Nondeterministic T3424 timeouts on CI
The T3424 test case occasionally times out on CI, forcing me to restart builds to get a green build status. Here is one example from a validate-x86_64-linux-deb9-unreg run:
Timeout happened...killed process "cd "rts/T3424.run" && "/builds/ghc/ghc/inplace/bin/ghc-stage2" -o T3424 T3424.hs -dcore-lint -dstg-lint -dcmm-lint -no-user-package-db -rtsopts -optc-fno-builtin -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show-caret -Werror=compat -dno-debug-output "...
Compile failed (exit code 99) errors were:
[1 of 1] Compiling Main ( T3424.hs, T3424.o )
*** unexpected failure for T3424(normal)
<elided>
Unexpected results from:
TEST="T3424"
SUMMARY for test run started at Thu Feb 21 05:18:04 2019 UTC
1:15:50 spent to go through
6839 total tests, which gave rise to
21103 test cases, of which
13986 were skipped
38 had missing libraries
6977 expected passes
101 expected failures
0 caused framework failures
0 caused framework warnings
0 unexpected passes
1 unexpected failures
0 unexpected stat failures
Unexpected failures:
rts/T3424.run T3424 [exit code non-0] (normal)