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Garbage collector crashes in simple parallel sorting program

I have a very simple parallel program that crashes quite reproducibly. On x86-64 and x86-32, the symptoms are subtly different, but equally catastrophic.

x86-64:

$ ghc -threaded -O2 --make -o Sorting Sorting
[1 of 1] Compiling Main             ( Sorting.hs, Sorting.o )
Linking Sorting ...
$ ./Sorting  +RTS -N2 -RTS 100000
100000
Segmentation fault

x86-32:

$ ghc -O2 --make -threaded -o Sorting Sorting
[1 of 1] Compiling Main             ( Sorting.hs, Sorting.o )
Linking Sorting ...
$ ./Sorting +RTS -N2 -RTS 125000
125000
Sorting: internal error: evacuate: strange closure type 17805
    (GHC version 6.8.2 for i386_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Aborted

Here's a somewhat useless backtrace from gdb on x86-64:

#1  0x00007fb49eac2d83 in abort () at abort.c:88
#2  0x0000000000444c45 in rtsFatalInternalErrorFn ()
#3  0x0000000000444efc in barf ()
#4  0x0000000000464c9c in evacuate ()
#5  0x000000000044d213 in scavenge_stack ()
#6  0x000000000044e4ba in scavenge_one ()
#7  0x000000000044e8d6 in scavenge_mutable_list ()
#8  0x000000000044bc49 in GarbageCollect ()
#9  0x0000000000445d1f in scheduleDoGC ()
#10 0x0000000000446ff8 in schedule ()
#11 0x0000000000447339 in workerStart ()
#12 0x0000000000f6c29a in start_thread (arg=<value optimized out>)
    at pthread_create.c:297
#13 0x00007fb49eb732cd in clone () from /lib64/libc.so.6
Edited by Simon Marlow