score: Use chain iterator for user extensions

Add a lock and use a chain iterator for safe iteration during concurrent
user extension addition and removal.

Ensure that dynamically added thread delete and fatal extensions are
called in reverse order.

Update #2555.
Update #2692.

6 files changed, 184 insertions, 40 deletions

diff --git a/cpukit/score/include/rtems/score/thread.h b/cpukit/score/include/rtems/score/thread.h
index d9f1eb2d6d..4da4a341d6 100644
--- a/cpukit/score/include/rtems/score/thread.h
+++ b/cpukit/score/include/rtems/score/thread.h
@@ -48,6 +48,8 @@ struct Scheduler_Control;
 
 struct Scheduler_Node;
 
+struct User_extensions_Iterator;
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -899,6 +901,11 @@ struct _Thread_Control {
   struct _pthread_cleanup_context *last_cleanup_context;
 
   /**
+   * @brief LIFO list of user extensions iterators.
+   */
+  struct User_extensions_Iterator *last_user_extensions_iterator;
+
+  /**
    * @brief Variable length array of user extension pointers.
    *
    * The length is defined by the application via <rtems/confdefs.h>.
diff --git a/cpukit/score/include/rtems/score/userextimpl.h b/cpukit/score/include/rtems/score/userextimpl.h
index 8c2a1fac4d..e175c9f0a5 100644
--- a/cpukit/score/include/rtems/score/userextimpl.h
+++ b/cpukit/score/include/rtems/score/userextimpl.h
@@ -19,6 +19,7 @@
 #define _RTEMS_SCORE_USEREXTIMPL_H
 
 #include <rtems/score/userext.h>
+#include <rtems/score/isrlock.h>
 #include <rtems/score/chainimpl.h>
 #include <rtems/score/percpu.h>
 
@@ -36,9 +37,41 @@ extern "C" {
 /**@{**/
 
 /**
+ * @brief Chain iterator for dynamic user extensions.
+ *
+ * Since user extensions may delete or restart the executing thread, we must
+ * clean up registered iterators.
+ *
+ * @see _User_extensions_Iterate(), _User_extensions_Destroy_iterators() and
+ *   Thread_Control::last_user_extensions_iterator.
+ */
+typedef struct User_extensions_Iterator {
+  Chain_Iterator                   Iterator;
+  struct User_extensions_Iterator *previous;
+} User_extensions_Iterator;
+
+typedef struct {
+  /**
+   * @brief Active dynamically added user extensions.
+   */
+  Chain_Control Active;
+
+  /**
+   * @brief Chain iterator registration.
+   */
+  Chain_Iterator_registry Iterators;
+
+  /**
+   * @brief Lock to protect User_extensions_List::Active and
+   * User_extensions_List::Iterators.
+   */
+  ISR_LOCK_MEMBER( Lock )
+} User_extensions_List;
+
+/**
  * @brief List of active extensions.
  */
-extern Chain_Control _User_extensions_List;
+extern User_extensions_List _User_extensions_List;
 
 /**
  * @brief List of active task switch extensions.
@@ -153,11 +186,13 @@ void _User_extensions_Thread_terminate_visitor(
  * @brief Iterates through all user extensions and calls the visitor for each.
  *
  * @param[in, out] arg The argument passed to the visitor.
- * @param[in] visitor is the visitor for each extension.
+ * @param[in] visitor The visitor for each extension.
+ * @param[in] direction The iteration direction for dynamic extensions.
  */
 void _User_extensions_Iterate(
-  void                    *arg,
-  User_extensions_Visitor  visitor
+  void                     *arg,
+  User_extensions_Visitor   visitor,
+  Chain_Iterator_direction  direction
 );
 
 /** @} */
@@ -171,7 +206,11 @@ static inline bool _User_extensions_Thread_create( Thread_Control *created )
 {
   User_extensions_Thread_create_context ctx = { created, true };
 
