That probably comes from here:

~/src/golang.org/x$ grep -r TestSimpleCases
tools/imports/fix_test.go:func TestSimpleCases(t *testing.T) {

So, two questions:

1. Why is TestSimpleCases not cleaning up the directories in creates in /tmp? (@ianthehat, who owns golang.org/x/tools/imports at this point? Possibly @bradfitz or @heschik?)
2. Why is the builder using a “remove” operation that can fail to remove things? (If it is using rm -rf, it should probably chmod -R u+w before attempting that.)

When this happens, it goes into a loop of continually trying the remove and prevents the builder from running. This just started sometime in the past week.

I don't know why https://golang.org/cl/156078 wouldn't take care of this. I just double-checked and on my workstation it doesn't leave directories behind, even in cases of test failure. I guess we can change Cleanup() to return an error and maybe that'll shed light on the problem?

I can try a debug patch, if you have one. For now, I'm running the builder as root to work around this.

This is working now (running as not root), but I didn't really do anything other than rebuild the buildlet, which hadn't been refreshed in some time.