I ran test_subprocess.test_preexec() 2000 times: I'm unable to reproduce the issue on my OpenIndiana VM, nor on Linux. I used this command:
gdb -args ./python -m test -F -m test_preexec test_subprocess 

The command on the buildbot is:
./python  ./Tools/scripts/run_tests.py -j 1 -u all -W --timeout=3600 -j4

http://buildbot.python.org/all/builders/AMD64%20OpenIndiana%203.x/builds/8549/steps/test/logs/stdio

[302/390/1] test_subprocess
Assertion failed: (result != NULL && !PyErr_Occurred()) || (result == NULL && PyErr_Occurred()), file Objects/abstract.c, line 2091
Fatal Python error: Aborted

Current thread 0x0000000000000001 (most recent call first):
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/subprocess.py", line 1396 in _execute_child
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/subprocess.py", line 865 in __init__
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/test_subprocess.py", line 1303 in test_preexec
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/case.py", line 577 in run
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/case.py", line 625 in __call__
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/suite.py", line 125 in run
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/suite.py", line 87 in __call__
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/suite.py", line 125 in run
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/suite.py", line 87 in __call__
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/unittest/runner.py", line 168 in run
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/support/__init__.py", line 1750 in _run_suite
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/support/__init__.py", line 1784 in run_unittest
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/test_subprocess.py", line 2470 in test_main
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/regrtest.py", line 1280 in runtest_inner
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/regrtest.py", line 967 in runtest
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/regrtest.py", line 532 in main
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/regrtest.py", line 1564 in main_in_temp_cwd
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/test/regrtest.py", line 1589 in <module>
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/runpy.py", line 85 in _run_code
  File "/export/home/buildbot/64bits/3.x.cea-indiana-amd64/build/Lib/runpy.py", line 170 in _run_module_as_main