mm/memory.c: allow different return codes for copy_nonpresent_pte()

Currently if copy_nonpresent_pte() returns a non-zero value it is assumed
to be a swap entry which requires further processing outside the loop in
copy_pte_range() after dropping locks.  This prevents other values being
returned to signal conditions such as failure which a subsequent change
requires.

Instead make copy_nonpresent_pte() return an error code if further
processing is required and read the value for the swap entry in the main
loop under the ptl.

Link: https://lkml.kernel.org/r/20210524132725.12697-7-apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/mm/memory.c b/mm/memory.c
index db679744e8813beb9dcb142bae7e44b3b1b8bb3b..03d01c96dd114a0ed1e8ffd6ba95766a66f8903f 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -718,7 +718,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 
        if (likely(!non_swap_entry(entry))) {
                if (swap_duplicate(entry) < 0)
-                       return entry.val;
+                       return -EAGAIN;
 
                /* make sure dst_mm is on swapoff's mmlist. */
                if (unlikely(list_empty(&dst_mm->mmlist))) {
@@ -974,11 +974,13 @@ again:
                        continue;
                }
                if (unlikely(!pte_present(*src_pte))) {
-                       entry.val = copy_nonpresent_pte(dst_mm, src_mm,
-                                                       dst_pte, src_pte,
-                                                       src_vma, addr, rss);
-                       if (entry.val)
+                       ret = copy_nonpresent_pte(dst_mm, src_mm,
+                                               dst_pte, src_pte,
+                                               src_vma, addr, rss);
+                       if (ret == -EAGAIN) {
+                               entry = pte_to_swp_entry(*src_pte);
                                break;
+                       }
                        progress += 8;
                        continue;
                }