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From:   Peter Xu <peterx@redhat.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     David Hildenbrand <david@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Maya Gokhale <gokhale2@llnl.gov>,
        Jerome Glisse <jglisse@redhat.com>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Johannes Weiner <hannes@cmpxchg.org>, peterx@redhat.com,
        Martin Cracauer <cracauer@cons.org>,
        Marty McFadden <mcfadden8@llnl.gov>, Shaohua Li <shli@fb.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Denis Plotnikov <dplotnikov@virtuozzo.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: [PATCH v4 02/10] mm/gup: Fix __get_user_pages() on fault retry of hugetlb
Date:   Mon, 23 Sep 2019 12:25:15 +0800
Message-Id: <20190923042523.10027-3-peterx@redhat.com>
In-Reply-To: <20190923042523.10027-1-peterx@redhat.com>
References: <20190923042523.10027-1-peterx@redhat.com>
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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 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