bonding: initial RCU conversion

This patch does the initial bonding conversion to RCU. After it the
following modes are protected by RCU alone: roundrobin, active-backup,
broadcast and xor. Modes ALB/TLB and 3ad still acquire bond->lock for
reading, and will be dealt with later. curr_active_slave needs to be
dereferenced via rcu in the converted modes because the only thing
protecting the slave after this patch is rcu_read_lock, so we need the
proper barrier for weakly ordered archs and to make sure we don't have
stale pointer. It's not tagged with __rcu yet because there's still work
to be done to remove the curr_slave_lock, so sparse will complain when
rcu_assign_pointer and rcu_dereference are used, but the alternative to use
rcu_dereference_protected would've created much bigger code churn which is
more difficult to test and review. That will be converted in time.

1. Active-backup mode
 1.1 Perf recording while doing iperf -P 4
  - old bonding: iperf spent 0.55% in bonding, system spent 0.29% CPU
                 in bonding
  - new bonding: iperf spent 0.29% in bonding, system spent 0.15% CPU
                 in bonding
 1.2. Bandwidth measurements
  - old bonding: 16.1 gbps consistently
  - new bonding: 17.5 gbps consistently

2. Round-robin mode
 2.1 Perf recording while doing iperf -P 4
  - old bonding: iperf spent 0.51% in bonding, system spent 0.24% CPU
                 in bonding
  - new bonding: iperf spent 0.16% in bonding, system spent 0.11% CPU
                 in bonding
 2.2 Bandwidth measurements
  - old bonding: 8 gbps (variable due to packet reorderings)
  - new bonding: 10 gbps (variable due to packet reorderings)

Of course the latency has improved in all converted modes, and moreover
while
doing enslave/release (since it doesn't affect tx anymore).

Also I've stress tested all modes doing enslave/release in a loop while
transmitting traffic.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 32 insertions, 29 deletions

diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
index 7d46fa832c1f..90102652c82a 100644
--- a/drivers/net/bonding/bond_3ad.c
+++ b/drivers/net/bonding/bond_3ad.c
@@ -2426,6 +2426,7 @@ int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
         struct ad_info ad_info;
         int res = 1;
 
+        read_lock(&bond->lock);
         if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
                 pr_debug("%s: Error: __bond_3ad_get_active_agg_info failed\n",
                          dev->name);
@@ -2475,6 +2476,7 @@ int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
         }
 
 out:
+        read_unlock(&bond->lock);
         if (res) {
                 /* no suitable interface, frame not sent */
                 kfree_skb(skb);
diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
index 4d35196b4b5a..3a5db7b1df68 100644
--- a/drivers/net/bonding/bond_alb.c
+++ b/drivers/net/bonding/bond_alb.c
@@ -1337,6 +1337,7 @@ int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
 
         /* make sure that the curr_active_slave do not change during tx
          */
+        read_lock(&bond->lock);
         read_lock(&bond->curr_slave_lock);
 
         switch (ntohs(skb->protocol)) {
@@ -1441,11 +1442,12 @@ int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
         }
 
         read_unlock(&bond->curr_slave_lock);
-
+        read_unlock(&bond->lock);
         if (res) {
                 /* no suitable interface, frame not sent */
                 kfree_skb(skb);
         }
+
         return NETDEV_TX_OK;
 }
 
@@ -1663,7 +1665,7 @@ void bond_alb_handle_active_change(struct bonding *bond, struct slave *new_slave
         }
 
         swap_slave = bond->curr_active_slave;
-        bond->curr_active_slave = new_slave;
+        rcu_assign_pointer(bond->curr_active_slave, new_slave);
 
         if (!new_slave || list_empty(&bond->slave_list))
                 return;
diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 5eee95c3b172..1d37a9657e0d 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -77,6 +77,7 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <net/pkt_sched.h>
+#include <linux/rculist.h>
 #include "bonding.h"
 #include "bond_3ad.h"
 #include "bond_alb.h"
@@ -1037,7 +1038,7 @@ void bond_change_active_slave(struct bonding *bond, struct slave *new_active)
                 if (new_active)
                         bond_set_slave_active_flags(new_active);
         } else {
-                bond->curr_active_slave = new_active;
+                rcu_assign_pointer(bond->curr_active_slave, new_active);
         }
 
