On Sat, 2005-02-26 at 19:09 -0800, David S. Miller wrote:
> .../...
> There are many pte level looping constructs of the form:
>
> pte = ...(pmd, address);
> address &= ~PMD_MASK;
> end = address + size;
> if (end > PMD_SIZE)
> end = PMD_SIZE;
>
> some_loop() {
> ...
> set_pte_at(mm, address, pte);
> address += PAGE_SIZE;
> pte++;
> ...
> }
>
> This "address" mask screws everything up.
>
> I know of at least three such cases so far, vmalloc.c:unmap_area_pte(),
> vmalloc.c:map_area_pte(), and mprotect.c:change_pte_range()
>
> The latter could definitely explain the behavior you are seeing on
> ppc64.
Indeed. Sorry, didn't have a chance to test myself yet here, but that's
definitely a bad one. Note that some of those functions use an address +
base (which would work, I suspect that was a later fix to the ones that
do pte_alloc etc...) and some use yet another scheme where the proper
address is passed along (the ones precalculating "next"). I prefer the
later version.
That's just another argument for having all these sharing common code,
even if it's a bit bulky macro at first, the current state of affairs is
just too prone to fail in weird ways.
Ben.
