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, 5 insertions, 25 deletions

diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 1d2f6235dfcf..2d0e8d4bdc29 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -20,7 +20,6 @@
 
 struct drr_class {
 	struct Qdisc_class_common	common;
-	unsigned int			refcnt;
 	unsigned int			filter_cnt;
 
 	struct gnet_stats_basic_packed		bstats;
@@ -111,7 +110,6 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
 	if (cl == NULL)
 		return -ENOBUFS;
 
-	cl->refcnt	   = 1;
 	cl->common.classid = classid;
 	cl->quantum	   = quantum;
 	cl->qdisc	   = qdisc_create_dflt(sch->dev_queue,
@@ -163,32 +161,15 @@ static int drr_delete_class(struct Qdisc *sch, unsigned long arg)
 	drr_purge_queue(cl);
 	qdisc_class_hash_remove(&q->clhash, &cl->common);
 
-	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().
-	 */
-
 	sch_tree_unlock(sch);
-	return 0;
-}
-
-static unsigned long drr_get_class(struct Qdisc *sch, u32 classid)
-{
-	struct drr_class *cl = drr_find_class(sch, classid);
 
-	if (cl != NULL)
-		cl->refcnt++;
-
-	return (unsigned long)cl;
+	drr_destroy_class(sch, cl);
+	return 0;
 }
 
-static void drr_put_class(struct Qdisc *sch, unsigned long arg)
+static unsigned long drr_search_class(struct Qdisc *sch, u32 classid)
 {
-	struct drr_class *cl = (struct drr_class *)arg;
-
-	if (--cl->refcnt == 0)
-		drr_destroy_class(sch, cl);
+	return (unsigned long)drr_find_class(sch, classid);
 }
 
 static struct tcf_block *drr_tcf_block(struct Qdisc *sch, unsigned long cl)
@@ -478,8 +459,7 @@ static void drr_destroy_qdisc(struct Qdisc *sch)
 static const struct Qdisc_class_ops drr_class_ops = {
 	.change		= drr_change_class,
 	.delete		= drr_delete_class,
-	.get		= drr_get_class,
-	.put		= drr_put_class,
+	.find		= drr_search_class,
 	.tcf_block	= drr_tcf_block,
 	.bind_tcf	= drr_bind_tcf,
 	.unbind_tcf	= drr_unbind_tcf,