Fix corner case involving threads and CUDA-aware support.

This commit was SVN r29579.

ompi/mca/common/cuda/common_cuda.c

@@ -1475,6 +1475,7 @@ static int mca_common_cuda_is_gpu_buffer(const void *pUserBuf)
     int res;
     CUmemorytype memType;
     CUdeviceptr dbuf = (CUdeviceptr)pUserBuf;
+    CUcontext ctx = NULL;
 
     res = cuFunc.cuPointerGetAttribute(&memType,
                                        CU_POINTER_ATTRIBUTE_MEMORY_TYPE, dbuf);
@@ -1489,6 +1490,42 @@ static int mca_common_cuda_is_gpu_buffer(const void *pUserBuf)
     /* Must be a device pointer */
     assert(memType == CU_MEMORYTYPE_DEVICE);
 
+    /* This piece of code was added in to handle in a case involving
+     * OMP threads.  The user had initialized CUDA and then spawned
+     * two threads.  The first thread had the CUDA context, but the
+     * second thread did not.  We therefore had no context to act upon
+     * and future CUDA driver calls would fail.  Therefore, if we have
+     * GPU memory, but no context, get the context from the GPU memory
+     * and set the current context to that.  It is rare that we will not
+     * have a context. */
+    res = cuFunc.cuCtxGetCurrent(&ctx);
+    if (OPAL_UNLIKELY(NULL == ctx)) {
+        if (CUDA_SUCCESS == res) {
+            res = cuFunc.cuPointerGetAttribute(&ctx,
+                                               CU_POINTER_ATTRIBUTE_CONTEXT, dbuf);
+            if (res != CUDA_SUCCESS) {
+                opal_output(0, "CUDA: error calling cuPointerGetAttribute: "
+                            "res=%d, ptr=%p aborting...", res, pUserBuf);
+                ompi_rte_abort(1, NULL);
+            } else {
+                res = cuCtxSetCurrent(ctx);
+                if (res != CUDA_SUCCESS) {
+                    opal_output(0, "CUDA: error calling cuCtxSetCurrent: "
+                                "res=%d, ptr=%p aborting...", res, pUserBuf);
+                    ompi_rte_abort(1, NULL);
+                } else {
+                    opal_output_verbose(10, mca_common_cuda_output,
+                                        "CUDA: cuCtxSetCurrent passed: ptr=%p", pUserBuf);
+                }
+            }
+        } else {
+            /* Print error and proceed */
+            opal_output(0, "CUDA: error calling cuCtxGetCurrent: "
+                        "res=%d, ptr=%p aborting...", res, pUserBuf);
+            ompi_rte_abort(1, NULL);
+        }
+    }
+
     /* First access on a device pointer finalizes CUDA support initialization.
      * If initialization fails, disable support. */
     if (!stage_three_init_complete) {