[PATCH] mm: memcg: add NULL check to obj_cgroup_put()

[Yosry Ahmed <yosryahmed@xxxxxxxxxx>]

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.

Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
 include/linux/memcontrol.h |  3 ++-
 kernel/bpf/memalloc.c      |  6 ++----
 mm/memcontrol.c            | 18 ++++++------------
 mm/zswap.c                 |  3 +--
 4 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 394fd0a887ae7..b6264796815d4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -818,7 +818,8 @@ static inline void obj_cgroup_get_many(struct obj_cgroup *objcg,
 
 static inline void obj_cgroup_put(struct obj_cgroup *objcg)
 {
-	percpu_ref_put(&objcg->refcnt);
+	if (objcg)
+		percpu_ref_put(&objcg->refcnt);
 }
 
 static inline bool mem_cgroup_tryget(struct mem_cgroup *memcg)
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 550f02e2cb132..a546aba46d5da 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -759,8 +759,7 @@ 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);
+		obj_cgroup_put(ma->objcg);
 		destroy_mem_alloc(ma, rcu_in_progress);
 	}
 	if (ma->caches) {
@@ -776,8 +775,7 @@ 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);
+		obj_cgroup_put(ma->objcg);
 		destroy_mem_alloc(ma, rcu_in_progress);
 	}
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 138bcfa182344..aab3f5473203a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2370,8 +2370,7 @@ 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);
+	obj_cgroup_put(old);
 }
 
 /*
@@ -3147,8 +3146,7 @@ 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);
+			obj_cgroup_put(old);
 
 			old = NULL;
 		}
@@ -3420,8 +3418,7 @@ 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);
+	obj_cgroup_put(old);
 }
 
 static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
@@ -3548,8 +3545,7 @@ 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);
+	obj_cgroup_put(old);
 
 	if (nr_pages)
 		obj_cgroup_uncharge_pages(objcg, nr_pages);
@@ -5470,8 +5466,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 {
 	int node;
 
-	if (memcg->orig_objcg)
-		obj_cgroup_put(memcg->orig_objcg);
+	obj_cgroup_put(memcg->orig_objcg);
 
 	for_each_node(node)
 		free_mem_cgroup_per_node_info(memcg, node);
@@ -6622,8 +6617,7 @@ 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);
+	obj_cgroup_put(objcg);
 
 	/*
 	 * Some kernel allocations can happen after this point,
diff --git a/mm/zswap.c b/mm/zswap.c
index e0ec91995f4e3..3c2f960a789ba 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1533,8 +1533,7 @@ bool zswap_store(struct folio *folio)
 freepage:
 	zswap_entry_cache_free(entry);
 reject:
-	if (objcg)
-		obj_cgroup_put(objcg);
+	obj_cgroup_put(objcg);
 check_old:
 	/*
 	 * If the zswap store fails or zswap is disabled, we must invalidate the
-- 
2.44.0.291.gc1ea87d7ee-goog