On 2025-02-25 11:44, David Hildenbrand wrote:
On 24.02.25 22:59, Luiz Capitulino wrote:
The page_ext_next() function assumes that page extension objects for a
page order allocation always reside in the same memory section, which
may not be true and could lead to crashes. Use the new page_ext
iteration API instead.
Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios")
Signed-off-by: Luiz Capitulino <luizcap@xxxxxxxxxx>
---
mm/page_owner.c | 61 +++++++++++++++++++++++--------------------------
1 file changed, 29 insertions(+), 32 deletions(-)
[...]
void __reset_page_owner(struct page *page, unsigned short order)
@@ -293,11 +297,11 @@ void __reset_page_owner(struct page *page, unsigned short order)
page_owner = get_page_owner(page_ext);
alloc_handle = page_owner->handle;
+ page_ext_put(page_ext);
handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
- __update_page_owner_free_handle(page_ext, handle, order, current->pid,
+ __update_page_owner_free_handle(page, handle, order, current->pid,
current->tgid, free_ts_nsec);
- page_ext_put(page_ext);
I assume moving that is fine ...
but I'll not that ...
- for (i = 0; i < (1 << new_page_owner->order); i++) {
+ rcu_read_lock();
+ for_each_page_ext(&old->page, 1 << new_page_owner->order, page_ext, iter) {
+ old_page_owner = get_page_owner(page_ext);
old_page_owner->handle = migrate_handle;
- old_ext = page_ext_next(old_ext);
- old_page_owner = get_page_owner(old_ext);
}
+ rcu_read_unlock();
page_ext_put(new_ext);
page_ext_put(old_ext);
... here you are not moving it?
In general, LGTM, only the remaining page_ext_put() are a bit confusing.
Which part you found confusing: the fact that I'm not moving them up or that
we still make use of them?
For this hunk, I decided to keep them where they are because 'new_page_owner',
which is a page extension from 'next_ext', is still used in the last loop. So
I decided to free them all at the end for simplicity.
The other part is, page_ext_get() and page_ext_put() are still valid functions
for getting specific page extensions outside of loops and the usage in
__folio_copy_owner() (and a few other cases) seems valid to me.
