[GHC] #9516: unsafeUnmask unmasks even inside uninterruptibleMask

[GHC]

#9516: unsafeUnmask unmasks even inside uninterruptibleMask
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              Reporter:  edsko       |            Owner:  simonmar
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Runtime     |          Version:  7.8.2
  System                             |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonmar):

 good catch, and a nice bug report.  I think `unsafeUnmask` is fine, but
 the implementation of `allowInterrupt` is wrong, and we should replace it
 with your version.  Would you like to submit a patch?  (I'm on holiday
 right now, but no need to wait for me to approve it, Austin can approve
 and push.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9516#comment:1>
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