         if (bond->params.mode == BOND_MODE_ACTIVEBACKUP) {
@@ -1127,7 +1128,7 @@ void bond_select_active_slave(struct bonding *bond)
  */
 static void bond_attach_slave(struct bonding *bond, struct slave *new_slave)
 {
-        list_add_tail(&new_slave->list, &bond->slave_list);
+        list_add_tail_rcu(&new_slave->list, &bond->slave_list);
         bond->slave_cnt++;
 }
 
@@ -1143,7 +1144,7 @@ static void bond_attach_slave(struct bonding *bond, struct slave *new_slave)
  */
 static void bond_detach_slave(struct bonding *bond, struct slave *slave)
 {
-        list_del(&slave->list);
+        list_del_rcu(&slave->list);
         bond->slave_cnt--;
 }
 
@@ -1751,7 +1752,7 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
                  * so we can change it without calling change_active_interface()
                  */
                 if (!bond->curr_active_slave && new_slave->link == BOND_LINK_UP)
-                        bond->curr_active_slave = new_slave;
+                        rcu_assign_pointer(bond->curr_active_slave, new_slave);
 
                 break;
         } /* switch(bond_mode) */
@@ -1951,7 +1952,7 @@ static int __bond_release_one(struct net_device *bond_dev,
         }
 
         if (all) {
-                bond->curr_active_slave = NULL;
+                rcu_assign_pointer(bond->curr_active_slave, NULL);
         } else if (oldcurrent == slave) {
                 /*
                  * Note that we hold RTNL over this sequence, so there
@@ -1983,6 +1984,7 @@ static int __bond_release_one(struct net_device *bond_dev,
 
         write_unlock_bh(&bond->lock);
         unblock_netpoll_tx();
+        synchronize_rcu();
 
         if (list_empty(&bond->slave_list)) {
                 call_netdevice_notifiers(NETDEV_CHANGEADDR, bond->dev);
@@ -3811,7 +3813,7 @@ void bond_xmit_slave_id(struct bonding *bond, struct sk_buff *skb, int slave_id)
         int i = slave_id;
 
         /* Here we start from the slave with slave_id */
-        bond_for_each_slave(bond, slave) {
+        bond_for_each_slave_rcu(bond, slave) {
                 if (--i < 0) {
                         if (slave_can_tx(slave)) {
                                 bond_dev_queue_xmit(bond, skb, slave->dev);
@@ -3822,7 +3824,7 @@ void bond_xmit_slave_id(struct bonding *bond, struct sk_buff *skb, int slave_id)
 
         /* Here we start from the first slave up to slave_id */
         i = slave_id;
-        bond_for_each_slave(bond, slave) {
+        bond_for_each_slave_rcu(bond, slave) {
                 if (--i < 0)
                         break;
                 if (slave_can_tx(slave)) {
@@ -3848,7 +3850,7 @@ static int bond_xmit_roundrobin(struct sk_buff *skb, struct net_device *bond_dev
          * will send all of this type of traffic.
          */
         if (iph->protocol == IPPROTO_IGMP && skb->protocol == htons(ETH_P_IP)) {
-                slave = bond->curr_active_slave;
+                slave = rcu_dereference(bond->curr_active_slave);
                 if (slave && slave_can_tx(slave))
                         bond_dev_queue_xmit(bond, skb, slave->dev);
                 else
@@ -3870,7 +3872,7 @@ static int bond_xmit_activebackup(struct sk_buff *skb, struct net_device *bond_d
         struct bonding *bond = netdev_priv(bond_dev);
         struct slave *slave;
 
-        slave = bond->curr_active_slave;
+        slave = rcu_dereference(bond->curr_active_slave);
         if (slave)
                 bond_dev_queue_xmit(bond, skb, slave->dev);
         else
@@ -3900,7 +3902,7 @@ static int bond_xmit_broadcast(struct sk_buff *skb, struct net_device *bond_dev)
         struct bonding *bond = netdev_priv(bond_dev);
         struct slave *slave = NULL;
 
