replay/replay-internal.c: track holding of replay_lock

This is modelled after the iothread mutex lock. We keep a TLS flag to
indicate when that thread has acquired the lock and assert we don't
double-lock or release when we shouldn't have.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20180227095237.1060.44661.stgit@pasha-VirtualBox>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

replay/replay-internal.c

@@ -169,6 +169,8 @@ void replay_finish_event(void)
     replay_fetch_data_kind();
 }
 
+static __thread bool replay_locked;
+
 void replay_mutex_init(void)
 {
     qemu_mutex_init(&lock);
@@ -179,13 +181,22 @@ void replay_mutex_destroy(void)
     qemu_mutex_destroy(&lock);
 }
 
+static bool replay_mutex_locked(void)
+{
+    return replay_locked;
+}
+
 void replay_mutex_lock(void)
 {
+    g_assert(!replay_mutex_locked());
     qemu_mutex_lock(&lock);
+    replay_locked = true;
 }
 
 void replay_mutex_unlock(void)
 {
+    g_assert(replay_mutex_locked());
+    replay_locked = false;
     qemu_mutex_unlock(&lock);
 }