From 770a5370226cb207461bbad902543381c1fad521 Mon Sep 17 00:00:00 2001 From: Gerald Schaefer Date: Wed, 8 Jun 2016 15:33:50 -0700 Subject: [PATCH] mm: thp: broken page count after commit aa88b68c3b1d Christian Borntraeger reported a kernel panic after corrupt page counts, and it turned out to be a regression introduced with commit aa88b68c3b1d ("thp: keep huge zero page pinned until tlb flush"), at least on s390. put_huge_zero_page() was moved over from zap_huge_pmd() to release_pages(), and it was replaced by tlb_remove_page(). However, release_pages() might not always be triggered by (the arch-specific) tlb_remove_page(). On s390 we call free_page_and_swap_cache() from tlb_remove_page(), and not tlb_flush_mmu() -> free_pages_and_swap_cache() like the generic version, because we don't use the MMU-gather logic. Although both functions have very similar names, they are doing very unsimilar things, in particular free_page_xxx is just doing a put_page(), while free_pages_xxx calls release_pages(). This of course results in very harmful put_page()s on the huge zero page, on architectures where tlb_remove_page() is implemented in this way. It seems to affect only s390 and sh, but sh doesn't have THP support, so the problem (currently) probably only exists on s390. The following quick hack fixed the issue: Link: http://lkml.kernel.org/r/20160602172141.75c006a9@thinkpad Signed-off-by: Gerald Schaefer Reported-by: Christian Borntraeger Tested-by: Christian Borntraeger Cc: "Kirill A. Shutemov" Cc: Andrea Arcangeli Cc: "Aneesh Kumar K.V" Cc: Mel Gorman Cc: Hugh Dickins Cc: Johannes Weiner Cc: Dave Hansen Cc: Vlastimil Babka Cc: Martin Schwidefsky Cc: Heiko Carstens Cc: [4.6.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_state.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index 0d457e7db8d6..c99463ac02fb 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -252,7 +252,10 @@ static inline void free_swap_cache(struct page *page) void free_page_and_swap_cache(struct page *page) { free_swap_cache(page); - put_page(page); + if (is_huge_zero_page(page)) + put_huge_zero_page(); + else + put_page(page); } /* -- 2.20.1