On Mon, Apr 19, 2021 at 02:56:17PM +0300, Mike Rapoport wrote:
> On Mon, Apr 19, 2021 at 12:23:02PM +0100, Matthew Wilcox wrote:
> > So you're calling page_is_secretmem() on a struct page without having
> > a refcount on it. That is definitely not allowed. secretmem seems to
> > be full of these kinds of races; I know this isn't the first one I've
> > seen in it. I don't think this patchset is ready for this merge window.
>
> There were races in the older version that did caching of large pages and
> those were fixed then, but this is anyway irrelevant because all that code
> was dropped in the latest respins.
>
> I don't think that the fix of the race in gup_pte_range is that significant
> to wait 3 more months because of it.
I have no particular interest in secretmem, but it seems that every time
I come across it while looking at something else, I see these kinds of
major mistakes in it. That says to me it's not ready and hasn't seen
enough review.
> > With that fixed, you'll have a head page that you can use for testing,
> > which means you don't need to test PageCompound() (because you know the
> > page isn't PageTail), you can just test PageHead().
>
> I can't say I follow you here. page_is_secretmem() is intended to be a
> generic test, so I don't see how it will get PageHead() if it is called
> from other places.
static inline bool head_is_secretmem(struct page *head)
{
if (PageHead(head))
return false;
...
}
static inline bool page_is_secretmem(struct page *page)
{
if (PageTail(page))
return false;
return head_is_secretmem(page);
}
(yes, calling it head is a misnomer, because it's not necessarily a head,
it might be a base page, but until we have a name for pages which might
be a head page or a base page, it'll have to do ...)
