1 files changed, 41 insertions, 54 deletions
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 86c5f1c0bad9..8686e329b8f2 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -11,11 +11,14 @@
 struct ucounts init_ucounts = {
 	.ns    = &init_user_ns,
 	.uid   = GLOBAL_ROOT_UID,
-	.count = ATOMIC_INIT(1),
+	.count = RCUREF_INIT(1),
 };
 
 #define UCOUNTS_HASHTABLE_BITS 10
-static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
+#define UCOUNTS_HASHTABLE_ENTRIES (1 << UCOUNTS_HASHTABLE_BITS)
+static struct hlist_nulls_head ucounts_hashtable[UCOUNTS_HASHTABLE_ENTRIES] = {
+	[0 ... UCOUNTS_HASHTABLE_ENTRIES - 1] = HLIST_NULLS_HEAD_INIT(0)
+};
 static DEFINE_SPINLOCK(ucounts_lock);
 
 #define ucounts_hashfn(ns, uid)						\
@@ -24,7 +27,6 @@ static DEFINE_SPINLOCK(ucounts_lock);
 #define ucounts_hashentry(ns, uid)	\
 	(ucounts_hashtable + ucounts_hashfn(ns, uid))
 
-
 #ifdef CONFIG_SYSCTL
 static struct ctl_table_set *
 set_lookup(struct ctl_table_root *root)
@@ -127,88 +129,73 @@ void retire_userns_sysctls(struct user_namespace *ns)
 #endif
 }
 
-static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
+static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid,
+				    struct hlist_nulls_head *hashent)
 {
 	struct ucounts *ucounts;
+	struct hlist_nulls_node *pos;
 
-	hlist_for_each_entry(ucounts, hashent, node) {
-		if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
-			return ucounts;
+	guard(rcu)();
+	hlist_nulls_for_each_entry_rcu(ucounts, pos, hashent, node) {
+		if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) {
+			if (rcuref_get(&ucounts->count))
+				return ucounts;
+		}
 	}
 	return NULL;
 }
 
 static void hlist_add_ucounts(struct ucounts *ucounts)
 {
-	struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
+	struct hlist_nulls_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
+
 	spin_lock_irq(&ucounts_lock);
-	hlist_add_head(&ucounts->node, hashent);
+	hlist_nulls_add_head_rcu(&ucounts->node, hashent);
 	spin_unlock_irq(&ucounts_lock);
 }
 
-static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
+struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
-	/* Returns true on a successful get, false if the count wraps. */
-	return !atomic_add_negative(1, &ucounts->count);
-}
+	struct hlist_nulls_head *hashent = ucounts_hashentry(ns, uid);
+	struct ucounts *ucounts, *new;
 
-struct ucounts *get_ucounts(struct ucounts *ucounts)
-{
-	if (!get_ucounts_or_wrap(ucounts)) {
-		put_ucounts(ucounts);
-		ucounts = NULL;
-	}
-	return ucounts;
-}
+	ucounts = find_ucounts(ns, uid, hashent);
+	if (ucounts)
+		return ucounts;
 
-struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
-{
-	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
-	bool wrapped;
-	struct ucounts *ucounts, *new = NULL;
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return NULL;
+
+	new->ns = ns;
+	new->uid = uid;
+	rcuref_init(&new->count, 1);
 
 	spin_lock_irq(&ucounts_lock);
 	ucounts = find_ucounts(ns, uid, hashent);
-	if (!ucounts) {
+	if (ucounts) {
 		spin_unlock_irq(&ucounts_lock);
-
-		new = kzalloc(sizeof(*new), GFP_KERNEL);
-		if (!new)
-			return NULL;
-
-		new->ns = ns;
-		new->uid = uid;
-		atomic_set(&new->count, 1);
-
-		spin_lock_irq(&ucounts_lock);
-		ucounts = find_ucounts(ns, uid, hashent);
-		if (!ucounts) {
-			hlist_add_head(&new->node, hashent);
-			get_user_ns(new->ns);
-			spin_unlock_irq(&ucounts_lock);
-			return new;
-		}
+		kfree(new);
+		return ucounts;
 	}
 
-	wrapped = !get_ucounts_or_wrap(ucounts);
+	hlist_nulls_add_head_rcu(&new->node, hashent);
+	get_user_ns(new->ns);
 	spin_unlock_irq(&ucounts_lock);
-	kfree(new);
-	if (wrapped) {
-		put_ucounts(ucounts);
-		return NULL;
-	}
-	return ucounts;
+	return new;
 }
 
 void put_ucounts(struct ucounts *ucounts)
 {
 	unsigned long flags;
 
-	if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
-		hlist_del_init(&ucounts->node);
+	if (rcuref_put(&ucounts->count)) {
+		spin_lock_irqsave(&ucounts_lock, flags);
+		hlist_nulls_del_rcu(&ucounts->node);
 		spin_unlock_irqrestore(&ucounts_lock, flags);
+
 		put_user_ns(ucounts->ns);
-		kfree(ucounts);
+		kfree_rcu(ucounts, rcu);
 	}
 }