-  _User_extensions_Iterate( &ctx, _User_extensions_Thread_create_visitor );
+  _User_extensions_Iterate(
+    &ctx,
+    _User_extensions_Thread_create_visitor,
+    CHAIN_ITERATOR_FORWARD
+  );
 
   return ctx.ok;
 }
@@ -180,7 +219,8 @@ static inline void _User_extensions_Thread_delete( Thread_Control *deleted )
 {
   _User_extensions_Iterate(
     deleted,
-    _User_extensions_Thread_delete_visitor
+    _User_extensions_Thread_delete_visitor,
+    CHAIN_ITERATOR_BACKWARD
   );
 }
 
@@ -188,7 +228,8 @@ static inline void _User_extensions_Thread_start( Thread_Control *started )
 {
   _User_extensions_Iterate(
     started,
-    _User_extensions_Thread_start_visitor
+    _User_extensions_Thread_start_visitor,
+    CHAIN_ITERATOR_FORWARD
   );
 }
 
@@ -196,7 +237,8 @@ static inline void _User_extensions_Thread_restart( Thread_Control *restarted )
 {
   _User_extensions_Iterate(
     restarted,
-    _User_extensions_Thread_restart_visitor
+    _User_extensions_Thread_restart_visitor,
+    CHAIN_ITERATOR_FORWARD
   );
 }
 
@@ -204,7 +246,8 @@ static inline void _User_extensions_Thread_begin( Thread_Control *executing )
 {
   _User_extensions_Iterate(
     executing,
-    _User_extensions_Thread_begin_visitor
+    _User_extensions_Thread_begin_visitor,
+    CHAIN_ITERATOR_FORWARD
   );
 }
 
@@ -239,7 +282,8 @@ static inline void _User_extensions_Thread_exitted( Thread_Control *executing )
 {
   _User_extensions_Iterate(
     executing,
-    _User_extensions_Thread_exitted_visitor
+    _User_extensions_Thread_exitted_visitor,
+    CHAIN_ITERATOR_FORWARD
   );
 }
 
@@ -251,7 +295,11 @@ static inline void _User_extensions_Fatal(
 {
   User_extensions_Fatal_context ctx = { source, is_internal, error };
 
-  _User_extensions_Iterate( &ctx, _User_extensions_Fatal_visitor );
+  _User_extensions_Iterate(
+    &ctx,
+    _User_extensions_Fatal_visitor,
+    CHAIN_ITERATOR_BACKWARD
+  );
 }
 
 static inline void _User_extensions_Thread_terminate(
@@ -260,10 +308,46 @@ static inline void _User_extensions_Thread_terminate(
 {
   _User_extensions_Iterate(
     executing,
-    _User_extensions_Thread_terminate_visitor
+    _User_extensions_Thread_terminate_visitor,
+    CHAIN_ITERATOR_FORWARD
+  );
+}
+
+static inline void _User_extensions_Acquire( ISR_lock_Context *lock_context )
+{
+  _ISR_lock_ISR_disable_and_acquire(
+    &_User_extensions_List.Lock,
+    lock_context
   );
 }
 
+static inline void _User_extensions_Release( ISR_lock_Context *lock_context )
+{
+  _ISR_lock_Release_and_ISR_enable(
+    &_User_extensions_List.Lock,
+    lock_context
+  );
+}
+
+static inline void _User_extensions_Destroy_iterators(
+  Thread_Control *the_thread
+)
+{
+  ISR_lock_Context          lock_context;
+  User_extensions_Iterator *iter;
+
+  _User_extensions_Acquire( &lock_context );
+
+  iter = the_thread->last_user_extensions_iterator;
+
+  while ( iter != NULL ) {
+    _Chain_Iterator_destroy( &iter->Iterator );
+    iter = iter->previous;
+  }
+
+  _User_extensions_Release( &lock_context );
+}
+
 /** @} */
 
