On Sun, Jan 08, 2012 at 11:19:14AM +0100, Peter Zijlstra wrote:

> But even then, we limit PROP_MAX_SHIFT to 3*BITS_PER_LONG/4, I don't
> think that could ever overflow.

do_div() only uses the lower 32 bit value of the 64 bit denominator,
which may happen to be 0.

The denominator is not really 64 bit, but limited by PROP_MAX_SHIFT =
48 bit, however that upper limit looks not enough.

Ilya, would you help try the attached patch instead?

Thanks,
Fengguang