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-rw-r--r--arch/s390/mm/gup.c24
1 files changed, 23 insertions, 1 deletions
diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index 45b405ca2567..668dda964f20 100644
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -48,11 +48,22 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
return 1;
}
+static inline void get_huge_page_tail(struct page *page)
+{
+ /*
+ * __split_huge_page_refcount() cannot run
+ * from under us.
+ */
+ VM_BUG_ON(page_mapcount(page) < 0);
+ VM_BUG_ON(atomic_read(&page->_count) != 0);
+ atomic_inc(&page->_mapcount);
+}
+
static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
unsigned long mask, result;
- struct page *head, *page;
+ struct page *head, *page, *tail;
int refs;
result = write ? 0 : _SEGMENT_ENTRY_RO;
@@ -64,6 +75,7 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
refs = 0;
head = pmd_page(pmd);
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+ tail = page;
do {
VM_BUG_ON(compound_head(page) != head);
pages[*nr] = page;
@@ -81,6 +93,16 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
*nr -= refs;
while (refs--)
put_page(head);
+ } else {
+ /*
+ * Any tail page need their mapcount reference taken
+ * before we return.
+ */
+ while (refs--) {
+ if (PageTail(tail))
+ get_huge_page_tail(tail);
+ tail++;
+ }
}
return 1;
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