mm/gup: allow VM_FAULT_RETRY for multiple times

This is the gup counterpart of the change that allows the VM_FAULT_RETRY
to happen for more than once.  One thing to mention is that we must check
the fatal signal here before retry because the GUP can be interrupted by
that, otherwise we can loop forever.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Brian Geffon <bgeffon@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Link: http://lkml.kernel.org/r/20200220195357.16371-1-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index 4ae1a9b6a968acf634ec16df51fc3da3ff460197..efe9038933d969ba55e00b9c696e18c24d79fd21 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -868,7 +868,10 @@ 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;
        }
 
@@ -1228,7 +1231,6 @@ retry:
                down_read(&mm->mmap_sem);
                if (!(fault_flags & FAULT_FLAG_TRIED)) {
                        *unlocked = true;
-                       fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
                        fault_flags |= FAULT_FLAG_TRIED;
                        goto retry;
                }
@@ -1312,17 +1314,30 @@ 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
-                * FAULT_FLAG_TRIED.
+                * with both FAULT_FLAG_ALLOW_RETRY and
+                * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
+                * by fatal signals, so we need to check it before we
+                * start trying again otherwise it can loop forever.
                 */
+
+               if (fatal_signal_pending(current))
+                       break;
+
                *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 4d15525e9e33f009f82b316ba5ffda9589c570a4..0b15dc29e529807c4ad2aa8148042eb035b739a5 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4349,8 +4349,10 @@ 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);