score: Simplify SMP processor state handling

The per-CPU states which control the SMP system initialization were added quite
early during the SMP support development.  Replace this initial implementation
with a simplified one.  There is no longer a global SMP lock required which
serialized the state changes of all processors.  The new implementation better
integrates with the per-CPU jobs.

4 files changed, 143 insertions, 190 deletions

diff --git a/cpukit/score/src/percpu.c b/cpukit/score/src/percpu.c
index 7fbc1c8637..3bacbd7f55 100644
--- a/cpukit/score/src/percpu.c
+++ b/cpukit/score/src/percpu.c
@@ -3,8 +3,8 @@
  *
  * @ingroup RTEMSScorePerCPU
  *
- * @brief This source file contains a definition of ::_Per_CPU_Information and
- *   the implementation of _Per_CPU_State_change().
+ * @brief This source file contains the uniprocessor definition of
+ *   ::_Per_CPU_Information and some static assertions.
  */
 
 /*
@@ -21,10 +21,6 @@
 #endif
 
 #include <rtems/score/percpu.h>
-#include <rtems/score/assert.h>
-#include <rtems/score/isrlock.h>
-#include <rtems/score/smpimpl.h>
-#include <rtems/config.h>
 
 RTEMS_STATIC_ASSERT(
   sizeof( CPU_Uint32ptr ) >= sizeof( uintptr_t ),
@@ -36,148 +32,7 @@ RTEMS_STATIC_ASSERT(
   CPU_Uint32ptr_greater_equal_uint32_t
 );
 
-#if defined(RTEMS_SMP)
-
-ISR_LOCK_DEFINE( static, _Per_CPU_State_lock, "Per-CPU State" )
-
-static void _Per_CPU_State_acquire( ISR_lock_Context *lock_context )
-{
-  _ISR_lock_ISR_disable_and_acquire( &_Per_CPU_State_lock, lock_context );
-}
-
-static void _Per_CPU_State_release( ISR_lock_Context *lock_context )
-{
-  _ISR_lock_Release_and_ISR_enable( &_Per_CPU_State_lock, lock_context );
-}
-
-static void _Per_CPU_State_busy_wait(
-  Per_CPU_Control *cpu,
-  Per_CPU_State new_state
-)
-{
-  Per_CPU_State state;
-
-  state = _Per_CPU_Get_state( cpu );
-
-  switch ( new_state ) {
-    case PER_CPU_STATE_REQUEST_START_MULTITASKING:
-      while (
-        state != PER_CPU_STATE_READY_TO_START_MULTITASKING
-          && state != PER_CPU_STATE_SHUTDOWN
-      ) {
-        _Per_CPU_Perform_jobs( cpu );
-        state = _Per_CPU_Get_state( cpu );
-      }
-      break;
-    case PER_CPU_STATE_UP:
-      while (
-        state != PER_CPU_STATE_REQUEST_START_MULTITASKING
-          && state != PER_CPU_STATE_SHUTDOWN
-      ) {
-        _Per_CPU_Perform_jobs( cpu );
-        state = _Per_CPU_Get_state( cpu );
-      }
-      break;
-    default:
-      /* No need to wait */
-      break;
-  }
-}
-
-static Per_CPU_State _Per_CPU_State_get_next(
-  Per_CPU_State current_state,
-  Per_CPU_State new_state
-)
-{
-  switch ( current_state ) {
-    case PER_CPU_STATE_INITIAL:
-      switch ( new_state ) {
-        case PER_CPU_STATE_READY_TO_START_MULTITASKING:
-        case PER_CPU_STATE_SHUTDOWN:
-          /* Change is acceptable */
-          break;
-        default:
-          new_state = PER_CPU_STATE_SHUTDOWN;
-          break;
-      }
-      break;
-    case PER_CPU_STATE_READY_TO_START_MULTITASKING:
-      switch ( new_state ) {
-        case PER_CPU_STATE_REQUEST_START_MULTITASKING:
-        case PER_CPU_STATE_SHUTDOWN:
-          /* Change is acceptable */
-          break;
-        default:
-          new_state = PER_CPU_STATE_SHUTDOWN;
-          break;
-      }
-      break;
-    case PER_CPU_STATE_REQUEST_START_MULTITASKING:
-      switch ( new_state ) {
-        case PER_CPU_STATE_UP:
-        case PER_CPU_STATE_SHUTDOWN:
-          /* Change is acceptable */
-          break;
-        default:
-          new_state = PER_CPU_STATE_SHUTDOWN;
-          break;
-      }
-      break;
-    default:
-      new_state = PER_CPU_STATE_SHUTDOWN;
-      break;
-  }
-
-  return new_state;
-}
-
-void _Per_CPU_State_change(
-  Per_CPU_Control *cpu,
-  Per_CPU_State new_state
-)
-{
-  ISR_lock_Context lock_context;
-  Per_CPU_State next_state;
-
-  _Per_CPU_State_busy_wait( cpu, new_state );
-
-  _Per_CPU_State_acquire( &lock_context );
-
-  next_state = _Per_CPU_State_get_next( _Per_CPU_Get_state( cpu ), new_state );
-  _Per_CPU_Set_state( cpu, next_state );
-
-  if ( next_state == PER_CPU_STATE_SHUTDOWN ) {
-    uint32_t cpu_max = rtems_configuration_get_maximum_processors();
-    uint32_t cpu_index;
-
-    for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
-      Per_CPU_Control *cpu_other = _Per_CPU_Get_by_index( cpu_index );
-
-      if ( cpu_other != cpu ) {
-        switch ( _Per_CPU_Get_state( cpu_other ) ) {
-          case PER_CPU_STATE_UP:
-            _SMP_Send_message( cpu_index, SMP_MESSAGE_SHUTDOWN );
-            break;
-          default:
-            /* Nothing to do */
-            break;
-        }
-
-        _Per_CPU_Set_state( cpu_other, PER_CPU_STATE_SHUTDOWN );
-      }
-    }
-  }
-
-  _Per_CPU_State_release( &lock_context );
-
-  if (
-    next_state == PER_CPU_STATE_SHUTDOWN
-      && new_state != PER_CPU_STATE_SHUTDOWN
-  ) {
-    _SMP_Fatal( SMP_FATAL_SHUTDOWN );
-  }
-}
-#else
+#if !defined(RTEMS_SMP)
   /*
    * On single core systems, we can efficiently directly access a single
    * statically allocated per cpu structure.  And the fields are initialized
diff --git a/cpukit/score/src/smp.c b/cpukit/score/src/smp.c
index 0488464da0..2c37cd6884 100644
--- a/cpukit/score/src/smp.c
+++ b/cpukit/score/src/smp.c
@@ -5,11 +5,12 @@
  *
  * @brief This source file contains the definition of ::_SMP_Online_processors
  *   and ::_SMP_Processor_maximum and the implementation of
- *   _SMP_Handler_initialize(), _SMP_Request_shutdown(),
- *   _SMP_Request_start_multitasking(), _SMP_Send_message(),
- *   _SMP_Send_message_broadcast(), _SMP_Send_message_multicast(),
- *   _SMP_Should_start_processor(), and
- *   _SMP_Start_multitasking_on_secondary_processor().
+ *   _SMP_Handler_initialize(),  _SMP_Process_message(),
+ *   _SMP_Request_shutdown(), _SMP_Request_start_multitasking(),
+ *   _SMP_Send_message(), _SMP_Send_message_broadcast(),
+ *   _SMP_Send_message_multicast(), _SMP_Should_start_processor(),
+ *   _SMP_Start_multitasking_on_secondary_processor(), and
+ *   _SMP_Try_to_process_message().
  */
 
