Messages in this thread Patch in this message | | | From | Ralph Campbell <> | Subject | [PATCH] mm: move call to compound_head() in release_pages() | Date | Thu, 17 Sep 2020 10:39:38 -0700 |
| |
The function is_huge_zero_page() doesn't call compound_head() to make sure the page pointer is a head page. The call to is_huge_zero_page() in release_pages() is made before compound_head() is called so the test would fail if release_pages() was called with a tail page of the huge_zero_page and put_page_testzero() would be called releasing the page. This is unlikely to be happening in normal use or we would be seeing all sorts of process data corruption when accessing a THP zero page.
Looking at other places where is_huge_zero_page() is called, all seem to only pass a head page so I think the right solution is to move the call to compound_head() in release_pages() to a point before calling is_huge_zero_page().
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> ---
I found this by code inspection while working on my patch ("mm: remove extra ZONE_DEVICE struct page refcount").
This applies cleanly on the latest linux-mm and is for Andrew Morton's tree.
mm/swap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/swap.c b/mm/swap.c index eca95afe7ad4..7e79829a2e73 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -889,6 +889,7 @@ void release_pages(struct page **pages, int nr) locked_pgdat = NULL; } + page = compound_head(page); if (is_huge_zero_page(page)) continue; @@ -910,7 +911,6 @@ void release_pages(struct page **pages, int nr) } } - page = compound_head(page); if (!put_page_testzero(page)) continue; -- 2.20.1
| |