datapath: Reduce locking requirements.

Reduce and clarify locking requirements for ovs_flow_cmd_alloc_info(),
ovs_flow_cmd_fill_info() and ovs_flow_cmd_build_info().

A datapath pointer is available only when holding a lock.  Change
ovs_flow_cmd_fill_info() and ovs_flow_cmd_build_info() to take a
dp_ifindex directly, rather than a datapath pointer that is then
(only) used to get the dp_ifindex.  This is useful, since the
dp_ifindex is available even when the datapath pointer is not, both
before and after taking a lock, which makes further critical section
reduction possible.

Make ovs_flow_cmd_alloc_info() take an 'acts' argument instead a
'flow' pointer.  This allows some future patches to do the allocation
before acquiring the flow pointer.

The locking requirements after this patch are:

ovs_flow_cmd_alloc_info(): May be called without locking, must not be
  called while holding the RCU read lock (due to memory allocation).
  If 'acts' belong to a flow in the flow table, however, then the
  caller must hold ovs_mutex.

ovs_flow_cmd_fill_info(): Either ovs_mutex or RCU read lock must be held.

ovs_flow_cmd_build_info(): This calls both of the above, so the caller
  must hold ovs_mutex.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

diff --git a/datapath/datapath.c b/datapath/datapath.c
index 0c77045..6f818f4 100644 (file)
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -664,7 +664,7 @@ static size_t ovs_flow_cmd_msg_size(const struct sw_flow_actions *acts)
 }
 
 /* Called with ovs_mutex or RCU read lock. */
-static int ovs_flow_cmd_fill_info(struct sw_flow *flow, struct datapath *dp,
+static int ovs_flow_cmd_fill_info(const struct sw_flow *flow, int dp_ifindex,
                                  struct sk_buff *skb, u32 portid,
                                  u32 seq, u32 flags, u8 cmd)
 {
@@ -681,7 +681,7 @@ static int ovs_flow_cmd_fill_info(struct sw_flow *flow, struct datapath *dp,
        if (!ovs_header)
                return -EMSGSIZE;
 
-       ovs_header->dp_ifindex = get_dpifindex(dp);
+       ovs_header->dp_ifindex = dp_ifindex;
 
        /* Fill flow key. */
        nla = nla_nest_start(skb, OVS_FLOW_ATTR_KEY);
@@ -704,6 +704,7 @@ static int ovs_flow_cmd_fill_info(struct sw_flow *flow, struct datapath *dp,
        nla_nest_end(skb, nla);
 
        ovs_flow_stats_get(flow, &stats, &used, &tcp_flags);
+
        if (used &&
            nla_put_u64(skb, OVS_FLOW_ATTR_USED, ovs_flow_used_time(used)))
                goto nla_put_failure;
@@ -731,9 +732,9 @@ static int ovs_flow_cmd_fill_info(struct sw_flow *flow, struct datapath *dp,
                const struct sw_flow_actions *sf_acts;
 
                sf_acts = rcu_dereference_ovsl(flow->sf_acts);
-
                err = ovs_nla_put_actions(sf_acts->actions,
                                          sf_acts->actions_len, skb);
+
                if (!err)
                        nla_nest_end(skb, start);
                else {
@@ -754,20 +755,17 @@ error:
        return err;
 }
 
-/* Must be called with ovs_mutex. */
-static struct sk_buff *ovs_flow_cmd_alloc_info(struct sw_flow *flow,
+/* May not be called with RCU read lock. */
+static struct sk_buff *ovs_flow_cmd_alloc_info(const struct sw_flow_actions *acts,
                                               struct genl_info *info,
                                               bool always)
 {
        struct sk_buff *skb;
-       size_t len;
 
        if (!always && !ovs_must_notify(info, &ovs_dp_flow_multicast_group))
                return NULL;
 
-       len = ovs_flow_cmd_msg_size(ovsl_dereference(flow->sf_acts));
-
-       skb = genlmsg_new_unicast(len, info, GFP_KERNEL);
+       skb = genlmsg_new_unicast(ovs_flow_cmd_msg_size(acts), info, GFP_KERNEL);
 
        if (!skb)
                return ERR_PTR(-ENOMEM);
@@ -775,21 +773,23 @@ static struct sk_buff *ovs_flow_cmd_alloc_info(struct sw_flow *flow,
        return skb;
 }
 
