From 55bda43bb26d2c11eeedac742eff87a8ac34c106 Mon Sep 17 00:00:00 2001 From: Naoya Horiguchi Date: Thu, 14 Jul 2016 12:07:35 -0700 Subject: [PATCH] mm: rmap: call page_check_address() with sync enabled to avoid racy check The previous patch addresses the race between split_huge_pmd_address() and someone changing the pmd. The fix is only for splitting of normal thp (i.e. pmd-mapped thp,) and for splitting of pte-mapped thp there still is the similar race. For splitting pte-mapped thp, the pte's conversion is done by try_to_unmap_one(TTU_MIGRATION). This function checks page_check_address() to get the target pte, but it can return NULL under some race, leading to VM_BUG_ON() in freeze_page(). Fortunately, page_check_address() already has an argument to decide whether we do a quick/racy check or not, so let's flip it when called from freeze_page(). Link: http://lkml.kernel.org/r/1466990929-7452-2-git-send-email-n-horiguchi@ah.jp.nec.com Signed-off-by: Naoya Horiguchi Cc: Kirill A. Shutemov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/rmap.c b/mm/rmap.c index 0ea5d9071b32..e4b713a6ed7e 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1427,7 +1427,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, goto out; } - pte = page_check_address(page, mm, address, &ptl, 0); + pte = page_check_address(page, mm, address, &ptl, + PageTransCompound(page)); if (!pte) goto out; -- 2.20.1