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Subject[PATCH] hugetlb: detect race if fail to COW
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In the error path that we fail to allocate new huge page, before try again, we
have to check race since page_table_lock is re-acquired.

If racing, our job is done.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---
--- a/mm/hugetlb.c Fri Nov 18 21:38:30 2011
+++ b/mm/hugetlb.c Fri Nov 18 21:48:15 2011
@@ -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);
}

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