 /*
@@ -35,6 +36,15 @@
   #error "deferred FP switch not implemented for SMP"
 #endif
 
+/**
+ * @brief Indicates if the system is ready to start multitasking.
+ *
+ * Only the boot processor is allowed to change this object.  If the object has
+ * a non-zero value and no fatal error occurred, then secondary processors
+ * should call _Thread_Start_multitasking() to start multiprocessing.
+ */
+static Atomic_Uint _SMP_Ready_to_start_multitasking;
+
 Processor_mask _SMP_Online_processors;
 
 uint32_t _SMP_Processor_maximum;
@@ -159,20 +169,38 @@ void _SMP_Request_start_multitasking( void )
   uint32_t         cpu_max;
   uint32_t         cpu_index;
 
-  cpu_self = _Per_CPU_Get();
-  _Per_CPU_State_change( cpu_self, PER_CPU_STATE_READY_TO_START_MULTITASKING );
-
   cpu_max = _SMP_Get_processor_maximum();
+  cpu_self = _Per_CPU_Get();
 
+  /*
+   * Wait until all other online processors reached the
+   * PER_CPU_STATE_READY_TO_START_MULTITASKING state.  The waiting is done
+   * without a timeout.  If secondary processors cannot reach this state, then
+   * it is expected that they indicate this failure with an
+   * ::SMP_MESSAGE_SHUTDOWN message or reset the system.
+   */
   for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
     Per_CPU_Control *cpu;
 
     cpu = _Per_CPU_Get_by_index( cpu_index );
 
