After I upgraded to 7.10.1 I started noticing that my shakefile would lock up on exit. It's after the 'main' function exits, and none of the shake tests have a problem, so presumably it's a GHC thing, that shake somehow causes to happen. Only kill -9 gets it to quit. Here's a stack trace from the OS X sampler: Call graph: 2801 Thread_909901 DispatchQueue_2: com.apple.libdispatch-manager (serial) 2801 _dispatch_mgr_thread (in libdispatch.dylib) + 52 [0x7fff8828ca6a] 2801 kevent64 (in libsystem_kernel.dylib) + 10 [0x7fff90ec0232] Total number in stack (recursive counted multiple, when >=5): Sort by top of stack, same collapsed (when >= 5): kevent64 (in libsystem_kernel.dylib) 2801 I know there aren't a lot of details here, but does this sound familiar to anyone? I can't see anything on https://ghc.haskell.org/trac/ghc/wiki/Status/GHC-7.10.2 that looks like this. Is there any way I can get more information I can get to report this? It used to be frequent (once in 10 runs maybe), but later became quite infrequent (once in a couple hundred runs, maybe). I downgraded to 7.8.4 and it hasn't happened again.