On Wed, Jan 19, 2022 at 04:27:32PM +0000, Matthew Wilcox wrote:
> On Wed, Jan 19, 2022 at 01:28:14PM +0000, Robin Murphy wrote:
> > > + if (WARN_ON(!pfn_valid(page_to_pfn(page))))
> >
> > Is it page_to_pfn() guaranteed to work without blowing up if page is invalid
> > in the first place? Looking at the CONFIG_SPARSEMEM case I'm not sure that's
> > true...
>
> Even if it does blow up, at least it's blowing up here where someone
> can start to debug it, rather than blowing up on first access, where
> we no longer have the invlid struct page pointer.
>
> I don't think we have a 'page_valid' function which will tell us whether
> a random pointer is actually a struct page or not.
Isn't it supposed to be:
if (!pfn_valid(pfn)) {
handle invalid pfn;
}
page = pfn_to_page(pfn);
Anything else - even trying to convert an invalid page back to a pfn,
could well be unreliable (sparsemem or discontigmem).
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