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/20210616105937.23201-7-apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Peter Xu <peterx@redhat.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: John Hubbard <jhubbard@nvidia.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index e30488e..75feddb 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -717,7 +717,7 @@ 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 -EIO;
 
                /* make sure dst_mm is on swapoff's mmlist. */
                if (unlikely(list_empty(&dst_mm->mmlist))) {
@@ -973,12 +973,14 @@ again:
                        continue;
                }
                if (unlikely(!pte_present(*src_pte))) {
-                       entry.val = copy_nonpresent_pte(dst_mm, src_mm,
-                                                       dst_pte, src_pte,
-                                                       dst_vma, src_vma,
-                                                       addr, rss);
-                       if (entry.val)
+                       ret = copy_nonpresent_pte(dst_mm, src_mm,
+                                                 dst_pte, src_pte,
+                                                 dst_vma, src_vma,
+                                                 addr, rss);
+                       if (ret == -EIO) {
+                               entry = pte_to_swp_entry(*src_pte);
                                break;
+                       }
                        progress += 8;
                        continue;
                }
@@ -1011,20 +1013,24 @@ again:
        pte_unmap_unlock(orig_dst_pte, dst_ptl);
        cond_resched();
 
-       if (entry.val) {
+       if (ret == -EIO) {
+               VM_WARN_ON_ONCE(!entry.val);
                if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) {
                        ret = -ENOMEM;
                        goto out;
                }
                entry.val = 0;
-       } else if (ret) {
-               WARN_ON_ONCE(ret != -EAGAIN);
+       } else if (ret ==  -EAGAIN) {
                prealloc = page_copy_prealloc(src_mm, src_vma, addr);
                if (!prealloc)
                        return -ENOMEM;
-               /* We've captured and resolved the error. Reset, try again. */
-               ret = 0;
+       } else if (ret) {
+               VM_WARN_ON_ONCE(1);
        }
+
+       /* We've captured and resolved the error. Reset, try again. */
+       ret = 0;
+
        if (addr != end)
                goto again;
 out: