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authorHillf Danton <dhillf@gmail.com>2012-01-10 15:07:20 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-10 16:30:42 -0800
commita734bcc812146cfba530e1adaf609fce1357982e (patch)
tree021fb4187985de65744a3f8f831a5f07130f2e2e /mm/hugetlb.c
parent5f8aefd44e64ed2f6950a1dcc77309b7dd9979f4 (diff)
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 <dhillf@gmail.com> Signed-off-by: Michal Hocko <mhocko@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Johannes Weiner <jweiner@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7acd12503f7..2c551b28ba6 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);
}