[FIXED JENKINS-28690] Deadlock in hudson.model.Executor

- Rather fun one here. The Lock code relies on assuming that Thread.interrupted() is clear on entry
- If it then sees Thread.interrupted() set, it will interrupt the current thread in order to set the
  flag again.
- Executor is a thread that does funky things with an overridden interrupt method
- Executor.abortResult() is used to track a build be interrupted or aborted in some other way
- As a result the abortResult can cause a deadlockif there is a genuine interruption
- This fix clears the interrupt flag in abortResult() and uses the write lock in order to ensure:
    - The same lock as used in interrupt() is helf
    - The interrupt flag is clear
- Clearing the interrupt flag should be safe as the only time it is called is immediately after
  an interruption and the resulting exception is caught and rethrown/logged anyway

core/src/main/java/hudson/model/Executor.java

@@ -205,7 +205,14 @@ public class Executor extends Thread implements ModelObject {
     }
 
     public Result abortResult() {
-        lock.readLock().lock();
+        // this method is almost always called as a result of the current thread being interrupted
+        // as a result we need to clean the interrupt flag so that the lock's lock method doesn't
+        // get confused and think it was interrupted while awaiting the lock
+        Thread.interrupted(); 
+        // we need to use a write lock as we may be repeatedly interrupted while processing and
+        // we need the same lock as used in void interrupt(Result,boolean,CauseOfInterruption...)
+        // JENKINS-28690
+        lock.writeLock().lock();
         try {
             Result r = interruptStatus;
             if (r == null) r =
@@ -213,7 +220,7 @@ public class Executor extends Thread implements ModelObject {
 
             return r;
         } finally {
-            lock.readLock().unlock();
+            lock.writeLock().unlock();
         }
     }