Blocked STM transaction is not interruptible

import Control.Exception
import Control.Concurrent
import Control.Concurrent.STM
import Foreign.StablePtr

main :: IO ()
main = do
  tv <- atomically $ newTVar True
  _ <- newStablePtr tv
  t <- mask_ $ forkIO (blockSTM tv)
  killThread t

blockSTM :: TVar Bool -> IO ()
blockSTM tv = do
  atomically $ do
    v <- readTVar tv
    check $ not v

This code blocks forever. As I understand it, since the transaction blocks, it should be interruptible even despite the mask, and so killThread must succeed here, and the program should finish promptly.

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	simonmar
Operating system
Architecture