Yes, that generic code won't work because of the NULL
Alpha, ARM, V32, FRV, IA64, MIPS, MN10300, PARISC, PPC,
SH, V850, X86, and Xtensa are all likely to run into
problems because of this change.
The only platform that did the check as a test of r->parent
being NULL is Powerpc.
The rest either didn't check (like sparc64), or tested it by going:
if (!r->start && r->end)
So the amount of potential breakage from this change is enormous.