Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: [PATCH] mm: Convert mem_cgroup_id::ref to refcount_t type
From:   Kirill Tkhai <ktkhai@virtuozzo.com>
To:     akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org,
        vdavydov.dev@gmail.com, akpm@linux-foundation.org,
        ktkhai@virtuozzo.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Date:   Tue, 09 Oct 2018 20:46:56 +0300
Message-ID: <153910718919.7006.13400779039257185427.stgit@localhost.localdomain>
User-Agent: StGit/0.18
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This will allow to use generic refcount_t interfaces
to check counters overflow instead of currently existing
VM_BUG_ON(). The only difference after the patch is
VM_BUG_ON() may cause BUG(), while refcount_t fires
with WARN(). But this seems not to be significant here,
since such the problems are usually caught by syzbot
with panic-on-warn enabled.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 include/linux/memcontrol.h |    2 +-
 mm/memcontrol.c            |   10 ++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 4399cc3f00e4..7ab2120155a4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -78,7 +78,7 @@ struct mem_cgroup_reclaim_cookie {
 
 struct mem_cgroup_id {
 	int id;
-	atomic_t ref;
+	refcount_t ref;
 };
 
 /*
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7bebe2ddec05..aa728d5b3d72 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4299,14 +4299,12 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
 
 static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
 {
-	VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0);
-	atomic_add(n, &memcg->id.ref);
+	refcount_add(n, &memcg->id.ref);
 }
 
 static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
 {
-	VM_BUG_ON(atomic_read(&memcg->id.ref) < n);
-	if (atomic_sub_and_test(n, &memcg->id.ref)) {
+	if (refcount_sub_and_test(n, &memcg->id.ref)) {
 		mem_cgroup_id_remove(memcg);
 
 		/* Memcg ID pins CSS */
@@ -4523,7 +4521,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	}
 
 	/* Online state pins memcg ID, memcg ID pins CSS */
-	atomic_set(&memcg->id.ref, 1);
+	refcount_set(&memcg->id.ref, 1);
 	css_get(css);
 	return 0;
 }
@@ -6357,7 +6355,7 @@ subsys_initcall(mem_cgroup_init);
 #ifdef CONFIG_MEMCG_SWAP
 static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
 {
-	while (!atomic_inc_not_zero(&memcg->id.ref)) {
+	while (!refcount_inc_not_zero(&memcg->id.ref)) {
 		/*
 		 * The root cgroup cannot be destroyed, so it's refcount must
 		 * always be >= 1.