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authorMike Kravetz <mike.kravetz@oracle.com>2021-09-02 14:58:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-09-03 09:58:16 -0700
commite32d20c0c88b1cd0a44f882c4f0eb2f536363d1b (patch)
tree4e74506a8be69cacd9365030d0103007913127f7 /mm/hugetlb.c
parentb65a4edae11ecd209a0f7c39e856de24678612d9 (diff)
hugetlb: before freeing hugetlb page set dtor to appropriate value
When removing a hugetlb page from the pool the ref count is set to one (as the free page has no ref count) and compound page destructor is set to NULL_COMPOUND_DTOR. Since a subsequent call to free the hugetlb page will call __free_pages for non-gigantic pages and free_gigantic_page for gigantic pages the destructor is not used. However, consider the following race with code taking a speculative reference on the page: Thread 0 Thread 1 -------- -------- remove_hugetlb_page set_page_refcounted(page); set_compound_page_dtor(page, NULL_COMPOUND_DTOR); get_page_unless_zero(page) __update_and_free_page __free_pages(page, huge_page_order(h)); /* Note that __free_pages() will simply drop the reference to the page. */ put_page(page) __put_compound_page() destroy_compound_page NULL_COMPOUND_DTOR BUG: kernel NULL pointer dereference, address: 0000000000000000 To address this race, set the dtor to the normal compound page dtor for non-gigantic pages. The dtor for gigantic pages does not matter as gigantic pages are changed from a compound page to 'just a group of pages' before freeing. Hence, the destructor is not used. Link: https://lkml.kernel.org/r/20210809184832.18342-4-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Reviewed-by: Muchun Song <songmuchun@bytedance.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: David Hildenbrand <david@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev> Cc: Mina Almasry <almasrymina@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c22
1 files changed, 21 insertions, 1 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8f97321396cc..dd1c1e7d970b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1370,8 +1370,28 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
h->surplus_huge_pages_node[nid]--;
}
+ /*
+ * Very subtle
+ *
+ * For non-gigantic pages set the destructor to the normal compound
+ * page dtor. This is needed in case someone takes an additional
+ * temporary ref to the page, and freeing is delayed until they drop
+ * their reference.
+ *
+ * For gigantic pages set the destructor to the null dtor. This
+ * destructor will never be called. Before freeing the gigantic
+ * page destroy_compound_gigantic_page will turn the compound page
+ * into a simple group of pages. After this the destructor does not
+ * apply.
+ *
+ * This handles the case where more than one ref is held when and
+ * after update_and_free_page is called.
+ */
set_page_refcounted(page);
- set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
+ if (hstate_is_gigantic(h))
+ set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
+ else
+ set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
h->nr_huge_pages--;
h->nr_huge_pages_node[nid]--;