On 12/16/22 2:56 PM, John Hubbard wrote:
On 12/16/22 14:27, Andrew Morton wrote:
On Tue, 13 Dec 2022 13:20:53 -0800 Sidhartha Kumar
<sidhartha.kumar@xxxxxxxxxx> wrote:
folio_set_compound_order() is moved to an mm-internal location so
external
folio users cannot misuse this function. Change the name of the function
to folio_set_order() and use WARN_ON_ONCE() rather than BUG_ON. Also,
handle the case if a non-large folio is passed and add clarifying
comments
to the function.
This differs from the version I previously merged:
---
a/mm/internal.h~mm-move-folio_set_compound_order-to-mm-internalh-update
+++ a/mm/internal.h
@@ -384,8 +384,10 @@ int split_free_page(struct page *free_pa
*/
static inline void folio_set_order(struct folio *folio, unsigned int
order)
{
- if (WARN_ON_ONCE(!folio_test_large(folio)))
+ if (!folio_test_large(folio)) {
+ WARN_ON_ONCE(order);
return;
+ }
I think that's out of date?
We eventually settled on the version that is (as of this a few minutes
ago) already in mm-unstable (commit fdea060a130d: "mm: move
folio_set_compound_order() to mm/internal.h"), which has it like this:
Hi Andrew, yes this version that is already in mm-unstable represents
the v2 of this patch which is what we agreed on. I think the patch
mm-move-folio_set_compound_order-to-mm-internalh-update with description
"alter the folio_set_order() warning" which was just added to
mm-unstable should be removed as our discussion lead us away from that
version.
if (WARN_ON_ONCE(!folio_test_large(folio)))
return;
folio->_folio_order = order;
#ifdef CONFIG_64BIT
Makes sense. But wouldn't
if (WARN_ON_ONCE(order && !folio_test_large(folio)))
be clearer?
That's a little narrower of a check. But maybe that's desirable. Could
Ya I think it would helpful to have a wider catch for the warn as any
user calling folio_set_order() with a non-large folio should be aware as
they could misuse the folio later on even if they passed in a 0 order
because order itself would be an OOB access.
Thanks,
Sidhartha Kumar
someone (Mike, Muchun, Sidhartha) comment on which behavior is
preferable, please? I think I'm a little dizzy at this point. :)
thanks,
