not being familiar with this case -- but from an outside perspective reading the mailing list now, seems Alan introduced a patch that broke userland code -- which is the biggest No-No in kernel hacking, ie. the number 1 rule is don't break userland. Alan appeared to argue userland code was broken and not his patch, which just made Linus mad (as expected). The kernel strives to never break userland, even when userland is relying on legacy and/or broken pieces of kernel code (the idea is to code around the broken parts and provide compatibility until userland changes/fixes their problem -- ie. no kernel change should ever mass-break userland code).