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-rw-r--r--include/linux/huge_mm.h41
-rw-r--r--include/linux/mm.h14
2 files changed, 12 insertions, 43 deletions
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index db512014e061..b826239bdce0 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -157,46 +157,6 @@ static inline int hpage_nr_pages(struct page *page)
return HPAGE_PMD_NR;
return 1;
}
-/*
- * compound_trans_head() should be used instead of compound_head(),
- * whenever the "page" passed as parameter could be the tail of a
- * transparent hugepage that could be undergoing a
- * __split_huge_page_refcount(). The page structure layout often
- * changes across releases and it makes extensive use of unions. So if
- * the page structure layout will change in a way that
- * page->first_page gets clobbered by __split_huge_page_refcount, the
- * implementation making use of smp_rmb() will be required.
- *
- * Currently we define compound_trans_head as compound_head, because
- * page->private is in the same union with page->first_page, and
- * page->private isn't clobbered. However this also means we're
- * currently leaving dirt into the page->private field of anonymous
- * pages resulting from a THP split, instead of setting page->private
- * to zero like for every other page that has PG_private not set. But
- * anonymous pages don't use page->private so this is not a problem.
- */
-#if 0
-/* This will be needed if page->private will be clobbered in split_huge_page */
-static inline struct page *compound_trans_head(struct page *page)
-{
- if (PageTail(page)) {
- struct page *head;
- head = page->first_page;
- smp_rmb();
- /*
- * head may be a dangling pointer.
- * __split_huge_page_refcount clears PageTail before
- * overwriting first_page, so if PageTail is still
- * there it means the head pointer isn't dangling.
- */
- if (PageTail(page))
- return head;
- }
- return page;
-}
-#else
-#define compound_trans_head(page) compound_head(page)
-#endif
extern int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, pmd_t pmd, pmd_t *pmdp);
@@ -226,7 +186,6 @@ static inline int split_huge_page(struct page *page)
do { } while (0)
#define split_huge_page_pmd_mm(__mm, __address, __pmd) \
do { } while (0)
-#define compound_trans_head(page) compound_head(page)
static inline int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
{
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f28f46eade6a..03ab3e58f511 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -399,8 +399,18 @@ static inline void compound_unlock_irqrestore(struct page *page,
static inline struct page *compound_head(struct page *page)
{
- if (unlikely(PageTail(page)))
- return page->first_page;
+ if (unlikely(PageTail(page))) {
+ struct page *head = page->first_page;
+
+ /*
+ * page->first_page may be a dangling pointer to an old
+ * compound page, so recheck that it is still a tail
+ * page before returning.
+ */
+ smp_rmb();
+ if (likely(PageTail(page)))
+ return head;
+ }
return page;
}