-    if ( _Per_CPU_Is_processor_online( cpu ) ) {
-      _Per_CPU_State_change( cpu, PER_CPU_STATE_REQUEST_START_MULTITASKING );
+    if ( cpu != cpu_self && _Per_CPU_Is_processor_online( cpu ) ) {
+      while (
+        _Per_CPU_Get_state( cpu ) != PER_CPU_STATE_READY_TO_START_MULTITASKING
+      ) {
+        _SMP_Try_to_process_message(
+          cpu_self,
+          _Atomic_Load_ulong( &cpu_self->message, ATOMIC_ORDER_RELAXED )
+        );
+      }
     }
   }
+
+  _Atomic_Store_uint(
+    &_SMP_Ready_to_start_multitasking,
+    1U,
+    ATOMIC_ORDER_RELEASE
+  );
 }
 
 bool _SMP_Should_start_processor( uint32_t cpu_index )
@@ -183,6 +211,22 @@ bool _SMP_Should_start_processor( uint32_t cpu_index )
   return _Scheduler_Should_start_processor( assignment );
 }
 
+static void _SMP_Wait_for_start_multitasking( Per_CPU_Control *cpu_self )
+{
+  unsigned int ready;
+
+  do {
+    _SMP_Try_to_process_message(
+      cpu_self,
+      _Atomic_Load_ulong( &cpu_self->message, ATOMIC_ORDER_RELAXED )
+    );
+    ready = _Atomic_Load_uint(
+      &_SMP_Ready_to_start_multitasking,
+      ATOMIC_ORDER_ACQUIRE
+    );
+  } while ( ready == 0U );
+}
+
 void _SMP_Start_multitasking_on_secondary_processor(
   Per_CPU_Control *cpu_self
 )
@@ -199,28 +243,96 @@ void _SMP_Start_multitasking_on_secondary_processor(
     _SMP_Fatal( SMP_FATAL_MULTITASKING_START_ON_UNASSIGNED_PROCESSOR );
   }
 
-  _Per_CPU_State_change( cpu_self, PER_CPU_STATE_READY_TO_START_MULTITASKING );
-
+  _Per_CPU_Set_state( cpu_self, PER_CPU_STATE_READY_TO_START_MULTITASKING );
+  _SMP_Wait_for_start_multitasking( cpu_self );
   _Thread_Start_multitasking();
 }
 
 void _SMP_Request_shutdown( void )
 {
   ISR_Level level;
+  uint32_t  cpu_max;
+  uint32_t  cpu_index_self;
+  uint32_t  cpu_index;
 
   _ISR_Local_disable( level );
   (void) level;
 
-  _Per_CPU_State_change( _Per_CPU_Get(), PER_CPU_STATE_SHUTDOWN );
+  cpu_max = _SMP_Processor_configured_maximum;
+  cpu_index_self = _SMP_Get_current_processor();
+
+  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
+    Per_CPU_Control *cpu;
+
+    cpu = _Per_CPU_Get_by_index( cpu_index );
+
+    if ( cpu_index == cpu_index_self ) {
+      _Per_CPU_Set_state( cpu, PER_CPU_STATE_SHUTDOWN );
+    } else {
+      _Atomic_Fetch_or_ulong(
+        &cpu->message,
+        SMP_MESSAGE_SHUTDOWN,
+        ATOMIC_ORDER_RELEASE
+      );
+
+      if ( _Per_CPU_Get_state( cpu ) == PER_CPU_STATE_UP ) {
+        _CPU_SMP_Send_interrupt( cpu_index );
+      }
+    }
+  }
+}
+
+long unsigned _SMP_Process_message(
+  Per_CPU_Control *cpu_self,
+  long unsigned    message
+)
+{
+  if ( ( message & SMP_MESSAGE_SHUTDOWN ) != 0 ) {
+    /* Check the state to prevent recursive shutdowns */
+    if ( _Per_CPU_Get_state( cpu_self ) != PER_CPU_STATE_SHUTDOWN ) {
+      _Per_CPU_Set_state( cpu_self, PER_CPU_STATE_SHUTDOWN );
+      _SMP_Fatal( SMP_FATAL_SHUTDOWN_RESPONSE );
+    }
+  }
+
+  if ( ( message & SMP_MESSAGE_PERFORM_JOBS ) != 0 ) {
+    _Per_CPU_Perform_jobs( cpu_self );
+  }
+}
+
+void _SMP_Try_to_process_message(
+  Per_CPU_Control *cpu_self,
+  unsigned long    message
+)
+{
+  if ( message != 0 ) {
+    /*
+     * Fetch the current message.  Only a read-modify-write operation
+     * guarantees that we get an up to date message.  This is especially
+     * important if the function was called using SMP_MESSAGE_FORCE_PROCESSING.
+     */
+    message = _Atomic_Exchange_ulong(
+      &cpu_self->message,
+      0,
+      ATOMIC_ORDER_ACQUIRE
+    );
+
+    _SMP_Process_message( cpu_self, message );
+  }
 }
 
 void _SMP_Send_message( uint32_t cpu_index, unsigned long message )
 {
   Per_CPU_Control *cpu = _Per_CPU_Get_by_index( cpu_index );
 