-        bond_for_each_slave(bond, slave) {
+        bond_for_each_slave_rcu(bond, slave) {
                 if (bond_is_last_slave(bond, slave))
                         break;
                 if (IS_UP(slave->dev) && slave->link == BOND_LINK_UP) {
@@ -3955,7 +3957,7 @@ static inline int bond_slave_override(struct bonding *bond,
                 return 1;
 
         /* Find out if any slaves have the same mapping as this skb. */
-        bond_for_each_slave(bond, check_slave) {
+        bond_for_each_slave_rcu(bond, check_slave) {
                 if (check_slave->queue_id == skb->queue_mapping) {
                         slave = check_slave;
                         break;
@@ -4040,14 +4042,12 @@ static netdev_tx_t bond_start_xmit(struct sk_buff *skb, struct net_device *dev)
         if (is_netpoll_tx_blocked(dev))
                 return NETDEV_TX_BUSY;
 
-        read_lock(&bond->lock);
-
+        rcu_read_lock();
         if (!list_empty(&bond->slave_list))
                 ret = __bond_start_xmit(skb, dev);
         else
                 kfree_skb(skb);
-
-        read_unlock(&bond->lock);
+        rcu_read_unlock();
 
         return ret;
 }
diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
index 0702e917d478..0f539de640dc 100644
--- a/drivers/net/bonding/bond_sysfs.c
+++ b/drivers/net/bonding/bond_sysfs.c
@@ -1243,16 +1243,16 @@ static ssize_t bonding_show_active_slave(struct device *d,
                                          struct device_attribute *attr,
                                          char *buf)
 {
-        struct slave *curr;
         struct bonding *bond = to_bond(d);
+        struct slave *curr;
         int count = 0;
 
-        read_lock(&bond->curr_slave_lock);
-        curr = bond->curr_active_slave;
-        read_unlock(&bond->curr_slave_lock);
-
+        rcu_read_lock();
+        curr = rcu_dereference(bond->curr_active_slave);
         if (USES_PRIMARY(bond->params.mode) && curr)
                 count = sprintf(buf, "%s\n", curr->dev->name);
+        rcu_read_unlock();
+
         return count;
 }
 
@@ -1284,7 +1284,7 @@ static ssize_t bonding_store_active_slave(struct device *d,
         if (!strlen(ifname) || buf[0] == '\n') {
                 pr_info("%s: Clearing current active slave.\n",
                         bond->dev->name);
-                bond->curr_active_slave = NULL;
+                rcu_assign_pointer(bond->curr_active_slave, NULL);
                 bond_select_active_slave(bond);
                 goto out;
         }
@@ -1347,14 +1347,9 @@ static ssize_t bonding_show_mii_status(struct device *d,
                                        struct device_attribute *attr,
                                        char *buf)
 {
-        struct slave *curr;
         struct bonding *bond = to_bond(d);
 
-        read_lock(&bond->curr_slave_lock);
-        curr = bond->curr_active_slave;
-        read_unlock(&bond->curr_slave_lock);
-
-        return sprintf(buf, "%s\n", curr ? "up" : "down");
+        return sprintf(buf, "%s\n", bond->curr_active_slave ? "up" : "down");
 }
 static DEVICE_ATTR(mii_status, S_IRUGO, bonding_show_mii_status, NULL);
 
diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
index 0995974c71ac..4bf52d5f637e 100644
--- a/drivers/net/bonding/bonding.h
+++ b/drivers/net/bonding/bonding.h
@@ -116,6 +116,10 @@
 #define bond_for_each_slave(bond, pos) \
         list_for_each_entry(pos, &(bond)->slave_list, list)
 
+/* Caller must have rcu_read_lock */
+#define bond_for_each_slave_rcu(bond, pos) \
+        list_for_each_entry_rcu(pos, &(bond)->slave_list, list)
+
 /**
  * bond_for_each_slave_reverse - iterate in reverse from a given position
  * @bond:       the bond holding this list