base: Fix event manager shutdown race on non-Linux platformswip/setnumcapabilities

During shutdown it's possible that we will attempt to use a closed fd
to wakeup another capability's event manager. On the Linux eventfd path
we were careful to handle this. However on the non-Linux path we failed
to do so. Fix this.

1 files changed, 10 insertions, 3 deletions

diff --git a/libraries/base/GHC/Event/Control.hs b/libraries/base/GHC/Event/Control.hs
index d80e054182..83b64fbb47 100644
--- a/libraries/base/GHC/Event/Control.hs
+++ b/libraries/base/GHC/Event/Control.hs
@@ -50,7 +50,7 @@ import System.Posix.Types (Fd)
 import Foreign.C.Error (throwErrnoIfMinus1, eBADF)
 import Foreign.C.Types (CULLong(..))
 #else
-import Foreign.C.Error (eAGAIN, eWOULDBLOCK)
+import Foreign.C.Error (eAGAIN, eWOULDBLOCK, eBADF)
 #endif
 
 data ControlMessage = CMsgWakeup
@@ -211,8 +211,15 @@ sendWakeup c = do
     _ | n /= -1   -> return ()
       | otherwise -> do
                    errno <- getErrno
-                   when (errno /= eAGAIN && errno /= eWOULDBLOCK) $
-                     throwErrno "sendWakeup"
+                   isDead <- readIORef (controlIsDead c)
+                   case () of
+                     _   -- Someone else has beat us to waking it up
+                       | errno == eAGAIN          -> return ()
+                       | errno == eWOULDBLOCK     -> return ()
+                         -- we are shutting down
+                       | errno == eBADF && isDead -> return ()
+                         -- something bad happened
+                       | otherwise                -> throwErrno "sendWakeup"
 #endif
 
 sendDie :: Control -> IO ()