Hollow processes

(Had the same problem on 2.5.9 with poldek, now it appeared on 2.5.15dj1 while building glibc-2.5.4 to rpm)
Process is hanging. It's impossible to stop it (even SAK is just clearing console). It's impossible to check what the process is (trying to read /proc/{pid}/{anyting} causes reading process to hang in the same way (so we have now 2 hanging processes). Trying to use ps/lsof/killall/{anything that is using /proc/{pid} causes this software hang in the same way. What could it be?
WK