thp: bail out gup_fast on splitting pmd

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@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index 06f56fc..269aa53 100644 (file)
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -160,7 +160,18 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
                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))