[rtems commit] score: Fix _User_extensions_Thread_switch() (SMP)

[Sebastian Huber]

Module:    rtems
Branch:    master
Commit:    26333f2ad09fc2ecd574fb167862520493c63ee3
Changeset: http://git.rtems.org/rtems/commit/?id=26333f2ad09fc2ecd574fb167862520493c63ee3

Author:    Sebastian Huber <sebastian.huber at embedded-brains.de>
Date:      Fri Feb  8 10:16:07 2019 +0100

score: Fix _User_extensions_Thread_switch() (SMP)

We have to read the first node again once we obtained the lock since it
may have aready changed.

---

 cpukit/include/rtems/score/userextimpl.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/cpukit/include/rtems/score/userextimpl.h b/cpukit/include/rtems/score/userextimpl.h
index 7748659..77357b9 100644
--- a/cpukit/include/rtems/score/userextimpl.h
+++ b/cpukit/include/rtems/score/userextimpl.h
@@ -256,9 +256,13 @@ static inline void _User_extensions_Thread_switch(
   Thread_Control *heir
 )
 {
-  const Chain_Control *chain = &_User_extensions_Switches_list;
-  const Chain_Node    *tail = _Chain_Immutable_tail( chain );
-  const Chain_Node    *node = _Chain_Immutable_first( chain );
+  const Chain_Control *chain;
+  const Chain_Node    *tail;
+  const Chain_Node    *node;
+
+  chain = &_User_extensions_Switches_list;
+  tail = _Chain_Immutable_tail( chain );
+  node = _Chain_Immutable_first( chain );
 
   if ( node != tail ) {
     Per_CPU_Control *cpu_self;
@@ -273,6 +277,10 @@ static inline void _User_extensions_Thread_switch(
 #endif
     _Per_CPU_Acquire( cpu_self );
 
+#if defined(RTEMS_SMP)
+    node = _Chain_Immutable_first( chain );
+#endif
+
     while ( node != tail ) {
       const User_extensions_Switch_control *extension =
         (const User_extensions_Switch_control *) node;