Don't overwrite blas_thread_buffer if already set

After a fork it is possible that blas_thread_buffer has already
allocated memory buffers: goto_set_num_threads does allocate those
already and it may be called by num_cpu_avail in case the OpenBLAS
NUM_THREADS differ from the OMP num threads.
This leads to a memory leak which can cause subsequent execution of BLAS
kernels to fail.

Fixes #2993

driver/others/blas_server_omp.c

@@ -76,10 +76,28 @@ static atomic_bool blas_buffer_inuse[MAX_PARALLEL_NUMBER];
 static _Bool blas_buffer_inuse[MAX_PARALLEL_NUMBER];
 #endif
 
-void goto_set_num_threads(int num_threads) {
+static void adjust_thread_buffers() {
 
   int i=0, j=0;
 
+  //adjust buffer for each thread
+  for(i=0; i < MAX_PARALLEL_NUMBER; i++) {
+    for(j=0; j < blas_cpu_number; j++){
+      if(blas_thread_buffer[i][j] == NULL){
+        blas_thread_buffer[i][j] = blas_memory_alloc(2);
+      }
+    }
+    for(; j < MAX_CPU_NUMBER; j++){
+      if(blas_thread_buffer[i][j] != NULL){
+        blas_memory_free(blas_thread_buffer[i][j]);
+        blas_thread_buffer[i][j] = NULL;
+      }
+    }
+  }
+}
+
+void goto_set_num_threads(int num_threads) {
+
   if (num_threads < 1) num_threads = blas_num_threads;
 
   if (num_threads > MAX_CPU_NUMBER) num_threads = MAX_CPU_NUMBER;
@@ -92,20 +110,7 @@ void goto_set_num_threads(int num_threads) {
 
   omp_set_num_threads(blas_cpu_number);
 
-  //adjust buffer for each thread
-  for(i=0; i<MAX_PARALLEL_NUMBER; i++) {
-    for(j=0; j<blas_cpu_number; j++){
-      if(blas_thread_buffer[i][j]==NULL){
-        blas_thread_buffer[i][j]=blas_memory_alloc(2);
-      }
-    }
-    for(; j<MAX_CPU_NUMBER; j++){
-      if(blas_thread_buffer[i][j]!=NULL){
-        blas_memory_free(blas_thread_buffer[i][j]);
-        blas_thread_buffer[i][j]=NULL;
-      }
-    }
-  }
+  adjust_thread_buffers();
 #if defined(ARCH_MIPS64)
   //set parameters for different number of threads.
   blas_set_parameter();
@@ -119,20 +124,11 @@ void openblas_set_num_threads(int num_threads) {
 
 int blas_thread_init(void){
 
-  int i=0, j=0;
-
   blas_get_cpu_number();
 
-  blas_server_avail = 1;
+  adjust_thread_buffers();
 
-  for(i=0; i<MAX_PARALLEL_NUMBER; i++) {
-    for(j=0; j<blas_num_threads; j++){
-      blas_thread_buffer[i][j]=blas_memory_alloc(2);
-    }
-    for(; j<MAX_CPU_NUMBER; j++){
-      blas_thread_buffer[i][j]=NULL;
-    }
-  }
+  blas_server_avail = 1;
 
   return 0;
 }