bugfix: Setting OMPI_MPI_THREAD_LEVEL to a value different than requested crashes

ompi/mpi/c/init.c.in

@@ -15,6 +15,7 @@
  *                         and Technology (RIST). All rights reserved.
  * Copyright (c) 2024      Triad National Security, LLC. All rights
  *                         reserved.
+ * Copyright (c) 2025      Advanced Micro Devices, Inc. All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -37,18 +38,13 @@ PROTOTYPE INT init(INT_OUT argc, ARGV argv)
 {
     int err;
     int provided;
-    char *env;
     int required = MPI_THREAD_SINGLE;
 
     /* check for environment overrides for required thread level.  If
        there is, check to see that it is a valid/supported thread level.
        If not, default to MPI_THREAD_MULTIPLE. */
-
-    if (NULL != (env = getenv("OMPI_MPI_THREAD_LEVEL"))) {
-        required = atoi(env);
-        if (required < MPI_THREAD_SINGLE || required > MPI_THREAD_MULTIPLE) {
-            required = MPI_THREAD_MULTIPLE;
-        }
+    if (OMPI_SUCCESS > ompi_getenv_mpi_thread_level(&required)) {
+        required = MPI_THREAD_MULTIPLE;
     }
 
     /* Call the back-end initialization function (we need to put as

ompi/mpi/c/init_thread.c.in

@@ -18,6 +18,7 @@
  *                         reserved.
  * Copyright (c) 2024      Triad National Security, LLC. All rights
  *                         reserved.
+ * Copyright (c) 2025      Advanced Micro Devices, Inc. All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -40,24 +41,29 @@ PROTOTYPE ERROR_CLASS init_thread(INT_OUT argc, ARGV argv, INT required,
                                   INT_OUT provided)
 {
     int err, safe_required = MPI_THREAD_SERIALIZED;
-    char *env;
+    bool err_arg_required = false;
 
     ompi_hook_base_mpi_init_thread_top(argc, argv, required, provided);
 
     /* Detect an incorrect thread support level, but dont report until we have the minimum
      * infrastructure setup.
+     * In the future integer MPI_ABI values for MPI_THREAD_SINGLE-MULTIPLE
+     * may have gaps between them, so just checking the range is not enough.
      */
-    if( (MPI_THREAD_SINGLE == required) || (MPI_THREAD_SERIALIZED == required) ||
-        (MPI_THREAD_FUNNELED == required) || (MPI_THREAD_MULTIPLE == required) ) {
-
-        if (NULL != (env = getenv("OMPI_MPI_THREAD_LEVEL")))  {
-            safe_required = atoi(env);
-        }
-        else {
-            safe_required = required;
-        }
+    err_arg_required = (required != MPI_THREAD_SINGLE && required != MPI_THREAD_FUNNELED &&
+                        required != MPI_THREAD_SERIALIZED && required != MPI_THREAD_MULTIPLE);
+    if (!err_arg_required) {
+        safe_required = required;
     }
 
+    /* check for environment overrides for required thread level. If
+     * there is, check to see that it is a valid/supported thread level.
+     * If valid, the environment variable always override the provided thread
+     * level (even if lower than argument `required`). A user program can
+     * check `provided != required` to check if `required` has been overruled.
+     */
+    err_arg_required |= (OMPI_SUCCESS > ompi_getenv_mpi_thread_level(&safe_required));
+
     *provided = safe_required;
 
     /* Call the back-end initialization function (we need to put as
@@ -70,7 +76,7 @@ PROTOTYPE ERROR_CLASS init_thread(INT_OUT argc, ARGV argv, INT required,
         err = ompi_mpi_init(0, NULL, safe_required, provided, false);
     }
 
-    if( safe_required != required ) {
+    if (err_arg_required) {
         /* Trigger the error handler for the incorrect argument. Keep it separate from the
          * check on the ompi_mpi_init return and report a nice, meaningful error message to
          * the user. */

ompi/runtime/mpiruntime.h

@@ -16,6 +16,7 @@
  * Copyright (c) 2009      University of Houston.  All rights reserved.
  * Copyright (c) 2014      Intel, Inc. All rights reserved.
  * Copyright (c) 2018      FUJITSU LIMITED.  All rights reserved.
+ * Copyright (c) 2025      Advanced Micro Devices, Inc. All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -163,6 +164,27 @@ extern opal_hash_table_t ompi_mpi_f90_complex_hashtable;
 /** version string of ompi */
 OMPI_DECLSPEC extern const char ompi_version_string[];
 
+/**
+ * Obtain the required thread level from environment (if any)
+ *
+ * @param requested Thread support that is requested (OUT)
+ *
+ * @returns Error code if environment exist but has an invalid value
+ *
+ * The function reads the environment variable OMPI_MPI_THREAD_LEVEL
+ * and set parameter requested accordingly. If the environment is not
+ * set, or has an invalid value, requested is left unchanged.
+ */
+int ompi_getenv_mpi_thread_level(int *requested);
+
+/**
+ * Determine the thread level
+ *
+ * @param requested Thread support that is requested (IN)
+ * @param provided Thread support that is provided (OUT)
+ */
+void ompi_mpi_thread_level(int requested, int *provided);
+
 /**
  * Determine the thread level
  *

ompi/runtime/ompi_mpi_init.c

@@ -29,6 +29,7 @@
  * Copyright (c) 2021      Nanook Consulting.  All rights reserved.
  * Copyright (c) 2021-2022 Triad National Security, LLC. All rights
  *                         reserved.
+ * Copyright (c) 2025      Advanced Micro Devices, Inc. All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -268,6 +269,42 @@ MPI_Fint *MPI_F08_STATUSES_IGNORE = NULL;
 
 #include "mpif-c-constants.h"
 
+int ompi_getenv_mpi_thread_level(int *requested)
+{
+    char* env;
+    if (NULL != (env = getenv("OMPI_MPI_THREAD_LEVEL"))) {
+        /* deal with string values, int values (no atoi, it doesn't error check) */
+        /* In the future integer MPI_ABI values for MPI_THREAD_SINGLE-MULTIPLE
+         * may be non-sequential (but ordered) integer values.
+         * If you are implementing MPI ABI changes please refer to
+         * https://github.com/open-mpi/ompi/pull/13211#discussion_r2085086844
+         */
+        if (0 == strcasecmp(env, "multiple") ||
+            0 == strcasecmp(env, "MPI_THREAD_MULTIPLE") ||
+            0 == strcmp(env, "3")) {
+            return *requested = MPI_THREAD_MULTIPLE;
+        }
+        if (0 == strcasecmp(env, "serialized") ||
+            0 == strcasecmp(env, "MPI_THREAD_SERIALIZED") ||
+            0 == strcmp(env, "2")) {
+            return *requested = MPI_THREAD_SERIALIZED;
+        }
+        if (0 == strcasecmp(env, "funneled") ||
+            0 == strcasecmp(env, "MPI_THREAD_FUNNELED") ||
+            0 == strcmp(env, "1")) {
+            return *requested = MPI_THREAD_FUNNELED;
+        }
+        if (0 == strcasecmp(env, "single") ||
+            0 == strcasecmp(env, "MPI_THREAD_SINGLE") ||
+            0 == strcmp(env, "0")) {
+            return *requested = MPI_THREAD_SINGLE;
+        }
+        /* the env value is invalid... */
+        return OMPI_ERR_BAD_PARAM;
+    }
+    return OMPI_SUCCESS;
+}
+
 void ompi_mpi_thread_level(int requested, int *provided)
 {
     /**