async swapin

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f0cd9db..8af703d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2404,8 +2404,9 @@ static void __collapse_huge_page_swapin(struct mm_struct *mm,
                        continue;
                swapped_in++;
                ret = do_swap_page(mm, vma, _address, pte, pmd,
-                                  FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT,
+                                  FAULT_FLAG_ALLOW_RETRY,
                                   pteval);
+               down_read(&mm->mmap_sem);
                if (ret & VM_FAULT_ERROR) {
                        trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
                        return;
@@ -2491,8 +2492,13 @@ static void collapse_huge_page(struct mm_struct *mm,
         * Don't perform swapin readahead when the system is under pressure,
         * to avoid unnecessary resource consumption.
         */
-       if (allocstall == curr_allocstall && swap != 0)
+       if (allocstall == curr_allocstall && swap != 0) {
+               up_write(&mm->mmap_sem);
+               down_read(&mm->mmap_sem);
                __collapse_huge_page_swapin(mm, vma, address, pmd);
+               up_read(&mm->mmap_sem);
+               down_write(&mm->mmap_sem);
+       }

        anon_vma_lock_write(vma->anon_vma);