pkt_sched: remove unnecessary xchg() in packet classifiers

The use of xchg() hasn't been necessary since 2.2.something when proper
locking was added to packet schedulers. In the case of classifiers they
mostly weren't even necessary before that since they're mainly used
to assign a NULL pointer to the filter root in the ->destroy path;
the root is destroyed immediately after that.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_api.c

@@ -531,7 +531,8 @@ void tcf_exts_change(struct tcf_proto *tp, struct tcf_exts *dst,
 	if (src->action) {
 		struct tc_action *act;
 		tcf_tree_lock(tp);
-		act = xchg(&dst->action, src->action);
+		act = dst->action;
+		dst->action = src->action;
 		tcf_tree_unlock(tp);
 		if (act)
 			tcf_action_destroy(act, TCA_ACT_UNBIND);

net/sched/cls_basic.c

@@ -102,7 +102,7 @@ static inline void basic_delete_filter(struct tcf_proto *tp,
 
 static void basic_destroy(struct tcf_proto *tp)
 {
-	struct basic_head *head = (struct basic_head *) xchg(&tp->root, NULL);
+	struct basic_head *head = tp->root;
 	struct basic_filter *f, *n;
 
 	list_for_each_entry_safe(f, n, &head->flist, link) {

net/sched/cls_cgroup.c

@@ -201,9 +201,7 @@ static int cls_cgroup_change(struct tcf_proto *tp, unsigned long base,
 
 static void cls_cgroup_destroy(struct tcf_proto *tp)
 {
-	struct cls_cgroup_head *head;
-
-	head = (struct cls_cgroup_head *)xchg(&tp->root, NULL);
+	struct cls_cgroup_head *head = tp->root;
 
 	if (head) {
 		tcf_exts_destroy(tp, &head->exts);

net/sched/cls_fw.c

@@ -148,7 +148,7 @@ fw_delete_filter(struct tcf_proto *tp, struct fw_filter *f)
 
 static void fw_destroy(struct tcf_proto *tp)
 {
-	struct fw_head *head = (struct fw_head*)xchg(&tp->root, NULL);
+	struct fw_head *head = tp->root;
 	struct fw_filter *f;
 	int h;
 

net/sched/cls_route.c

@@ -260,7 +260,7 @@ route4_delete_filter(struct tcf_proto *tp, struct route4_filter *f)
 
 static void route4_destroy(struct tcf_proto *tp)
 {
-	struct route4_head *head = xchg(&tp->root, NULL);
+	struct route4_head *head = tp->root;
 	int h1, h2;
 
 	if (head == NULL)

net/sched/cls_tcindex.c

@@ -13,12 +13,6 @@
 #include <net/netlink.h>
 #include <net/pkt_cls.h>
 
-
-/*
- * Not quite sure if we need all the xchgs Alexey uses when accessing things.
- * Can always add them later ... :)
- */
-
 /*
  * Passing parameters to the root seems to be done more awkwardly than really
  * necessary. At least, u32 doesn't seem to use such dirty hacks. To be

net/sched/cls_u32.c

@@ -387,7 +387,7 @@ static int u32_destroy_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht)
 static void u32_destroy(struct tcf_proto *tp)
 {
 	struct tc_u_common *tp_c = tp->data;
-	struct tc_u_hnode *root_ht = xchg(&tp->root, NULL);
+	struct tc_u_hnode *root_ht = tp->root;
 
 	WARN_ON(root_ht == NULL);
 
@@ -479,7 +479,7 @@ static int u32_set_parms(struct tcf_proto *tp, unsigned long base,
 	err = -EINVAL;
 	if (tb[TCA_U32_LINK]) {
 		u32 handle = nla_get_u32(tb[TCA_U32_LINK]);
-		struct tc_u_hnode *ht_down = NULL;
+		struct tc_u_hnode *ht_down = NULL, *ht_old;
 
 		if (TC_U32_KEY(handle))
 			goto errout;
@@ -493,11 +493,12 @@ static int u32_set_parms(struct tcf_proto *tp, unsigned long base,
 		}
 
 		tcf_tree_lock(tp);
-		ht_down = xchg(&n->ht_down, ht_down);
+		ht_old = n->ht_down;
+		n->ht_down = ht_down;
 		tcf_tree_unlock(tp);
 
-		if (ht_down)
-			ht_down->refcnt--;
+		if (ht_old)
+			ht_old->refcnt--;
 	}
 	if (tb[TCA_U32_CLASSID]) {
 		n->res.classid = nla_get_u32(tb[TCA_U32_CLASSID]);