From: Ralph Campbell <rcampbell@xxxxxxxxxx> Subject: 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(). Link: https://lkml.kernel.org/r/20200917173938.16420-1-rcampbell@xxxxxxxxxx Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Yu Zhao <yuzhao@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/swap.c~mm-move-call-to-compound_head-in-release_pages +++ a/mm/swap.c @@ -889,6 +889,7 @@ void release_pages(struct page **pages, locked_pgdat = NULL; } + page = compound_head(page); if (is_huge_zero_page(page)) continue; @@ -910,7 +911,6 @@ void release_pages(struct page **pages, } } - page = compound_head(page); if (!put_page_testzero(page)) continue; _
