mm/migration: fix potential page refcounts leak in migrate_pages

In -ENOMEM case, there might be some subpages of fail-to-migrate THPs left
in thp_split_pages list.  We should move them back to migration list so
that they could be put back to the right list by the caller otherwise the
page refcnt will be leaked here.  Also adjust nr_failed and nr_thp_failed
accordingly to make vm events account more accurate.

Link: https://lkml.kernel.org/r/20220318111709.60311-10-linmiaohe@huawei.com
Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 161a21314210cf9e4c075392a4c9c75f15d11913..173ba05070497112be623a80de786ea7c82e185c 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1434,6 +1434,14 @@ retry:
                                }
 
                                nr_failed_pages += nr_subpages;
+                               /*
+                                * There might be some subpages of fail-to-migrate THPs
+                                * left in thp_split_pages list. Move them back to migration
+                                * list so that they could be put back to the right list by
+                                * the caller otherwise the page refcnt will be leaked.
+                                */
+                               list_splice_init(&thp_split_pages, from);
+                               nr_thp_failed += thp_retry;
                                goto out;
                        case -EAGAIN:
                                if (is_thp)