Fix wake_with()

wake_with(action) was implemented using thread_handle, as the following:

thread_handle h(handle());
action();
h.wake();

This implementation is wrong: It only takes the RCU lock (which prevents
the destruction of _detached_state) during h.wake(), meaning that if the
thread is not sleeping, and action() causes it to exit, _detached_state
may also be destructed, and h.wake() will crash.

thread_handle is simply not needed for wake_with(), and was designed
with a completely different use case in mind (long-term holding of a
thread handler). We just need to use, in-line, the appropriate rcu
lock which keeps _detached_state alive. The resulting code is even
simpler, and nicely parallels the existing code of wake().

This patch fixes a real bug, but unfortunately we don't have a concrete
test-case which it is known to fix.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

include/sched.hh

@@ -650,9 +650,11 @@ template <class Action>
 inline
 void thread::wake_with(Action action)
 {
-    thread_handle h(handle());
-    action();
-    h.wake();
+    WITH_LOCK(osv::rcu_read_lock) {
+        auto ds = _detached_state.get();
+        action();
+        wake_impl(ds);
+    }
 }
 
 extern cpu __thread* current_cpu;