+ memcg-drain-obj-stock-on-cpu-hotplug-teardown.patch added to mm-hotfixes-unstable branch

+ memcg-drain-obj-stock-on-cpu-hotplug-teardown.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: memcg: drain obj stock on cpu hotplug teardown
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     memcg-drain-obj-stock-on-cpu-hotplug-teardown.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-drain-obj-stock-on-cpu-hotplug-teardown.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Shakeel Butt <shakeel.butt@linux.dev>
Subject: memcg: drain obj stock on cpu hotplug teardown
Date: Mon, 10 Mar 2025 16:09:34 -0700

Currently on cpu hotplug teardown, only memcg stock is drained but we
need to drain the obj stock as well otherwise we will miss the stats
accumulated on the target cpu as well as the nr_bytes cached. The stats
include MEMCG_KMEM, NR_SLAB_RECLAIMABLE_B & NR_SLAB_UNRECLAIMABLE_B. In
addition we are leaking reference to struct obj_cgroup object.

Link: https://lkml.kernel.org/r/20250310230934.2913113-1-shakeel.butt@linux.dev
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc:
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/mm/memcontrol.c~memcg-drain-obj-stock-on-cpu-hotplug-teardown
+++ a/mm/memcontrol.c
@@ -1921,9 +1921,18 @@ void drain_all_stock(struct mem_cgroup *
 static int memcg_hotplug_cpu_dead(unsigned int cpu)
 {
 	struct memcg_stock_pcp *stock;
+	struct obj_cgroup *old;
+	unsigned long flags;
 
 	stock = &per_cpu(memcg_stock, cpu);
+
+	/* drain_obj_stock requires stock_lock */
+	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	old = drain_obj_stock(stock);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+
 	drain_stock(stock);
+	obj_cgroup_put(old);
 
 	return 0;
 }
_

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

memcg-drain-obj-stock-on-cpu-hotplug-teardown.patch
memcg-add-hierarchical-effective-limits-for-v2.patch
memcg-dont-call-propagate_protected_usage-for-v1.patch
page_counter-track-failcnt-only-for-legacy-cgroups.patch
page_counter-reduce-struct-page_counter-size.patch
memcg-bypass-root-memcg-check-for-skmem-charging.patch