__kmp_free_task: Fix for serial explicit tasks producing proxy tasks

Consider the following code which may be executed by a serial team:

    int dep;
    #pragma omp target nowait depend(out: dep)
    {
        sleep(1);
    }
    #pragma omp task depend(in: dep)
    {
        #pragma omp target nowait
        {
            sleep(1);
        }
    }

Here the explicit task may not be freed until the nested proxy task has
finished. The current code hasn't considered this and called __kmp_free_task
anyway which triggered an assert because of remaining incomplete children:

    KMP_DEBUG_ASSERT( TCR_4(taskdata->td_incomplete_child_tasks) == 0 );

Differential Revision: https://reviews.llvm.org/D23115

llvm-svn: 277991

1 files changed, 10 insertions, 14 deletions

diff --git a/openmp/runtime/src/kmp_tasking.c b/openmp/runtime/src/kmp_tasking.c
index ce1b63d5cd9..ac9a25f3dde 100644
--- a/openmp/runtime/src/kmp_tasking.c
+++ b/openmp/runtime/src/kmp_tasking.c
@@ -576,15 +576,13 @@ __kmp_free_task( kmp_int32 gtid, kmp_taskdata_t * taskdata, kmp_info_t * thread
 static void
 __kmp_free_task_and_ancestors( kmp_int32 gtid, kmp_taskdata_t * taskdata, kmp_info_t * thread )
 {
-    kmp_int32 children = 0;
-    kmp_int32 team_or_tasking_serialized = taskdata -> td_flags.team_serial || taskdata -> td_flags.tasking_ser;
-
+    // Proxy tasks must always be allowed to free their parents
+    // because they can be run in background even in serial mode.
+    kmp_int32 task_serial = taskdata->td_flags.task_serial && !taskdata->td_flags.proxy;
     KMP_DEBUG_ASSERT( taskdata -> td_flags.tasktype == TASK_EXPLICIT );
 
-    if ( !team_or_tasking_serialized ) {
-        children = KMP_TEST_THEN_DEC32( (kmp_int32 *)(& taskdata -> td_allocated_child_tasks) ) - 1;
-        KMP_DEBUG_ASSERT( children >= 0 );
-    }
+    kmp_int32 children = KMP_TEST_THEN_DEC32( (kmp_int32 *)(& taskdata -> td_allocated_child_tasks) ) - 1;
+    KMP_DEBUG_ASSERT( children >= 0 );
 
     // Now, go up the ancestor tree to see if any ancestors can now be freed.
     while ( children == 0 )
@@ -599,16 +597,14 @@ __kmp_free_task_and_ancestors( kmp_int32 gtid, kmp_taskdata_t * taskdata, kmp_in
 
         taskdata = parent_taskdata;
 
-        // Stop checking ancestors at implicit task or if tasking serialized
+        // Stop checking ancestors at implicit task
         // instead of walking up ancestor tree to avoid premature deallocation of ancestors.
-        if ( team_or_tasking_serialized || taskdata -> td_flags.tasktype == TASK_IMPLICIT )
+        if ( task_serial || taskdata -> td_flags.tasktype == TASK_IMPLICIT )
             return;
 
-        if ( !team_or_tasking_serialized ) {
-            // Predecrement simulated by "- 1" calculation
-            children = KMP_TEST_THEN_DEC32( (kmp_int32 *)(& taskdata -> td_allocated_child_tasks) ) - 1;
-            KMP_DEBUG_ASSERT( children >= 0 );
-        }
+        // Predecrement simulated by "- 1" calculation
+        children = KMP_TEST_THEN_DEC32( (kmp_int32 *)(& taskdata -> td_allocated_child_tasks) ) - 1;
+        KMP_DEBUG_ASSERT( children >= 0 );
     }
 
     KA_TRACE(20, ("__kmp_free_task_and_ancestors(exit): T#%d task %p has %d children; "