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>

7 files changed, 12 insertions, 18 deletions

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 16e7ac9774e5..173fcc4b050d 100644
--- a/net/sched/cls_api.c
+++ b/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);
diff --git a/net/sched/cls_basic.c b/net/sched/cls_basic.c
index 956915c217d6..4e2bda854119 100644
--- a/net/sched/cls_basic.c
+++ b/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) {
diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c
index 53ada2c0e41c..0d68b1975983 100644
--- a/net/sched/cls_cgroup.c
+++ b/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);
diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index b0f90e593af0..6d6e87585fb1 100644
--- a/net/sched/cls_fw.c
+++ b/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;
 
diff --git a/net/sched/cls_route.c b/net/sched/cls_route.c
index e3d8455eebc2..bdf1f4172eef 100644
--- a/net/sched/cls_route.c
+++ b/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)
diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 7a7bff5ded24..e806f2314b5e 100644
--- a/net/sched/cls_tcindex.c
+++ b/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
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 246f9065ce34..05d178008cbc 100644
--- a/net/sched/cls_u32.c
+++ b/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]);