On 11/20/22 6:31 PM, John Hubbard wrote:
On 11/18/22 14:20, Sidhartha Kumar wrote:
...
@@ -1950,7 +1949,7 @@ pgoff_t hugetlb_basepage_index(struct page *page)
return (index << compound_order(page_head)) + compound_idx;
}
-static struct page *alloc_buddy_huge_page(struct hstate *h,
+static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
gfp_t gfp_mask, int nid, nodemask_t *nmask,
nodemask_t *node_alloc_noretry)
{
@@ -2009,7 +2008,7 @@ static struct page
*alloc_buddy_huge_page(struct hstate *h,
if (node_alloc_noretry && !page && alloc_try_hard)
node_set(nid, *node_alloc_noretry);
- return page;
+ return page_folio(page);
1. This causes a NULL pointer crash when the user requests too many
hugetlb
pages (you can probably guess how I know this, haha), for example:
echo 50000 > /proc/sys/vm/nr_hugepages
...because page_folio() doesn't have a NULL check in there. You will want
to do something like this, on top of this current patch:
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 629bb044f063..ffb0f052bbff 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1987,11 +1987,6 @@ static struct folio
*alloc_buddy_hugetlb_folio(struct hstate *h,
page = NULL;
}
- if (page)
- __count_vm_event(HTLB_BUDDY_PGALLOC);
- else
- __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
-
/*
* If we did not specify __GFP_RETRY_MAYFAIL, but still got a
page this
* indicates an overall state change. Clear bit so that we
resume
@@ -2008,6 +2003,12 @@ static struct folio
*alloc_buddy_hugetlb_folio(struct hstate *h,
if (node_alloc_noretry && !page && alloc_try_hard)
node_set(nid, *node_alloc_noretry);
+ if (!page) {
+ __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
+ return NULL;
+ }
+
+ __count_vm_event(HTLB_BUDDY_PGALLOC);
return page_folio(page);
}
2. And also, the tests should probably be augmented to run this simple
(but easy to overlook) test.
Sure, I can look into adding this type of test to Linux Test Project.
3. And finally, the basic method of replacing page with page_folio(page)
is not sufficient, as you can see here. So I'd suggest taking a look
through your series to see if you are checking for NULL first, before
calling page_folio(page).
I will go through my series again to check for possible NULL dereferences.
Thanks for taking a look.
Sidhartha Kumar
thanks,
