memcg: drain obj stock on cpu hotplug teardown

commit 9f01b4954490d4ccdbcc2b9be34a9921ceee9cbb upstream.

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>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ae1d184d035a4dfb96fa9eaba48291975fd544ee..2d1e402f06f22a7a2e64eba4f9e8d66b6f193b2b 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1882,9 +1882,18 @@ void drain_all_stock(struct mem_cgroup *root_memcg)
 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;
 }