From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Subject: hugetlb: remove prep_compound_huge_page cleanup Patch series "Fix prep_compound_gigantic_page ref count adjustment". These patches address the possible race between prep_compound_gigantic_page and __page_cache_add_speculative as described by Jann Horn in [1]. The first patch simply removes the unnecessary/obsolete helper routine prep_compound_huge_page to make the actual fix a little simpler. The second patch is the actual fix and has a detailed explanation in the commit message. This potential issue has existed for almost 10 years and I am unaware of anyone actually hitting the race. I did not cc stable, but would be happy to squash the patches and send to stable if anyone thinks that is a good idea. [1] https://lore.kernel.org/linux-mm/CAG48ez23q0Jy9cuVnwAe7t_fdhMk2S7N5Hdi-GLcCeq5bsfLxw@xxxxxxxxxxxxxx/ This patch (of 2): I could not think of a reliable way to recreate the issue for testing. Rather, I 'simulated errors' to exercise all the error paths. The routine prep_compound_huge_page is a simple wrapper to call either prep_compound_gigantic_page or prep_compound_page. However, it is only called from gather_bootmem_prealloc which only processes gigantic pages. Eliminate the routine and call prep_compound_gigantic_page directly. Link: https://lkml.kernel.org/r/20210622021423.154662-1-mike.kravetz@xxxxxxxxxx Link: https://lkml.kernel.org/r/20210622021423.154662-2-mike.kravetz@xxxxxxxxxx Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Youquan Song <youquan.song@xxxxxxxxx> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 29 ++++++++++------------------- 1 file changed, 10 insertions(+), 19 deletions(-) --- a/mm/hugetlb.c~hugetlb-remove-prep_compound_huge_page-cleanup +++ a/mm/hugetlb.c @@ -1320,8 +1320,6 @@ static struct page *alloc_gigantic_page( return alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask); } -static void prep_new_huge_page(struct hstate *h, struct page *page, int nid); -static void prep_compound_gigantic_page(struct page *page, unsigned int order); #else /* !CONFIG_CONTIG_ALLOC */ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask, int nid, nodemask_t *nodemask) @@ -2759,16 +2757,10 @@ found: return 1; } -static void __init prep_compound_huge_page(struct page *page, - unsigned int order) -{ - if (unlikely(order > (MAX_ORDER - 1))) - prep_compound_gigantic_page(page, order); - else - prep_compound_page(page, order); -} - -/* Put bootmem huge pages into the standard lists after mem_map is up */ +/* + * Put bootmem huge pages into the standard lists after mem_map is up. + * Note: This only applies to gigantic (order > MAX_ORDER) pages. + */ static void __init gather_bootmem_prealloc(void) { struct huge_bootmem_page *m; @@ -2777,20 +2769,19 @@ static void __init gather_bootmem_preall struct page *page = virt_to_page(m); struct hstate *h = m->hstate; + VM_BUG_ON(!hstate_is_gigantic(h)); WARN_ON(page_count(page) != 1); - prep_compound_huge_page(page, huge_page_order(h)); + prep_compound_gigantic_page(page, huge_page_order(h)); WARN_ON(PageReserved(page)); prep_new_huge_page(h, page, page_to_nid(page)); put_page(page); /* free it into the hugepage allocator */ /* - * If we had gigantic hugepages allocated at boot time, we need - * to restore the 'stolen' pages to totalram_pages in order to - * fix confusing memory reports from free(1) and another - * side-effects, like CommitLimit going negative. + * We need to restore the 'stolen' pages to totalram_pages + * in order to fix confusing memory reports from free(1) and + * other side-effects, like CommitLimit going negative. */ - if (hstate_is_gigantic(h)) - adjust_managed_page_count(page, pages_per_huge_page(h)); + adjust_managed_page_count(page, pages_per_huge_page(h)); cond_resched(); } } _
