avoid deadlocks when working with shared repos

Summary:
Lock ordering is important. When working with shared repos, when we
aquire a shared wlock, we must also acquire the master repo's wlock to ensure
that any operations that might later grab the lock are properly ordered.

Reviewed By: quark-zju, simpkins

Differential Revision: D9613877

fbshipit-source-id: 2c3eeeea534cdf49f3bd7e94db441c3a1479a959

mercurial/localrepo.py

@@ -1831,7 +1831,16 @@ class localrepository(object):
             if self._currentlock(self._lockref) is not None:
                 self.ui.develwarn('"wlock" acquired after "lock"')
 
+        # if this is a shared repo and we must also lock the shared wlock
+        # or else we can deadlock due to lock ordering issues
+        srcwlock = None
+        srcrepo = self._getsrcrepo()
+        if srcrepo:
+            srcwlock = srcrepo.wlock()
+
         def unlock():
+            if srcwlock:
+                srcwlock.release()
             if self.dirstate.pendingparentchange():
                 self.dirstate.invalidate()
             else: