net_sched: remove tc class reference counting

For TC classes, their ->get() and ->put() are always paired, and the
reference counting is completely useless, because:

1) For class modification and dumping paths, we already hold RTNL lock,
   so all of these ->get(),->change(),->put() are atomic.

2) For filter bindiing/unbinding, we use other reference counter than
   this one, and they should have RTNL lock too.

3) For ->qlen_notify(), it is special because it is called on ->enqueue()
   path, but we already hold qdisc tree lock there, and we hold this
   tree lock when graft or delete the class too, so it should not be gone
   or changed until we release the tree lock.

Therefore, this patch removes ->get() and ->put(), but:

1) Adds a new ->find() to find the pointer to a class by classid, no
   refcnt.

2) Move the original class destroy upon the last refcnt into ->delete(),
   right after releasing tree lock. This is fine because the class is
   already removed from hash when holding the lock.

For those who also use ->put() as ->unbind(), just rename them to reflect
this change.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 37 deletions

diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 1bdb0106f342..3ec8bec109bb 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -129,7 +129,6 @@ struct cbq_class {
 	struct tcf_proto __rcu	*filter_list;
 	struct tcf_block	*block;
 
-	int			refcnt;
 	int			filters;
 
 	struct cbq_class	*defaults[TC_PRIO_MAX + 1];
@@ -1155,7 +1154,6 @@ static int cbq_init(struct Qdisc *sch, struct nlattr *opt)
 	if (err < 0)
 		goto put_rtab;
 
-	q->link.refcnt = 1;
 	q->link.sibling = &q->link;
 	q->link.common.classid = sch->handle;
 	q->link.qdisc = sch;
@@ -1388,16 +1386,11 @@ static void cbq_qlen_notify(struct Qdisc *sch, unsigned long arg)
 	cbq_deactivate_class(cl);
 }
 
-static unsigned long cbq_get(struct Qdisc *sch, u32 classid)
+static unsigned long cbq_find(struct Qdisc *sch, u32 classid)
 {
 	struct cbq_sched_data *q = qdisc_priv(sch);
-	struct cbq_class *cl = cbq_class_lookup(q, classid);
 
-	if (cl) {
-		cl->refcnt++;
-		return (unsigned long)cl;
-	}
-	return 0;
+	return (unsigned long)cbq_class_lookup(q, classid);
 }
 
 static void cbq_destroy_class(struct Qdisc *sch, struct cbq_class *cl)
@@ -1443,25 +1436,6 @@ static void cbq_destroy(struct Qdisc *sch)
 	qdisc_class_hash_destroy(&q->clhash);
 }
 
-static void cbq_put(struct Qdisc *sch, unsigned long arg)
-{
-	struct cbq_class *cl = (struct cbq_class *)arg;
-
-	if (--cl->refcnt == 0) {
-#ifdef CONFIG_NET_CLS_ACT
-		spinlock_t *root_lock = qdisc_root_sleeping_lock(sch);
-		struct cbq_sched_data *q = qdisc_priv(sch);
-
-		spin_lock_bh(root_lock);
-		if (q->rx_class == cl)
-			q->rx_class = NULL;
-		spin_unlock_bh(root_lock);
-#endif
-
-		cbq_destroy_class(sch, cl);
-	}
-}
-
 static int
 cbq_change_class(struct Qdisc *sch, u32 classid, u32 parentid, struct nlattr **tca,
 		 unsigned long *arg)
@@ -1608,7 +1582,6 @@ cbq_change_class(struct Qdisc *sch, u32 classid, u32 parentid, struct nlattr **t
 
 	cl->R_tab = rtab;
 	rtab = NULL;
-	cl->refcnt = 1;
 	cl->q = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops, classid);
 	if (!cl->q)
 		cl->q = &noop_qdisc;
@@ -1689,12 +1662,7 @@ static int cbq_delete(struct Qdisc *sch, unsigned long arg)
 	cbq_rmprio(q, cl);
 	sch_tree_unlock(sch);
 
-	BUG_ON(--cl->refcnt == 0);
-	/*
-	 * This shouldn't happen: we "hold" one cops->get() when called
-	 * from tc_ctl_tclass; the destroy method is done from cops->put().
-	 */
-
+	cbq_destroy_class(sch, cl);
 	return 0;
 }
 
@@ -1760,8 +1728,7 @@ static const struct Qdisc_class_ops cbq_class_ops = {
 	.graft		=	cbq_graft,
 	.leaf		=	cbq_leaf,
 	.qlen_notify	=	cbq_qlen_notify,
-	.get		=	cbq_get,
-	.put		=	cbq_put,
+	.find		=	cbq_find,
 	.change		=	cbq_change_class,
 	.delete		=	cbq_delete,
 	.walk		=	cbq_walk,