David I got this error on Windows today. It's during the testuite run of 'sh validate' =====> T7969(normal) 3998 of 6647 [0, 25, 1] cd "/c/Users/simonpj/AppData/Local/Temp/ghctest-b2z6dfqg/test spaces/rename/should_compile/T7969.run" && $MAKE -s --no-print-directory T7969 =====> T9127(normal) 3999 of 6647 [0, 25, 1] cd "/c/Users/simonpj/AppData/Local/Temp/ghctest-b2z6dfqg/test spaces/rename/should_compile/T9127.run" && "/c/code/HEAD/bindisttest/install dir/bin/ghc.exe" -c T9127.hs -dcore-lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show-caret -Werror=compat -dno-debug-output =====> T4426(normal) 4000 of 6647 [0, 25, 1] cd "/c/Users/simonpj/AppData/Local/Temp/ghctest-b2z6dfqg/test spaces/rename/should_compile/T4426.run" && "/c/code/HEAD/bindisttest/install dir/bin/ghc.exe" -c T4426.hs -dcore-lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show-caret -Werror=compat -dno-debug-output cd "/c/Users/simonpj/AppData/Local/Temp/ghctest-b2z6dfqg/test spaces/rename/should_compile/T5592.run" && ./T5592 =====> T9778(normal) 4001 of 6647 [0, 25, 1] cd "/c/Users/simonpj/AppData/Local/Temp/ghctest-b2z6dfqg/test spaces/rename/should_compile/T9778.run" && "/c/code/HEAD/bindisttest/install dir/bin/ghc.exe" -c T9778.hs -dcore-lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show-caret -Werror=compat -dno-debug-output -fwarn-unticked-promoted-constructors =====> T10816(normal) 4002 of 6647 [0, 25, 1] cd "/c/Users/simonpj/AppData/Local/Temp/ghctest-b2z6dfqg/test spaces/rename/should_compile/T10816.run" && "/c/code/HEAD/bindisttest/install dir/bin/ghc.exe" -c T10816.hs -dcore-lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show-caret -Werror=compat -dno-debug-output Traceback (most recent call last): File "/usr/lib/python3.6/threading.py", line 426, in acquire self._cond.wait(timeout) File "/usr/lib/python3.6/threading.py", line 287, in wait raise RuntimeError("cannot wait on un-acquired lock") RuntimeError: cannot wait on un-acquired lock During handling of the above exception, another exception occurred: Traceback (most recent call last): File "../driver/runtests.py", line 336, in <module> oneTest(watcher) File "/c/code/HEAD/testsuite/driver/testlib.py", line 717, in <lambda> thisTest = lambda watcher: runTest(watcher, myTestOpts, name, func, args) File "/c/code/HEAD/testsuite/driver/testlib.py", line 678, in runTest pool_sema.acquire() File "/usr/lib/python3.6/threading.py", line 429, in acquire rc = True File "/usr/lib/python3.6/threading.py", line 243, in __exit__ return self._lock.__exit__(*args) RuntimeError: release unlocked lock make: *** [../mk/test.mk:344: test] Error 1 make: Leaving directory '/c/code/HEAD/testsuite/tests' make: Entering directory '/c/code/HEAD/testsuite/tests/stage1' Does this ring any bells. It means I can't validate at all. Thanks Simon