[GHC] #8402: throwTo segfaults under -prof -threaded -with-rtsopts=N2

[GHC]

#8402: throwTo segfaults under -prof -threaded -with-rtsopts=N2
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        Reporter:  akio           |            Owner:
            Type:  bug            |           Status:  patch
        Priority:  highest        |        Milestone:  7.8.1
       Component:  Profiling      |          Version:  7.7
      Resolution:                 |         Keywords:
Operating System:  Linux          |     Architecture:  x86_64 (amd64)
 Type of failure:  Runtime crash  |       Difficulty:  Unknown
       Test Case:                 |       Blocked By:
        Blocking:                 |  Related Tickets:
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Comment (by ezyang):

 If that's the case, then checkGeneration in rts/sm/Sanity.c should be
 adjusted, because it means that we can do a full heap check on all GCs
 when `-N1`. I don't know if LDV is supposed to work with the threaded
 runtime.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8402#comment:8>
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