[PATCH v5 02/16] mm/gup: Fix __get_user_pages() on fault retry of hugetlb

[Peter Xu]

When follow_hugetlb_page() returns with *locked==0, it means we've got
a VM_FAULT_RETRY within the fauling process and we've released the
mmap_sem.  When that happens, we should stop and bail out.

Signed-off-by: Peter Xu <pet...@redhat.com>
---
 mm/gup.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index eddbb95dcb8f..e60d32f1674d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -833,6 +833,16 @@ static long __get_user_pages(struct task_struct *tsk, 
struct mm_struct *mm,
                                i = follow_hugetlb_page(mm, vma, pages, vmas,
                                                &start, &nr_pages, i,
                                                gup_flags, locked);
+                               if (locked && *locked == 0) {
+                                       /*
+                                        * We've got a VM_FAULT_RETRY
+                                        * and we've lost mmap_sem.
+                                        * We must stop here.
+                                        */
+                                       BUG_ON(gup_flags & FOLL_NOWAIT);
+                                       BUG_ON(ret != 0);
+                                       goto out;
+                               }
                                continue;
                        }
                }
-- 
2.21.0