 /** @} */
diff --git a/cpukit/score/src/threadrestart.c b/cpukit/score/src/threadrestart.c
index 59754a86fb..13b4365b35 100644
--- a/cpukit/score/src/threadrestart.c
+++ b/cpukit/score/src/threadrestart.c
@@ -97,6 +97,7 @@ static void _Thread_Free( Thread_Control *the_thread )
     _Objects_Get_information_id( the_thread->Object.id );
 
   _User_extensions_Thread_delete( the_thread );
+  _User_extensions_Destroy_iterators( the_thread );
   _ISR_lock_Destroy( &the_thread->Keys.Lock );
   _Scheduler_Node_destroy( _Scheduler_Get( the_thread ), the_thread );
   _ISR_lock_Destroy( &the_thread->Timer.Lock );
@@ -255,6 +256,7 @@ void _Thread_Life_action_handler(
 
       executing->Life.state = THREAD_LIFE_NORMAL;
 
+      _User_extensions_Destroy_iterators( executing );
       _Thread_Load_environment( executing );
       _Thread_Restart_self( executing );
       RTEMS_UNREACHABLE();
diff --git a/cpukit/score/src/userextaddset.c b/cpukit/score/src/userextaddset.c
index f34ad0072f..19bbd361e9 100644
--- a/cpukit/score/src/userextaddset.c
+++ b/cpukit/score/src/userextaddset.c
@@ -20,20 +20,20 @@
 #endif
 
 #include <rtems/score/userextimpl.h>
-#include <rtems/score/objectimpl.h>
 #include <rtems/score/percpu.h>
-#include <rtems/score/sysstate.h>
 
 void _User_extensions_Add_set(
   User_extensions_Control *the_extension
 )
 {
-  _Assert(
-    _Objects_Allocator_is_owner()
-      || _System_state_Is_before_multitasking( _System_state_Get() )
-  );
+  ISR_lock_Context lock_context;
 
-  _Chain_Append_unprotected( &_User_extensions_List, &the_extension->Node );
+  _User_extensions_Acquire( &lock_context );
+  _Chain_Append_unprotected(
+    &_User_extensions_List.Active,
+    &the_extension->Node
+  );
+  _User_extensions_Release( &lock_context );
 
   /*
    * If a switch handler is present, append it to the switch chain.
diff --git a/cpukit/score/src/userextiterate.c b/cpukit/score/src/userextiterate.c
index beeee9570b..6cb877452b 100644
--- a/cpukit/score/src/userextiterate.c
+++ b/cpukit/score/src/userextiterate.c
@@ -7,10 +7,10 @@
  */
 
 /*
- * Copyright (c) 2012 embedded brains GmbH.  All rights reserved.
+ * Copyright (c) 2012, 2016 embedded brains GmbH.  All rights reserved.
  *
  *  embedded brains GmbH
- *  Obere Lagerstr. 30
+ *  Dornierstr. 4
  *  82178 Puchheim
  *  Germany
  *  <rtems@embedded-brains.de>
@@ -27,7 +27,16 @@
 #include <rtems/config.h>
 #include <rtems/score/userextimpl.h>
 
-CHAIN_DEFINE_EMPTY( _User_extensions_List );
+#include <pthread.h>
+
+User_extensions_List _User_extensions_List = {
+  CHAIN_INITIALIZER_EMPTY( _User_extensions_List.Active ),
+  CHAIN_ITERATOR_REGISTRY_INITIALIZER( _User_extensions_List.Iterators )
+#if defined(RTEMS_SMP)
+  ,
+  ISR_LOCK_INITIALIZER( "User Extensions List" )
+#endif
+};
 
 void _User_extensions_Thread_create_visitor(
   Thread_Control              *executing,
@@ -139,17 +148,24 @@ void _User_extensions_Thread_terminate_visitor(
 }
 
