The patch titled
Subject: hugetlb: detect race upon page allocation failure during COW
has been added to the -mm tree. Its filename is
hugetlb-detect-race-upon-page-allocation-failure-during-cow.patch
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------------------------------------------------------
From: Hillf Danton <dhillf@xxxxxxxxx>
Subject: 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@xxxxxxx: reworded the changelog]
Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Johannes Weiner <jweiner@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff -puN mm/hugetlb.c~hugetlb-detect-race-upon-page-allocation-failure-during-cow mm/hugetlb.c
--- a/mm/hugetlb.c~hugetlb-detect-race-upon-page-allocation-failure-during-cow
+++ a/mm/hugetlb.c
@@ -2407,7 +2407,14 @@ 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);
}
_
Subject: Subject: hugetlb: detect race upon page allocation failure during COW
Patches currently in -mm which might be from dhillf@xxxxxxxxx are
origin.patch
linux-next.patch
hugetlb-detect-race-upon-page-allocation-failure-during-cow.patch
hugetlb-clarify-hugetlb_instantiation_mutex-usage.patch
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