[PATCH 3/4] score: Add and use _Giant_Drop()

[Sebastian Huber]

---
 cpukit/score/include/rtems/score/threaddispatch.h |   12 ++++++++++++
 cpukit/score/src/smp.c                            |    8 ++++++++
 cpukit/score/src/threaddispatchdisablelevel.c     |   13 +++++++++++++
 3 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/cpukit/score/include/rtems/score/threaddispatch.h b/cpukit/score/include/rtems/score/threaddispatch.h
index 2211662..4c2ecb0 100644
--- a/cpukit/score/include/rtems/score/threaddispatch.h
+++ b/cpukit/score/include/rtems/score/threaddispatch.h
@@ -109,6 +109,18 @@ RTEMS_INLINE_ROUTINE void _Thread_Dispatch_initialization( void )
   void _Giant_Release( void );
 
   /**
+   * @brief Releases the giant lock completely if held by the executing processor.
+   *
+   * The thread dispatch disable level is not altered by this function.
+   *
+   * The only use case for this operation is in
+   * _SMP_Request_processors_to_shutdown().
+   *
+   * @param[in] self_cpu The current processor index.
+   */
+  void _Giant_Drop( uint32_t self_cpu );
+
+  /**
    *  @brief Sets thread dispatch level to the value passed in.
    *
    * This routine sets thread dispatch level to the
diff --git a/cpukit/score/src/smp.c b/cpukit/score/src/smp.c
index 445a56a..41787e3 100644
--- a/cpukit/score/src/smp.c
+++ b/cpukit/score/src/smp.c
@@ -115,6 +115,14 @@ void _SMP_Request_processors_to_shutdown( void )
       _Per_CPU_Change_state( per_cpu, PER_CPU_STATE_SHUTDOWN );
     }
   }
+
+  /*
+   * We have to drop the Giant lock here in order to give other processors the
+   * opportunity to receive the inter-processor interrupts issued previously.
+   * In case the executing thread still holds SMP locks, then other processors
+   * already waiting for this SMP lock will spin forever.
+   */
+  _Giant_Drop( self );
 }
 
 void _SMP_Send_message( uint32_t cpu, uint32_t message )
diff --git a/cpukit/score/src/threaddispatchdisablelevel.c b/cpukit/score/src/threaddispatchdisablelevel.c
index a3dec99..ec5ac81 100644
--- a/cpukit/score/src/threaddispatchdisablelevel.c
+++ b/cpukit/score/src/threaddispatchdisablelevel.c
@@ -57,6 +57,19 @@ static void _Giant_Do_release( void )
   }
 }
 
+void _Giant_Drop( uint32_t self_cpu )
+{
+  Giant_Control *giant = &_Giant;
+
+  _Assert( _ISR_Get_level() != 0 );
+
+  if ( giant->owner_cpu == self_cpu ) {
+    giant->nest_level = 0;
+    giant->owner_cpu = NO_OWNER_CPU;
+    _SMP_lock_Release( &giant->lock );
+  }
+}
+
 uint32_t _Thread_Dispatch_increment_disable_level( void )
 {
   ISR_Level isr_level;
-- 
1.7.7