fix a deadlock

When finishedLiveUpdate was run on a different key than expected, it
blocked forever waiting for an indication the database had been updated.

Since the journal is locked when finishedLiveUpdate runs, this could
also have caused other git-annex commands to hang.

Annex/RepoSize/LiveUpdate.hs

@@ -59,14 +59,13 @@ prepareLiveUpdate mu k sc = do
 	startv <- liftIO newEmptyMVar
 	readyv <- liftIO newEmptyMVar
 	donev <- liftIO newEmptyMVar
-	finishv <- liftIO newEmptyMVar
-	void $ liftIO $ forkIO $ waitstart startv readyv donev finishv h u
-	return (LiveUpdate needv startv readyv donev finishv)
+	void $ liftIO $ forkIO $ waitstart startv readyv donev h u
+	return (LiveUpdate needv startv readyv donev)
   where
 	{- Wait for checkLiveUpdate to request a start, or for the
 	 - LiveUpdate to get garbage collected in the case where
 	 - it is not needed. -}
-	waitstart startv readyv donev finishv h u =
+	waitstart startv readyv donev h u =
 		tryNonAsync (takeMVar startv) >>= \case
 			Right () -> do
 				pid <- getCurrentPid
@@ -77,21 +76,23 @@ prepareLiveUpdate mu k sc = do
 				 - need live updates. -}
 				Db.startingLiveSizeChange h u k sc cid
 				putMVar readyv ()
-				waitdone donev finishv h u cid
+				waitdone donev h u cid
 			Left _ -> noop
 	
 	{- Wait for finishedLiveUpdate to be called, or for the LiveUpdate
 	 - to get garbage collected in the case where the change didn't
 	 - actually happen. Updates the database. -}
 	waitdone donev finishv h u cid = tryNonAsync (takeMVar donev) >>= \case
-		Right (Just (u', k', sc'))
+		Right (Just (u', k', sc', finishv))
 			| u' == u && k' == k && sc' == sc -> do
 				Db.successfullyFinishedLiveSizeChange h u k sc cid
 				putMVar finishv ()
 			-- This can happen when eg, storing to a cluster
 			-- causes fanout and so this is called with
 			-- other UUIDs.
-			| otherwise -> waitdone donev finishv h u cid
+			| otherwise -> do
+				putMVar finishv ()
+				waitdone donev finishv h u cid
 		Right Nothing -> abandoned h u cid
 		Left _ -> abandoned h u cid
 	abandoned h u cid = Db.removeStaleLiveSizeChange h u k sc cid
@@ -122,7 +123,7 @@ checkLiveUpdate lu a = do
 finishedLiveUpdate :: LiveUpdate -> UUID -> Key -> SizeChange -> IO ()
 finishedLiveUpdate NoLiveUpdate _ _ _ = noop
 finishedLiveUpdate lu u k sc = do
-	tryNonAsync (putMVar (liveUpdateDone lu) (Just (u, k, sc))) >>= \case
-		Right () -> void $
-			tryNonAsync $ readMVar $ liveUpdateFinish lu
+	finishv <- newEmptyMVar
+	tryNonAsync (putMVar (liveUpdateDone lu) (Just (u, k, sc, finishv))) >>= \case
+		Right () -> void $ tryNonAsync $ takeMVar finishv
 		Left _ -> noop

Types/RepoSize.hs

@@ -39,8 +39,7 @@ data LiveUpdate
 		{ liveUpdateNeeded :: MVar ()
 		, liveUpdateStart :: MVar ()
 		, liveUpdateReady :: MVar ()
-		, liveUpdateDone :: MVar (Maybe (UUID, Key, SizeChange))
-		, liveUpdateFinish :: MVar ()
+		, liveUpdateDone :: MVar (Maybe (UUID, Key, SizeChange, MVar ()))
 		}
 	| NoLiveUpdate