[merged mm-stable] memcg-clear-flushing_cached_charge-on-cpu-offline.patch removed from -mm tree

[merged mm-stable] memcg-clear-flushing_cached_charge-on-cpu-offline.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: memcg: clear FLUSHING_CACHED_CHARGE on cpu offline
has been removed from the -mm tree.  Its filename was
     memcg-clear-flushing_cached_charge-on-cpu-offline.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Shakeel Butt <shakeel.butt@linux.dev>
Subject: memcg: clear FLUSHING_CACHED_CHARGE on cpu offline
Date: Fri, 28 Aug 2026 12:24:19 -0700

Sashiko [1] reported that memcg_hotplug_cpu_dead() drains the stocks of
the CPU which went away but leaves FLUSHING_CACHED_CHARGE alone.

The flag can be set at that point: drain_all_stock() may have claimed the
stock and queued the drain work shortly before the CPU went down. 
workqueue_offline_cpu() unbinds the per-cpu workers, so such a pending
work item is executed by an unbound worker on some other CPU, where
drain_local_memcg_stock() operates on this_cpu_ptr() and thus drains and
clears the flag of that other CPU instead.  Nothing clears the flag of the
dead CPU, so drain_all_stock() would skip its stock forever once the CPU
comes back online.

Clear the flag of both stocks after draining them.

Link: https://lore.kernel.org/20260828192419.3057939-1-shakeel.butt@linux.dev
Link: https://sashiko.dev/#/patchset/20260828135036.7d44361f%40fangorn [1]
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
---

 mm/memcontrol.c |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

--- a/mm/memcontrol.c~memcg-clear-flushing_cached_charge-on-cpu-offline
+++ a/mm/memcontrol.c
@@ -2373,9 +2373,21 @@ void drain_all_stock(struct mem_cgroup *
 
 static int memcg_hotplug_cpu_dead(unsigned int cpu)
 {
+	struct memcg_stock_pcp *memcg_st = &per_cpu(memcg_stock, cpu);
+	struct obj_stock_pcp *obj_st = &per_cpu(obj_stock, cpu);
+
 	/* no need for the local lock */
-	drain_obj_stock(&per_cpu(obj_stock, cpu));
-	drain_stock_fully(&per_cpu(memcg_stock, cpu));
+	drain_obj_stock(obj_st);
+	drain_stock_fully(memcg_st);
+
+	/*
+	 * A drain work queued before the CPU went away is executed by an
+	 * unbound worker on some other CPU and clears that CPU's flag, so
+	 * clear the flags here to make these stocks drainable again once
+	 * the CPU comes back online.
+	 */
+	clear_bit(FLUSHING_CACHED_CHARGE, &memcg_st->flags);
+	clear_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags);
 
 	return 0;
 }
_

Patches currently in -mm which might be from shakeel.butt@linux.dev are

memcg-move-per-node-objcg-to-the-read-mostly-fields.patch
memcg-split-mem_cgroup_private_id-into-two-fields.patch
memcg-group-the-write-hot-fields-of-struct-mem_cgroup.patch
memcg-group-the-cold-fields-of-struct-mem_cgroup.patch
memcg-group-the-read-mostly-fields-of-struct-mem_cgroup.patch
memcg-group-the-fields-of-struct-mem_cgroup_per_node.patch