mm: filter out swapin error entry in shmem mapping

There might be swapin error entries in shmem mapping.  Filter them out to
avoid "Bad swap file entry" complaint.

Link: https://lkml.kernel.org/r/20220519125030.21486-6-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/madvise.c

@@ -248,10 +248,13 @@ static void force_shm_swapin_readahead(struct vm_area_struct *vma,
 
 		if (!xa_is_value(page))
 			continue;
+		swap = radix_to_swp_entry(page);
+		/* There might be swapin error entries in shmem mapping. */
+		if (non_swap_entry(swap))
+			continue;
 		xas_pause(&xas);
 		rcu_read_unlock();
 
-		swap = radix_to_swp_entry(page);
 		page = read_swap_cache_async(swap, GFP_HIGHUSER_MOVABLE,
 					     NULL, 0, false, &splug);
 		if (page)

mm/swap_state.c

@@ -410,6 +410,9 @@ struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
 		return NULL;
 
 	swp = radix_to_swp_entry(page);
+	/* There might be swapin error entries in shmem mapping. */
+	if (non_swap_entry(swp))
+		return NULL;
 	/* Prevent swapoff from happening to us */
 	si = get_swap_device(swp);
 	if (!si)