openvswitch: 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>

1 files changed, 29 insertions, 25 deletions

diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index f3bcdac80bda..949fc7fadaf0 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -663,7 +663,7 @@ 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)
 {
@@ -680,7 +680,7 @@ 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);
@@ -703,6 +703,7 @@ 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;
@@ -730,9 +731,9 @@ 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 {
@@ -753,41 +754,40 @@ 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);
 
         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;
 }
@@ -868,8 +868,8 @@ 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.
@@ -895,8 +895,9 @@ 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])
@@ -958,7 +959,8 @@ 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;
@@ -1005,7 +1007,8 @@ 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;
@@ -1014,7 +1017,8 @@ 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);
@@ -1054,7 +1058,7 @@ 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)