Thanks for the suggestions. Yep, its really worn out all the way. Left with a wafer thin strip of braking rubber. I guess you could say its a x-mart bike, costs less than 150, but pretty solidly built. Much ligher than x-mart bikes, and much better components too (relative).

Front pads are also wearing out, though they still could probably last about 500km more or so.

Also, the rim braking surface is quite bad (when i just slide my finger across it, can feel the ridges quite distinctly. any way to smoothen it out)

Once again, thanks!