Merge tag 'mm-hotfixes-stable-2023-09-05-11-51' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull misc fixes from Andrew Morton:
 "Seven hotfixes. Four are cc:stable and the remainder pertain to issues
  which were introduced in the current merge window"

* tag 'mm-hotfixes-stable-2023-09-05-11-51' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm:
  sparc64: add missing initialization of folio in tlb_batch_add()
  mm: memory-failure: use rcu lock instead of tasklist_lock when collect_procs()
  revert "memfd: improve userspace warnings for missing exec-related flags".
  rcu: dump vmalloc memory info safely
  mm/vmalloc: add a safer version of find_vm_area() for debug
  tools/mm: fix undefined reference to pthread_once
  memcontrol: ensure memcg acquired by id is properly set up

1 files changed, 17 insertions, 5 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b29b850cf399..a4d3282493b6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5326,7 +5326,6 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	INIT_LIST_HEAD(&memcg->deferred_split_queue.split_queue);
 	memcg->deferred_split_queue.split_queue_len = 0;
 #endif
-	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
 	lru_gen_init_memcg(memcg);
 	return memcg;
 fail:
@@ -5398,14 +5397,27 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	if (alloc_shrinker_info(memcg))
 		goto offline_kmem;
 
-	/* Online state pins memcg ID, memcg ID pins CSS */
-	refcount_set(&memcg->id.ref, 1);
-	css_get(css);
-
 	if (unlikely(mem_cgroup_is_root(memcg)))
 		queue_delayed_work(system_unbound_wq, &stats_flush_dwork,
 				   FLUSH_TIME);
 	lru_gen_online_memcg(memcg);
+
+	/* Online state pins memcg ID, memcg ID pins CSS */
+	refcount_set(&memcg->id.ref, 1);
+	css_get(css);
+
+	/*
+	 * Ensure mem_cgroup_from_id() works once we're fully online.
+	 *
+	 * We could do this earlier and require callers to filter with
+	 * css_tryget_online(). But right now there are no users that
+	 * need earlier access, and the workingset code relies on the
+	 * cgroup tree linkage (mem_cgroup_get_nr_swap_pages()). So
+	 * publish it here at the end of onlining. This matches the
+	 * regular ID destruction during offlining.
+	 */
+	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
+
 	return 0;
 offline_kmem:
 	memcg_offline_kmem(memcg);