[SRU][N][PATCH 1/2] mm: memcg: add NULL check to obj_cgroup_put()

[Juerg Haefliger]

From: Yosry Ahmed <yosryahmed at google.com>

BugLink: https://bugs.launchpad.net/bugs/2121673

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.com
Signed-off-by: Yosry Ahmed <yosryahmed at google.com>
Acked-by: Johannes Weiner <hannes at cmpxchg.org>
Acked-by: Roman Gushchin <roman.gushchin at linux.dev>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Muchun Song <muchun.song at linux.dev>
Cc: Shakeel Butt <shakeel.butt at linux.dev>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
(backported from commit 91b71e78b8e478e1a9af36b15ff1d38810572866)
[juergh: Adjusted context in mm/zswap.c]
Signed-off-by: Juerg Haefliger <juerg.haefliger at canonical.com>
---
 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 20ff87f8e001..f6b69b6111fe 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -819,7 +819,8 @@ 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 6eb2be9692f9..033ca15082eb 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -761,8 +761,7 @@ 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) {
@@ -778,8 +777,7 @@ 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 65d80602f1a6..33dc2bad0619 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2373,8 +2373,7 @@ 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);
 }
 
 /*
@@ -3149,8 +3148,7 @@ 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;
 		}
@@ -3422,8 +3420,7 @@ 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)
@@ -3550,8 +3547,7 @@ 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);
@@ -5490,8 +5486,7 @@ 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);
@@ -6665,8 +6660,7 @@ 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 55623c1e9074..bd69841a8653 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1715,8 +1715,7 @@ bool zswap_store(struct folio *folio)
 freepage:
 	zswap_entry_cache_free(entry);
 reject:
-	if (objcg)
-		obj_cgroup_put(objcg);
+	obj_cgroup_put(objcg);
 	return false;
 
 shrink:
-- 
2.48.1