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Subject[PATCH] mm: Convert mem_cgroup_id::ref to refcount_t type
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Date
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.
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