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* [PATCH RESEND v6 02/16] mm/gup: Fix __get_user_pages() on fault retry of hugetlb
From: Peter Xu @ 2020-02-20 15:53 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: Andrea Arcangeli, Martin Cracauer, Linus Torvalds, Mike Rapoport,
	Kirill A . Shutemov, Johannes Weiner, Dr . David Alan Gilbert,
	David Hildenbrand, Bobby Powers, Maya Gokhale, Jerome Glisse,
	Mike Kravetz, Matthew Wilcox, Marty McFadden, Mel Gorman, peterx,
	Hugh Dickins, Brian Geffon, Denis Plotnikov, Pavel Emelyanov
In-Reply-To: <20200220155353.8676-1-peterx@redhat.com>

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 <peterx@redhat.com>
---
 mm/gup.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 1b4411bd0042..76cb420c0fb7 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -849,6 +849,16 @@ 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;
 			}
 		}
-- 
2.24.1



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