test-coroutine: Add rwlock upgrade test

Test that rwlock upgrade is fair, and that readers go back to sleep if
a writer is in line.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20210325112941.365238-6-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/unit/test-coroutine.c

@@ -264,6 +264,67 @@ static void test_co_mutex_lockable(void)
     g_assert(QEMU_MAKE_LOCKABLE(null_pointer) == NULL);
 }
 
+static CoRwlock rwlock;
+
+/* Test that readers are properly sent back to the queue when upgrading,
+ * even if they are the sole readers.  The test scenario is as follows:
+ *
+ *
+ * | c1           | c2         |
+ * |--------------+------------+
+ * | rdlock       |            |
+ * | yield        |            |
+ * |              | wrlock     |
+ * |              | <queued>   |
+ * | upgrade      |            |
+ * | <queued>     | <dequeued> |
+ * |              | unlock     |
+ * | <dequeued>   |            |
+ * | unlock       |            |
+ */
+
+static void coroutine_fn rwlock_yield_upgrade(void *opaque)
+{
+    qemu_co_rwlock_rdlock(&rwlock);
+    qemu_coroutine_yield();
+
+    qemu_co_rwlock_upgrade(&rwlock);
+    qemu_co_rwlock_unlock(&rwlock);
+
+    *(bool *)opaque = true;
+}
+
+static void coroutine_fn rwlock_wrlock_yield(void *opaque)
+{
+    qemu_co_rwlock_wrlock(&rwlock);
+    qemu_coroutine_yield();
+
+    qemu_co_rwlock_unlock(&rwlock);
+    *(bool *)opaque = true;
+}
+
+static void test_co_rwlock_upgrade(void)
+{
+    bool c1_done = false;
+    bool c2_done = false;
+    Coroutine *c1, *c2;
+
+    qemu_co_rwlock_init(&rwlock);
+    c1 = qemu_coroutine_create(rwlock_yield_upgrade, &c1_done);
+    c2 = qemu_coroutine_create(rwlock_wrlock_yield, &c2_done);
+
+    qemu_coroutine_enter(c1);
+    qemu_coroutine_enter(c2);
+
+    /* c1 now should go to sleep.  */
+    qemu_coroutine_enter(c1);
+    g_assert(!c1_done);
+
+    qemu_coroutine_enter(c2);
+    g_assert(c1_done);
+    g_assert(c2_done);
+}
+
 /*
  * Check that creation, enter, and return work
  */
@@ -501,6 +562,7 @@ int main(int argc, char **argv)
     g_test_add_func("/basic/order", test_order);
     g_test_add_func("/locking/co-mutex", test_co_mutex);
     g_test_add_func("/locking/co-mutex/lockable", test_co_mutex_lockable);
+    g_test_add_func("/locking/co-rwlock/upgrade", test_co_rwlock_upgrade);
     if (g_test_perf()) {
         g_test_add_func("/perf/lifecycle", perf_lifecycle);
         g_test_add_func("/perf/nesting", perf_nesting);