Re: [PATCH] mm: deferred_init_memmap improvements

From: Anshuman Khandual
Date: Fri Oct 06 2017 - 02:49:26 EST

On 10/04/2017 08:59 PM, Pavel Tatashin wrote:
> This patch fixes another existing issue on systems that have holes in
> zones i.e CONFIG_HOLES_IN_ZONE is defined.
> In for_each_mem_pfn_range() we have code like this:
> if (!pfn_valid_within(pfn)
> goto free_range;
> Note: 'page' is not set to NULL and is not incremented but 'pfn' advances.

page is initialized to NULL at the beginning of the function.
PFN advances but we dont proceed unless pfn_valid_within(pfn)
holds true which basically should have checked with arch call
back if the PFN is valid in presence of memory holes as well.
Is not this correct ?

> Thus means if deferred struct pages are enabled on systems with these kind
> of holes, linux would get memory corruptions. I have fixed this issue by
> defining a new macro that performs all the necessary operations when we
> free the current set of pages.

If we bail out in case PFN is not valid, then how corruption
can happen ?