-/* Must be called with ovs_mutex. */
-static struct sk_buff *ovs_flow_cmd_build_info(struct sw_flow *flow,
-                                              struct datapath *dp,
-                                              struct genl_info *info,
-                                              u8 cmd, bool always)
+/* Called with ovs_mutex. */
+static struct sk_buff *ovs_flow_cmd_build_info(const struct sw_flow *flow,
+                                              int dp_ifindex,
+                                              struct genl_info *info, u8 cmd,
+                                              bool always)
 {
        struct sk_buff *skb;
        int retval;
 
-       skb = ovs_flow_cmd_alloc_info(flow, info, always);
+       skb = ovs_flow_cmd_alloc_info(ovsl_dereference(flow->sf_acts), info,
+                                     always);
        if (!skb || IS_ERR(skb))
                return skb;
 
-       retval = ovs_flow_cmd_fill_info(flow, dp, skb, info->snd_portid,
-                                       info->snd_seq, 0, cmd);
+       retval = ovs_flow_cmd_fill_info(flow, dp_ifindex, skb,
+                                       info->snd_portid, info->snd_seq, 0,
+                                       cmd);
        BUG_ON(retval < 0);
        return skb;
 }
@@ -870,8 +870,8 @@ static int ovs_flow_cmd_new_or_set(struct sk_buff *skb, struct genl_info *info)
                        goto err_flow_free;
                }
 
-               reply = ovs_flow_cmd_build_info(flow, dp, info,
-                                               OVS_FLOW_CMD_NEW, false);
+               reply = ovs_flow_cmd_build_info(flow, ovs_header->dp_ifindex,
+                                               info, OVS_FLOW_CMD_NEW, false);
        } else {
                /* We found a matching flow. */
                /* Bail out if we're not allowed to modify an existing flow.
@@ -897,8 +897,9 @@ static int ovs_flow_cmd_new_or_set(struct sk_buff *skb, struct genl_info *info)
                        rcu_assign_pointer(flow->sf_acts, acts);
                        ovs_nla_free_flow_actions(old_acts);
                }
-               reply = ovs_flow_cmd_build_info(flow, dp, info,
-                                               OVS_FLOW_CMD_NEW, false);
+
+               reply = ovs_flow_cmd_build_info(flow, ovs_header->dp_ifindex,
+                                               info, OVS_FLOW_CMD_NEW, false);
 
                /* Clear stats. */
                if (a[OVS_FLOW_ATTR_CLEAR])
@@ -960,7 +961,8 @@ static int ovs_flow_cmd_get(struct sk_buff *skb, struct genl_info *info)
                goto unlock;
        }
 
-       reply = ovs_flow_cmd_build_info(flow, dp, info, OVS_FLOW_CMD_NEW, true);
+       reply = ovs_flow_cmd_build_info(flow, ovs_header->dp_ifindex, info,
+                                       OVS_FLOW_CMD_NEW, true);
        if (IS_ERR(reply)) {
                err = PTR_ERR(reply);
                goto unlock;
@@ -1007,7 +1009,8 @@ static int ovs_flow_cmd_del(struct sk_buff *skb, struct genl_info *info)
                goto unlock;
        }
 
-       reply = ovs_flow_cmd_alloc_info(flow, info, false);
+       reply = ovs_flow_cmd_alloc_info(ovsl_dereference(flow->sf_acts), info,
+                                       false);
        if (IS_ERR(reply)) {
                err = PTR_ERR(reply);
                goto unlock;
@@ -1016,7 +1019,8 @@ static int ovs_flow_cmd_del(struct sk_buff *skb, struct genl_info *info)
        ovs_flow_tbl_remove(&dp->table, flow);
 
        if (reply) {
-               err = ovs_flow_cmd_fill_info(flow, dp, reply, info->snd_portid,
+               err = ovs_flow_cmd_fill_info(flow, ovs_header->dp_ifindex,
+                                            reply, info->snd_portid,
                                             info->snd_seq, 0,
                                             OVS_FLOW_CMD_DEL);
                BUG_ON(err < 0);
@@ -1057,7 +1061,7 @@ static int ovs_flow_cmd_dump(struct sk_buff *skb, struct netlink_callback *cb)
                if (!flow)
                        break;
 
-               if (ovs_flow_cmd_fill_info(flow, dp, skb,
+               if (ovs_flow_cmd_fill_info(flow, ovs_header->dp_ifindex, skb,
                                           NETLINK_CB(cb->skb).portid,
                                           cb->nlh->nlmsg_seq, NLM_F_MULTI,
                                           OVS_FLOW_CMD_NEW) < 0)