[PATCH 7/7] mm/gup: Allow VM_FAULT_RETRY for multiple times

[Peter Xu]

This is the gup counterpart of the change that allows the VM_FAULT_RETRY
to happen for more than once.

Reviewed-by: Jerome Glisse <jglisse@xxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 mm/gup.c     | 17 +++++++++++++----
 mm/hugetlb.c |  6 ++++--
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 58d282115d9b..ac8d5b73c212 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -647,7 +647,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 	if (*flags & FOLL_TRIED) {
-		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
+		/*
+		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
+		 * can co-exist
+		 */
 		fault_flags |= FAULT_FLAG_TRIED;
 	}
 
@@ -1062,17 +1065,23 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 		if (likely(pages))
 			pages += ret;
 		start += ret << PAGE_SHIFT;
+		lock_dropped = true;
 
+retry:
 		/*
 		 * Repeat on the address that fired VM_FAULT_RETRY
-		 * without FAULT_FLAG_ALLOW_RETRY but with
+		 * with both FAULT_FLAG_ALLOW_RETRY and
 		 * FAULT_FLAG_TRIED.
 		 */
 		*locked = 1;
-		lock_dropped = true;
 		down_read(&mm->mmap_sem);
 		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
-				       pages, NULL, NULL);
+				       pages, NULL, locked);
+		if (!*locked) {
+			/* Continue to retry until we succeeded */
+			BUG_ON(ret != 0);
+			goto retry;
+		}
 		if (ret != 1) {
 			BUG_ON(ret > 1);
 			if (!pages_done)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ba179c2fa8fb..d9c739f9a28e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4317,8 +4317,10 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
 					FAULT_FLAG_RETRY_NOWAIT;
 			if (flags & FOLL_TRIED) {
-				VM_WARN_ON_ONCE(fault_flags &
-						FAULT_FLAG_ALLOW_RETRY);
+				/*
+				 * Note: FAULT_FLAG_ALLOW_RETRY and
+				 * FAULT_FLAG_TRIED can co-exist
+				 */
 				fault_flags |= FAULT_FLAG_TRIED;
 			}
 			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);
-- 
2.21.0