mm: memcg: add NULL check to obj_cgroup_put()

9 out of 16 callers perform a NULL check before calling obj_cgroup_put(). 
Move the NULL check in the function, similar to mem_cgroup_put().  The
unlikely() NULL check in current_objcg_update() was left alone to avoid
dropping the unlikey() annotation as this a fast path.

Link: https://lkml.kernel.org/r/20240316015803.2777252-1-yosryahmed@google.comSigned-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -818,6 +818,7 @@ static inline void obj_cgroup_get_many(struct obj_cgroup *objcg,
 
 static inline void obj_cgroup_put(struct obj_cgroup *objcg)
 {
+	if (objcg)
 		percpu_ref_put(&objcg->refcnt);
 }
 

kernel/bpf/memalloc.c

@@ -759,7 +759,6 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 			rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
 			rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
 		}
-		if (ma->objcg)
 		obj_cgroup_put(ma->objcg);
 		destroy_mem_alloc(ma, rcu_in_progress);
 	}
@@ -776,7 +775,6 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 				rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
 			}
 		}
-		if (ma->objcg)
 		obj_cgroup_put(ma->objcg);
 		destroy_mem_alloc(ma, rcu_in_progress);
 	}

mm/memcontrol.c

@@ -2369,7 +2369,6 @@ static void drain_local_stock(struct work_struct *dummy)
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 
 	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
-	if (old)
 	obj_cgroup_put(old);
 }
 
@@ -3145,7 +3144,6 @@ static struct obj_cgroup *current_objcg_update(void)
 		if (old) {
 			old = (struct obj_cgroup *)
 				((unsigned long)old & ~CURRENT_OBJCG_UPDATE_FLAG);
-			if (old)
 			obj_cgroup_put(old);
 
 			old = NULL;
@@ -3418,7 +3416,6 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 		mod_objcg_mlstate(objcg, pgdat, idx, nr);
 
 	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
-	if (old)
 	obj_cgroup_put(old);
 }
 
@@ -3546,7 +3543,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	}
 
 	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
-	if (old)
 	obj_cgroup_put(old);
 
 	if (nr_pages)
@@ -5468,7 +5464,6 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 {
 	int node;
 
-	if (memcg->orig_objcg)
 	obj_cgroup_put(memcg->orig_objcg);
 
 	for_each_node(node)
@@ -6620,7 +6615,6 @@ static void mem_cgroup_exit(struct task_struct *task)
 
 	objcg = (struct obj_cgroup *)
 		((unsigned long)objcg & ~CURRENT_OBJCG_UPDATE_FLAG);
-	if (objcg)
 	obj_cgroup_put(objcg);
 
 	/*

mm/zswap.c

@@ -1618,7 +1618,6 @@ bool zswap_store(struct folio *folio)
 freepage:
 	zswap_entry_cache_free(entry);
 reject:
-	if (objcg)
 	obj_cgroup_put(objcg);
 check_old:
 	/*