[Openmp-commits] [openmp] 3895148 - [OpenMP] Fix a race in task queue reallocation

[Joachim Protze via Openmp-commits]

Author: Joachim Protze
Date: 2020-05-25T10:23:22+02:00
New Revision: 3895148d7cd8ff76220f8f8209ec06369a8e816f

URL: https://github.com/llvm/llvm-project/commit/3895148d7cd8ff76220f8f8209ec06369a8e816f
DIFF: https://github.com/llvm/llvm-project/commit/3895148d7cd8ff76220f8f8209ec06369a8e816f.diff

LOG: [OpenMP] Fix a race in task queue reallocation

__kmp_realloc_task_deque implicitly assumes, that the task queue is full
(ntasks == size), therefore tail = size in line 319.
An assertion is added to document this assumption.

The first check for a full queue is before the locking and might not hold
when the lock is taken. So, we need to check again for this condition when
we have the lock.

Reviewed By: AndreyChurbanov

Differential Revision: https://reviews.llvm.org/D80480

Added: 
    

Modified: 
    openmp/runtime/src/kmp_tasking.cpp

Removed: 
    


################################################################################
diff  --git a/openmp/runtime/src/kmp_tasking.cpp b/openmp/runtime/src/kmp_tasking.cpp
index c92851741060..6e584731a85f 100644
--- a/openmp/runtime/src/kmp_tasking.cpp
+++ b/openmp/runtime/src/kmp_tasking.cpp
@@ -298,6 +298,7 @@ static bool __kmp_task_is_allowed(int gtid, const kmp_int32 is_constrained,
 static void __kmp_realloc_task_deque(kmp_info_t *thread,
                                      kmp_thread_data_t *thread_data) {
   kmp_int32 size = TASK_DEQUE_SIZE(thread_data->td);
+  KMP_DEBUG_ASSERT(TCR_4(thread_data->td.td_deque_ntasks) == size);
   kmp_int32 new_size = 2 * size;
 
   KE_TRACE(10, ("__kmp_realloc_task_deque: T#%d reallocating deque[from %d to "
@@ -381,8 +382,11 @@ static kmp_int32 __kmp_push_task(kmp_int32 gtid, kmp_task_t *task) {
     } else {
       __kmp_acquire_bootstrap_lock(&thread_data->td.td_deque_lock);
       locked = 1;
-      // expand deque to push the task which is not allowed to execute
-      __kmp_realloc_task_deque(thread, thread_data);
+      if (TCR_4(thread_data->td.td_deque_ntasks) >=
+          TASK_DEQUE_SIZE(thread_data->td)) {
+        // expand deque to push the task which is not allowed to execute
+        __kmp_realloc_task_deque(thread, thread_data);
+      }
     }
   }
   // Lock the deque for the task push operation
@@ -3659,7 +3663,11 @@ static bool __kmp_give_task(kmp_info_t *thread, kmp_int32 tid, kmp_task_t *task,
       return result;
 
     __kmp_acquire_bootstrap_lock(&thread_data->td.td_deque_lock);
-    __kmp_realloc_task_deque(thread, thread_data);
+    if (TCR_4(thread_data->td.td_deque_ntasks) >=
+        TASK_DEQUE_SIZE(thread_data->td)) {
+      // expand deque to push the task which is not allowed to execute
+      __kmp_realloc_task_deque(thread, thread_data);
+    }
 
   } else {