From a9b576f7253e22528584f5aeb46edf0b6b007992 Mon Sep 17 00:00:00 2001 From: Ralph Campbell Date: Tue, 13 Oct 2020 16:56:00 -0700 Subject: [PATCH] mm: move call to compound_head() in release_pages() 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 Signed-off-by: Andrew Morton Reviewed-by: Andrew Morton Cc: Yu Zhao Cc: Dan Williams Cc: Matthew Wilcox Cc: Christoph Hellwig Link: https://lkml.kernel.org/r/20200917173938.16420-1-rcampbell@nvidia.com Signed-off-by: Linus Torvalds --- mm/swap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/swap.c b/mm/swap.c index f41ccd8eae94a..47a47681c86b7 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;