug_objects_mem_init(void);
 #else