From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Force gup_fast to take the slow path and block if the pmd is splitting, not
only if it's none.
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Mel Gorman <mel@xxxxxxxxx>
---
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -160,7 +160,18 @@ static int gup_pmd_range(pud_t pud, unsi
pmd_t pmd = *pmdp;
next = pmd_addr_end(addr, end);
- if (pmd_none(pmd))
+ /*
+ * The pmd_trans_splitting() check below explains why
+ * pmdp_splitting_flush has to flush the tlb, to stop
+ * this gup-fast code from running while we set the
+ * splitting bit in the pmd. Returning zero will take
+ * the slow path that will call wait_split_huge_page()
+ * if the pmd is still in splitting state. gup-fast
+ * can't because it has irq disabled and
+ * wait_split_huge_page() would never return as the
+ * tlb flush IPI wouldn't run.
+ */
+ if (pmd_none(pmd) || pmd_trans_splitting(pmd))
return 0;
if (unlikely(pmd_large(pmd))) {
if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
--
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