test-rcu-list: access n_reclaims and n_nodes_removed with atomic64

To avoid undefined behaviour.

Note that these "atomics" are atomic in the "access once" sense.
The variables are updated by a single thread at a time, so no
"full" atomics are necessary.
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <20180910232752.31565-6-cota@braap.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tests/test-rcu-list.c

@@ -33,8 +33,8 @@
 static QemuMutex counts_mutex;
 static long long n_reads = 0LL;
 static long long n_updates = 0LL;
-static long long n_reclaims = 0LL;
-static long long n_nodes_removed = 0LL;
+static int64_t n_reclaims;
+static int64_t n_nodes_removed;
 static long long n_nodes = 0LL;
 static int g_test_in_charge = 0;
 
@@ -104,7 +104,7 @@ static void reclaim_list_el(struct rcu_head *prcu)
     struct list_element *el = container_of(prcu, struct list_element, rcu);
     g_free(el);
     /* Accessed only from call_rcu thread.  */
-    n_reclaims++;
+    atomic_set_i64(&n_reclaims, n_reclaims + 1);
 }
 
 #if TEST_LIST_TYPE == 1
@@ -232,7 +232,7 @@ static void *rcu_q_updater(void *arg)
     qemu_mutex_lock(&counts_mutex);
     n_nodes += n_nodes_local;
     n_updates += n_updates_local;
-    n_nodes_removed += n_removed_local;
+    atomic_set_i64(&n_nodes_removed, n_nodes_removed + n_removed_local);
     qemu_mutex_unlock(&counts_mutex);
     return NULL;
 }
@@ -286,19 +286,21 @@ static void rcu_qtest(const char *test, int duration, int nreaders)
         n_removed_local++;
     }
     qemu_mutex_lock(&counts_mutex);
-    n_nodes_removed += n_removed_local;
+    atomic_set_i64(&n_nodes_removed, n_nodes_removed + n_removed_local);
     qemu_mutex_unlock(&counts_mutex);
     synchronize_rcu();
-    while (n_nodes_removed > n_reclaims) {
+    while (atomic_read_i64(&n_nodes_removed) > atomic_read_i64(&n_reclaims)) {
         g_usleep(100);
         synchronize_rcu();
     }
     if (g_test_in_charge) {
-        g_assert_cmpint(n_nodes_removed, ==, n_reclaims);
+        g_assert_cmpint(atomic_read_i64(&n_nodes_removed), ==,
+                        atomic_read_i64(&n_reclaims));
     } else {
         printf("%s: %d readers; 1 updater; nodes read: "  \
-               "%lld, nodes removed: %lld; nodes reclaimed: %lld\n",
-               test, nthreadsrunning - 1, n_reads, n_nodes_removed, n_reclaims);
+               "%lld, nodes removed: %"PRIi64"; nodes reclaimed: %"PRIi64"\n",
+               test, nthreadsrunning - 1, n_reads,
+               atomic_read_i64(&n_nodes_removed), atomic_read_i64(&n_reclaims));
         exit(0);
     }
 }