[Devel] [PATCH vz8 07/42] mm/gup: fix __get_user_pages() on fault retry of hugetlb

[Andrey Ryabinin]

From: Peter Xu <peterx at 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 at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Tested-by: Brian Geffon <bgeffon at google.com>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: Bobby Powers <bobbypowers at gmail.com>
Cc: David Hildenbrand <david at redhat.com>
Cc: Denis Plotnikov <dplotnikov at virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert at redhat.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Jerome Glisse <jglisse at redhat.com>
Cc: Johannes Weiner <hannes at cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill at shutemov.name>
Cc: Martin Cracauer <cracauer at cons.org>
Cc: Marty McFadden <mcfadden8 at llnl.gov>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Maya Gokhale <gokhale2 at llnl.gov>
Cc: Mel Gorman <mgorman at suse.de>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul at openvz.org>
Link: http://lkml.kernel.org/r/20200220155353.8676-3-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

https://jira.sw.ru/browse/PSBM-102938
(cherry picked from commit ad415db817964e96df824e8bb1a861527f8012b6)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/gup.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index f609ac36aa9a..e06aa55b65b2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -699,6 +699,15 @@ 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);
+					goto out;
+				}
 				continue;
 			}
 		}
@@ -755,6 +764,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		start += page_increm * PAGE_SIZE;
 		nr_pages -= page_increm;
 	} while (nr_pages);
+out:
 	return i;
 }
 
-- 
2.25.3