Defang the lhash test

This is bascially eating my mac, as it now runs for 80 seconds
and eats all the CPU's exercising lock contention.

This dials it back to consume at most a quarter of the CPU's in
use by HARNESS_JOBS, unless LHASH_WORKERS is set to override it
in which case we use that.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
(Merged from https://github.com/openssl/openssl/pull/29406)

test/lhash_test.c

@@ -496,7 +496,35 @@ static HT *m_ht = NULL;
 #define NUM_WORKERS 16
 
 static struct test_mt_entry test_mt_entries[TEST_MT_POOL_SZ];
-static char *worker_exits[NUM_WORKERS];
+static char **worker_exits;
+static thread_t *workers;
+static int num_workers = NUM_WORKERS;
+
+static int setup_num_workers(void)
+{
+    char *harness_jobs = getenv("HARNESS_JOBS");
+    char *lhash_workers = getenv("LHASH_WORKERS");
+    /* If we have HARNESS_JOBS set, don't eat more than a quarter */
+    if (harness_jobs != NULL) {
+        int jobs = atoi(harness_jobs);
+        if (jobs > 0)
+            num_workers = jobs / 4;
+    }
+    /* But if we have explicitly set LHASH_WORKERS use that */
+    if (lhash_workers != NULL) {
+        int jobs = atoi(lhash_workers);
+        if (jobs > 0)
+            num_workers = jobs;
+    }
+
+    TEST_info("using %d workers\n", num_workers);
+
+    free(worker_exits);
+    free(workers);
+    worker_exits = calloc(num_workers, sizeof(*worker_exits));
+    workers = calloc(num_workers, sizeof(*workers));
+    return worker_exits != NULL && workers != NULL;
+}
 
 HT_START_KEY_DEFN(mtkey)
 HT_DEF_KEY_FIELD(index, uint32_t)
@@ -686,15 +714,15 @@ static int test_hashtable_multithread(int idx)
         .no_rcu = idx,
     };
     int ret = 0;
-    thread_t workers[NUM_WORKERS];
     int i;
 #ifdef MEASURE_HASH_PERFORMANCE
     struct timeval start, end, delta;
 #endif
 
-    memset(worker_exits, 0, sizeof(char *) * NUM_WORKERS);
+    if (!TEST_true(setup_num_workers()))
+        goto end;
+
     memset(test_mt_entries, 0, sizeof(TEST_MT_ENTRY) * TEST_MT_POOL_SZ);
-    memset(workers, 0, sizeof(thread_t) * NUM_WORKERS);
 
     m_ht = ossl_ht_new(&hash_conf);
 
@@ -711,13 +739,13 @@ static int test_hashtable_multithread(int idx)
     gettimeofday(&start, NULL);
 #endif
 
-    for (i = 0; i < NUM_WORKERS; i++) {
+    for (i = 0; i < num_workers; i++) {
         if (!run_thread(&workers[i], do_mt_hash_work))
             goto shutdown;
     }
 
 shutdown:
-    for (--i; i >= 0; i--) {
+    for (i = 0; i < num_workers; i++) {
         wait_for_thread(workers[i]);
     }
 
@@ -726,7 +754,7 @@ shutdown:
      * conditions
      */
     ret = 1;
-    for (i = 0; i < NUM_WORKERS; i++) {
+    for (i = 0; i < num_workers; i++) {
         if (worker_exits[i] != NULL) {
             TEST_info("Worker %d failed: %s\n", i, worker_exits[i]);
             ret = 0;
@@ -752,6 +780,10 @@ end_free:
     CRYPTO_THREAD_lock_free(worker_lock);
     CRYPTO_THREAD_lock_free(testrand_lock);
     CRYPTO_THREAD_lock_free(no_rcu_lock);
+    free(workers);
+    workers = NULL;
+    free(worker_exits);
+    worker_exits = NULL;
 end:
     return ret;
 }