memcg: remove root memcg check from refill_stock

refill_stock can not be called with root memcg, so there is no need to
check it.  Instead add a warning if root is ever passed to it.

Link: https://lkml.kernel.org/r/20250404013913.1663035-1-shakeel.butt@linux.dev
Link: https://lkml.kernel.org/r/20250404013913.1663035-2-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b16b5b8..ae1e953 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1893,13 +1893,13 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
        unsigned long flags;
 
+       VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg));
+
        if (!local_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
                /*
                 * In case of unlikely failure to lock percpu stock_lock
                 * uncharge memcg directly.
                 */
-               if (mem_cgroup_is_root(memcg))
-                       return;
                page_counter_uncharge(&memcg->memory, nr_pages);
                if (do_memsw_account())
                        page_counter_uncharge(&memcg->memsw, nr_pages);