s2k15: the stack overflow that wasn't

From the trenches ofs2k15:

There was a recent bug in OpenBSD install kernels. At random times during the install, messages like the following would appear:

/upgrade: //install.sub[168]: sleep: Cannot allocate memory/upgrade: //install.sub[168]: cat: Cannot allocate memory

This is pretty unusual. sleep and cat are not usually memory intensive. Clearly, something had changed. There were a fewinitial suspectsbut they had been pretty well tested. What was different?

Readthe whole thing to find out the answer!