Move lwlock-release probe back where it belongs

The documentation specifically states that lwlock-release fires before
any released waiters have been awakened.  It worked that way until
ab5194e, where is seems to have been
misplaced accidentally.  Move it back where it belongs.

Author: Craig Ringer <craig.ringer@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/CAGRY4nwxKUS_RvXFW-ugrZBYxPFFM5kjwKT5O+0+Stuga5b4+Q@mail.gmail.com

Author: petere

src/backend/storage/lmgr/lwlock.c

@@ -1840,6 +1840,7 @@ LWLockRelease(LWLock *lock)
 	/* nobody else can have that kind of lock */
 	Assert(!(oldstate & LW_VAL_EXCLUSIVE));
 
+	TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));
 
 	/*
 	 * We're still waiting for backends to get scheduled, don't wake them up
@@ -1863,8 +1864,6 @@ LWLockRelease(LWLock *lock)
 		LWLockWakeup(lock);
 	}
 
-	TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));
-
 	/*
 	 * Now okay to allow cancel/die interrupts.
 	 */