From a734bcc812146cfba530e1adaf609fce1357982e Mon Sep 17 00:00:00 2001 From: Hillf Danton Date: Tue, 10 Jan 2012 15:07:20 -0800 Subject: [PATCH] hugetlb: detect race upon page allocation failure during COW Currently we are not rechecking pte_same in hugetlb_cow after we take ptl lock again in the page allocation failure code path and simply retry again. This is not an issue at the moment because hugetlb fault path is protected by hugetlb_instantiation_mutex so we cannot race. The original page is locked and so we cannot race even with the page migration. Let's add the pte_same check anyway as we want to be consistent with the other check later in this function and be safe if we ever remove the mutex. [mhocko@suse.cz: reworded the changelog] Signed-off-by: Hillf Danton Signed-off-by: Michal Hocko Cc: Andrea Arcangeli Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7acd12503f73..2c551b28ba69 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2408,7 +2408,14 @@ retry_avoidcopy: BUG_ON(page_count(old_page) != 1); BUG_ON(huge_pte_none(pte)); spin_lock(&mm->page_table_lock); - goto retry_avoidcopy; + ptep = huge_pte_offset(mm, address & huge_page_mask(h)); + if (likely(pte_same(huge_ptep_get(ptep), pte))) + goto retry_avoidcopy; + /* + * race occurs while re-acquiring page_table_lock, and + * our job is done. + */ + return 0; } WARN_ON_ONCE(1); } -- 2.30.2