Segfault when running with +RTS -N2

This program:

import Control.Concurrent
import Control.Concurrent.MVar
import Control.Exception
import System.IO

main :: IO ()
main = do hSetBuffering stdout NoBuffering
          let loop = doit >> loop
          loop

doit :: IO ()
doit = do v <- newMVar '.'
          t <- forkIO (foo v)
          threadDelay 1000
          killThread t
          takeMVar v >>= putChar

foo :: MVar Char -> IO ()
foo v = do let loop = do withMVar v $ \x -> evaluate x
                         loop
           loop

segfaults for me on amd64/Linux when compiled with a validated HEAD and run with +RTS -N2:

$ ghc --make j -threaded
[1 of 1] Compiling Main             ( j.hs, j.o )
Linking j ...
$ ./j +RTS -N2
zsh: segmentation fault  ./j +RTS -N2
$ ./j +RTS -N2
......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................zsh: segmentation fault  ./j +RTS -N2
$ ./j +RTS -N2
...........................................zsh: segmentation fault  ./j +RTS -N2

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
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