-  _Atomic_Fetch_or_ulong( &cpu->message, message, ATOMIC_ORDER_RELEASE );
+  (void) _Atomic_Fetch_or_ulong(
+    &cpu->message, message,
+    ATOMIC_ORDER_RELEASE
+  );
 
-  _CPU_SMP_Send_interrupt( cpu_index );
+  if ( _Per_CPU_Get_state( cpu ) == PER_CPU_STATE_UP ) {
+    _CPU_SMP_Send_interrupt( cpu_index );
+  }
 }
 
 void _SMP_Send_message_broadcast( unsigned long message )
diff --git a/cpukit/score/src/smpmulticastaction.c b/cpukit/score/src/smpmulticastaction.c
index 5d65ef14ca..8dbdef80c7 100644
--- a/cpukit/score/src/smpmulticastaction.c
+++ b/cpukit/score/src/smpmulticastaction.c
@@ -92,27 +92,6 @@ void _Per_CPU_Add_job( Per_CPU_Control *cpu, Per_CPU_Job *job )
   _Per_CPU_Jobs_release_and_ISR_enable( cpu, &lock_context );
 }
 
-static void _Per_CPU_Try_perform_jobs( Per_CPU_Control *cpu_self )
-{
-  unsigned long message;
-
-  message = _Atomic_Load_ulong( &cpu_self->message, ATOMIC_ORDER_RELAXED );
-
-  if ( ( message & SMP_MESSAGE_PERFORM_JOBS ) != 0 ) {
-    bool success;
-
-    success = _Atomic_Compare_exchange_ulong(
-      &cpu_self->message, &message,
-      message & ~SMP_MESSAGE_PERFORM_JOBS, ATOMIC_ORDER_RELAXED,
-      ATOMIC_ORDER_RELAXED
-    );
-
-    if ( success ) {
-      _Per_CPU_Perform_jobs( cpu_self );
-    }
-  }
-}
-
 void _Per_CPU_Wait_for_job(
   const Per_CPU_Control *cpu,
   const Per_CPU_Job     *job
@@ -122,17 +101,22 @@ void _Per_CPU_Wait_for_job(
     _Atomic_Load_ulong( &job->done, ATOMIC_ORDER_ACQUIRE )
       != PER_CPU_JOB_DONE
   ) {
+    Per_CPU_Control *cpu_self;
+
     switch ( _Per_CPU_Get_state( cpu ) ) {
       case PER_CPU_STATE_INITIAL:
       case PER_CPU_STATE_READY_TO_START_MULTITASKING:
-      case PER_CPU_STATE_REQUEST_START_MULTITASKING:
       case PER_CPU_STATE_UP:
         /*
-         * Calling this function with the current processor is intentional.
-         * We have to perform our own jobs here in case inter-processor
-         * interrupts are not working.
+         * Calling this function with the current processor is intentional.  We
+         * have to perform our own jobs here in case inter-processor interrupts
+         * are not working.
          */
-        _Per_CPU_Try_perform_jobs( _Per_CPU_Get() );
+        cpu_self = _Per_CPU_Get();
+        _SMP_Try_to_process_message(
+          cpu_self,
+          _Atomic_Load_ulong( &cpu_self->message, ATOMIC_ORDER_RELAXED )
+        );
         break;
       default:
         _SMP_Fatal( SMP_FATAL_WRONG_CPU_STATE_TO_PERFORM_JOBS );
diff --git a/cpukit/score/src/threadstartmultitasking.c b/cpukit/score/src/threadstartmultitasking.c
index 094a535394..9fa52a58ac 100644
--- a/cpukit/score/src/threadstartmultitasking.c
+++ b/cpukit/score/src/threadstartmultitasking.c
@@ -22,6 +22,7 @@
 
 #include <rtems/score/threadimpl.h>
 #include <rtems/score/assert.h>
+#include <rtems/score/smpimpl.h>
 
 void _Thread_Start_multitasking( void )
 {
@@ -29,7 +30,8 @@ void _Thread_Start_multitasking( void )
   Thread_Control  *heir;
 
 #if defined(RTEMS_SMP)
-  _Per_CPU_State_change( cpu_self, PER_CPU_STATE_UP );
+  _Per_CPU_Set_state( cpu_self, PER_CPU_STATE_UP );
+  _SMP_Try_to_process_message( cpu_self, SMP_MESSAGE_FORCE_PROCESSING );
 
   /*
    * Threads begin execution in the _Thread_Handler() function.   This