This information log message in flux-spindle.c hangs.

The problem is that the log message occurs before a call to setenv() (transferring the value of SPINDLE_TEST from the flux shell to the regular shell). The log message triggers initialization of the logging system, which checks for the SPINDLE_TEST environment variable, which isn't present, thus run_tests=0. After initialization completes and the message is logged, the remaining code in sp_init() executes, which includes setting SPINDLE_TEST=1. Subsequent processes see this different value and set up the test environment, but as the first process never did, the result is a hang.

In the two runs I looked at, only the smallest pid had run_test=0, which probably means flux calls sp_init() serially.

A simple solution is to move all of the setenv() code into flux_plugin_init() along with a note to not log anything until all calls to setenv() complete.