2 files changed, 24 insertions, 2 deletions

diff --git a/cpukit/rtems/src/regiongetsegment.c b/cpukit/rtems/src/regiongetsegment.c
index 27d6bf66dd..dc58a27ff3 100644
--- a/cpukit/rtems/src/regiongetsegment.c
+++ b/cpukit/rtems/src/regiongetsegment.c
@@ -98,6 +98,14 @@ rtems_status_code rtems_region_get_segment(
         return RTEMS_UNSATISFIED;
       }
 
+      /*
+       *  Switch from using the memory allocation mutex to using a
+       *  dispatching disabled critical section.  We have to do this
+       *  because this thread is going to block.
+       */
+      _Thread_Disable_dispatch();
+      _RTEMS_Unlock_allocator();
+
       executing->Wait.queue           = &the_region->Wait_queue;
       executing->Wait.id              = id;
       executing->Wait.count           = size;
@@ -107,7 +115,8 @@ rtems_status_code rtems_region_get_segment(
 
       _Thread_queue_Enqueue( &the_region->Wait_queue, timeout );
 
-      _RTEMS_Unlock_allocator();
+      _Thread_Enable_dispatch();
+
       return (rtems_status_code) executing->Wait.return_code;
   }
 
diff --git a/cpukit/rtems/src/regionreturnsegment.c b/cpukit/rtems/src/regionreturnsegment.c
index 74517c0812..79d33b3828 100644
--- a/cpukit/rtems/src/regionreturnsegment.c
+++ b/cpukit/rtems/src/regionreturnsegment.c
@@ -94,6 +94,19 @@ rtems_status_code rtems_region_return_segment(
       }
 
       the_region->number_of_used_blocks -= 1;
+
+      /*
+       *  Switch from using the memory allocation mutex to using a
+       *  dispatching disabled critical section.  We have to do this
+       *  because this thread may unblock one or more threads that were
+       *  waiting on memory.
+       *
+       *  NOTE: The following loop is O(n) where n is the number of
+       *        threads whose memory request is satisfied.
+       */
+      _RTEMS_Unlock_allocator();
+      _Thread_Disable_dispatch();
+
       for ( ; ; ) {
         the_thread = _Thread_queue_First( &the_region->Wait_queue );
 
@@ -113,8 +126,8 @@ rtems_status_code rtems_region_return_segment(
         _Thread_queue_Extract( &the_region->Wait_queue, the_thread );
         the_thread->Wait.return_code = RTEMS_SUCCESSFUL;
       }
+      _Thread_Enable_dispatch();
 
-      _RTEMS_Unlock_allocator();
       return RTEMS_SUCCESSFUL;
   }