linux-kernel - [PATCH v6 02/16] mm/gup: Fix __get_user

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Message-Id: <20200220145432.4561-3-peterx@redhat.com>
Date:   Thu, 20 Feb 2020 09:54:18 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Martin Cracauer <cracauer@...s.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>, peterx@...hat.com,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Marty McFadden <mcfadden8@...l.gov>,
        David Hildenbrand <david@...hat.com>,
        Bobby Powers <bobbypowers@...il.com>,
        Mel Gorman <mgorman@...e.de>
Subject: [PATCH v6 02/16] mm/gup: Fix __get_user_pages() on fault retry of hugetlb

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@...hat.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