From d9ccaa8ddbb76b17e7674d58a88feb9fcfa3bac5 Mon Sep 17 00:00:00 2001
From: Neil Horman <nhorman@openssl.org>
Date: Mon, 25 Mar 2024 13:35:05 -0400
Subject: [PATCH] Add code to check wrapping

---
 test/threadstest.c | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/test/threadstest.c b/test/threadstest.c
index c27f51f85dcf0c..1f1972b129f49a 100644
--- a/test/threadstest.c
+++ b/test/threadstest.c
@@ -351,6 +351,9 @@ static void writer2_fn(void)
     CRYPTO_atomic_add(&writer2_done, 1, &local, NULL);
 }
 
+#define NO_WRAP 0
+#define WRAPPED_LAST_ITER 1
+#define BETTER_NOT_WRAP 2
 static void reader_fn(int *iterations)
 {
     unsigned int count = 0;
@@ -360,6 +363,7 @@ static void reader_fn(int *iterations)
     int lw1 = 0;
     int lw2 = 0;
     size_t i;
+    int wrap = NO_WRAP;
 
     while (lw1 != 1 || lw2 != 1) {
         CRYPTO_atomic_add(&writer1_done, 0, &lw1, NULL);
@@ -368,13 +372,39 @@ static void reader_fn(int *iterations)
         ossl_rcu_read_lock(rcu_lock);
         valp = ossl_rcu_deref(&writer_ptr);
         val = (valp == NULL) ? 0 : *valp;
-        if (oldval > val) {
-            TEST_info("rcu torture value went backwards! %llu : %llu", (unsigned long long)oldval, (unsigned long long)val);
-            TEST_info("val ptr is %p\n", (void*)valp);
-            for (i=0; i<256; i++) {
-                TEST_info("Old Addrs for write %zu\n is %p\n", i, old_addrs[i]);
+
+        /*
+         * If we didn't wrap before, and we see a wrap
+         * condition, mark it as such
+         */
+        if (oldval > val && wrap == NO_WRAP) {
+           wrap = WRAPPED_LAST_ITER;
+        }
+
+        /*
+         * If this iteration wrapped, indicate that
+         * its ok, but we better not wrap again
+         */
+        if (wrap == WRAPPED_LAST_ITER) {
+            wrap = BETTER_NOT_WRAP;
+        } else {
+            /*
+             * We get here if we've wrapped once, but we better not go
+             * backwards again
+             */
+            if (oldval > val) {
+                TEST_info("rcu torture value went backwards! %llu : %llu", (unsigned long long)oldval, (unsigned long long)val);
+                TEST_info("val ptr is %p\n", (void*)valp);
+                for (i=0; i<256; i++) {
+                    TEST_info("Old Addrs for write %zu\n is %p\n", i, old_addrs[i]);
+                }
+                rcu_torture_result = 0;
+            } else {
+                /*
+                 * If we get here, we've successfully wrapped, and can continue
+                 */
+                wrap = NO_WRAP;
             }
-            rcu_torture_result = 0;
         }
         oldval = val; /* just try to deref the pointer */
         ossl_rcu_read_unlock(rcu_lock);