From: Andrea Arcangeli Date: Wed, 2 Nov 2011 20:37:08 +0000 (-0700) Subject: powerpc: get_hugepte() don't put_page() the wrong page X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=405e44f2e312dd5dd63e5a9f459bffcbcd4368ef;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git powerpc: get_hugepte() don't put_page() the wrong page "page" may have changed to point to the next hugepage after the loop completed, The references have been taken on the head page, so the put_page must happen there too. This is a longstanding issue pre-thp inclusion. It's totally unclear how these page_cache_add_speculative and pte_val(pte) != pte_val(*ptep) checks are necessary across all the powerpc gup_fast code, when x86 doesn't need any of that: there's no way the page can be freed with irq disabled so we're guaranteed the atomic_inc will happen on a page with page_count > 0 (so not needing the speculative check). The pte check is also meaningless on x86: no need to rollback on x86 if the pte changed, because the pte can still change a CPU tick after the check succeeded and it won't be rolled back in that case. The important thing is we got a reference on a valid page that was mapped there a CPU tick ago. So not knowing the soft tlb refill code of ppc64 in great detail I'm not removing the "speculative" page_count increase and the pte checks across all the code, but unless there's a strong reason for it they should be later cleaned up too. If a pte can change from huge to non-huge (like it could happen with THP) passing a pte_t *ptep to gup_hugepte() would also require to repeat the is_hugepd in gup_hugepte(), but that shouldn't happen with hugetlbfs only so I'm not altering that. Signed-off-by: Andrea Arcangeli Cc: Peter Zijlstra Cc: Hugh Dickins Cc: Johannes Weiner Cc: Rik van Riel Cc: Mel Gorman Cc: KOSAKI Motohiro Cc: Benjamin Herrenschmidt Acked-by: David Gibson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c index 0b9a5c1901b..b649c288af9 100644 --- a/arch/powerpc/mm/hugetlbpage.c +++ b/arch/powerpc/mm/hugetlbpage.c @@ -429,7 +429,7 @@ static noinline int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long add if (unlikely(pte_val(pte) != pte_val(*ptep))) { /* Could be optimized better */ while (*nr) { - put_page(page); + put_page(head); (*nr)--; } }