 void _User_extensions_Iterate(
-  void                    *arg,
-  User_extensions_Visitor  visitor
+  void                     *arg,
+  User_extensions_Visitor   visitor,
+  Chain_Iterator_direction  direction
 )
 {
-  Thread_Control *executing = _Thread_Get_executing();
-  const User_extensions_Table *callouts_current =
-    rtems_configuration_get_user_extension_table();
-  const User_extensions_Table *callouts_end =
-    callouts_current + rtems_configuration_get_number_of_initial_extensions();
-  const Chain_Node *node;
-  const Chain_Node *tail;
+  Thread_Control              *executing;
+  const User_extensions_Table *callouts_current;
+  const User_extensions_Table *callouts_end;
+  const Chain_Node            *end;
+  Chain_Node                  *node;
+  User_extensions_Iterator     iter;
+  ISR_lock_Context             lock_context;
+
+  executing = _Thread_Get_executing();
+
+  callouts_current = rtems_configuration_get_user_extension_table();
+  callouts_end = callouts_current
+    + rtems_configuration_get_number_of_initial_extensions();
 
   while ( callouts_current != callouts_end ) {
     (*visitor)( executing, arg, callouts_current );
@@ -157,14 +173,44 @@ void _User_extensions_Iterate(
     ++callouts_current;
   }
 
-  node = _Chain_Immutable_first( &_User_extensions_List );
-  tail = _Chain_Immutable_tail( &_User_extensions_List );
-  while ( node != tail ) {
-    const User_extensions_Control *extension =
-      (const User_extensions_Control *) node;
+  if ( direction == CHAIN_ITERATOR_FORWARD ) {
+    end = _Chain_Immutable_tail( &_User_extensions_List.Active );
+  } else {
+    end = _Chain_Immutable_head( &_User_extensions_List.Active );
+  }
+
+  _User_extensions_Acquire( &lock_context );
+
+  _Chain_Iterator_initialize(
+    &_User_extensions_List.Active,
+    &_User_extensions_List.Iterators,
+    &iter.Iterator,
+    direction
+  );
+
+  if ( executing != NULL ) {
+    iter.previous = executing->last_user_extensions_iterator;
+    executing->last_user_extensions_iterator = &iter;
+  }
+
+  while ( ( node = _Chain_Iterator_next( &iter.Iterator ) ) != end ) {
+    const User_extensions_Control *extension;
+
+    _Chain_Iterator_set_position( &iter.Iterator, node );
+
+    _User_extensions_Release( &lock_context );
 
-    (*visitor)( executing, arg, &extension->Callouts );
+    extension = (const User_extensions_Control *) node;
+    ( *visitor )( executing, arg, &extension->Callouts );
 
-    node = _Chain_Immutable_next( node );
+    _User_extensions_Acquire( &lock_context );
   }
+
+  if ( executing != NULL ) {
+    executing->last_user_extensions_iterator = iter.previous;
+  }
+
+  _Chain_Iterator_destroy( &iter.Iterator );
+
+  _User_extensions_Release( &lock_context );
 }
diff --git a/cpukit/score/src/userextremoveset.c b/cpukit/score/src/userextremoveset.c
index 5b3fdd1aea..b25cc344b4 100644
--- a/cpukit/score/src/userextremoveset.c
+++ b/cpukit/score/src/userextremoveset.c
@@ -20,16 +20,21 @@
 #endif
 
 #include <rtems/score/userextimpl.h>
-#include <rtems/score/objectimpl.h>
 #include <rtems/score/percpu.h>
 
 void _User_extensions_Remove_set (
   User_extensions_Control  *the_extension
 )
 {
-  _Assert( _Objects_Allocator_is_owner() );
+  ISR_lock_Context lock_context;
 
+  _User_extensions_Acquire( &lock_context );
+  _Chain_Iterator_registry_update(
+    &_User_extensions_List.Iterators,
+    &the_extension->Node
+  );
   _Chain_Extract_unprotected( &the_extension->Node );
+  _User_extensions_Release( &lock_context );
 
   /*
    * If a switch handler is present, remove it.