tmpfs: fix shmem_getpage_gfp() VM_BUG_ON

[~andy/linux] / mm / shmem.c

diff --git a/mm/shmem.c b/mm/shmem.c
index 67afba5117f2ebe80ef54e487d068fdf99e986bb..dc12264f44f571ea6c88c8e2d5ad42ce1c7087bd 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1145,8 +1145,20 @@ repeat:
                if (!error) {
                        error = shmem_add_to_page_cache(page, mapping, index,
                                                gfp, swp_to_radix_entry(swap));
-                       /* We already confirmed swap, and make no allocation */
-                       VM_BUG_ON(error);
+                       /*
+                        * We already confirmed swap under page lock, and make
+                        * no memory allocation here, so usually no possibility
+                        * of error; but free_swap_and_cache() only trylocks a
+                        * page, so it is just possible that the entry has been
+                        * truncated or holepunched since swap was confirmed.
+                        * shmem_undo_range() will have done some of the
+                        * unaccounting, now delete_from_swap_cache() will do
+                        * the rest (including mem_cgroup_uncharge_swapcache).
+                        * Reset swap.val? No, leave it so "failed" goes back to
+                        * "repeat": reading a hole and writing should succeed.
+                        */
+                       if (error)
+                               delete_from_swap_cache(page);
                }
                if (error)
                        goto failed;