From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
The failover framework sets up a virtio_net interface [ when it has the
VIRTIO_NET_F_STANDBY feature ] and a VF interface, having the same MAC
address, in a standby/active relationship. When the active VF is
unplugged, the standby virtio_net temporarily kicks in.
The failover framework registers a common upper for the active and the
standby interface, which is what the application layer uses. This is
similar to bonding/team. The statistics of the upper interface are the
sum of the statistics of the active and of the standby interface.
There is an effort to convert .ndo_get_stats64 to sleepable context, and
for that to work, we need to prevent callers of dev_get_stats from using
atomic locking. The failover driver needs protection via an RCU
read-side critical section to access the standby and the active
interface. This has two features:
- It is atomic: this needs to change.
- It is reentrant: this is ok, because generally speaking, dev_get_stats
is recursive, and taking global locks is a bad thing from a recursive
context.
A better locking architecture would be to do what the team driver does.
Instead of using something as broad as the rtnl_mutex to ensure
serialization of updates, it should use something more specific, like a
private mutex. This patch adds that and names it slaves_lock. The
slaves_lock now protects the only updater, the rcu_assign_pointer
sections from net_failover_slave_register.
In the team driver, a separate lockdep class is created for each team
lock, to account for possible nesting (team over team over ...). For the
net_failover driver, we can do something simpler, which is to just not
hold any lock while we call dev_get_stats recursively. We can "cheat"
and use dev_hold to take a reference on the active and backup interfaces,
and netdev_wait_allrefs() will just have to wait until we finish.
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
drivers/net/net_failover.c | 62 +++++++++++++++++++++++++++-----------
include/net/net_failover.h | 9 ++++--
2 files changed, 52 insertions(+), 19 deletions(-)
diff --git a/drivers/net/net_failover.c b/drivers/net/net_failover.c
index 4f83165412bd..c83066b0ef70 100644
--- a/drivers/net/net_failover.c
+++ b/drivers/net/net_failover.c
@@ -27,6 +27,9 @@
#include <uapi/linux/if_arp.h>
#include <net/net_failover.h>
+#define nfo_dereference(nfo_info, p) \
+ rcu_dereference_protected(p, lockdep_is_held(&nfo_info->slaves_lock))
+
static bool net_failover_xmit_ready(struct net_device *dev)
{
return netif_running(dev) && netif_carrier_ok(dev);
@@ -183,32 +186,48 @@ static void net_failover_get_stats(struct net_device *dev,
struct rtnl_link_stats64 *stats)
{
struct net_failover_info *nfo_info = netdev_priv(dev);
- struct rtnl_link_stats64 temp;
- struct net_device *slave_dev;
+ struct rtnl_link_stats64 primary_stats;
+ struct rtnl_link_stats64 standby_stats;
+ struct net_device *primary_dev;
+ struct net_device *standby_dev;
- spin_lock(&nfo_info->stats_lock);
- memcpy(stats, &nfo_info->failover_stats, sizeof(*stats));
+ mutex_lock(&nfo_info->slaves_lock);
- rcu_read_lock();
+ primary_dev = nfo_dereference(nfo_info, nfo_info->primary_dev);
+ if (primary_dev)
+ dev_hold(primary_dev);
- slave_dev = rcu_dereference(nfo_info->primary_dev);
- if (slave_dev) {
- dev_get_stats(slave_dev, &temp);
- net_failover_fold_stats(stats, &temp, &nfo_info->primary_stats);
- memcpy(&nfo_info->primary_stats, &temp, sizeof(temp));
+ standby_dev = nfo_dereference(nfo_info, nfo_info->standby_dev);
+ if (standby_dev)
+ dev_hold(standby_dev);
+
+ mutex_unlock(&nfo_info->slaves_lock);
+
+ /* Don't hold slaves_lock while calling dev_get_stats, just a
+ * reference to ensure they won't get unregistered.
+ */
+ if (primary_dev) {
+ dev_get_stats(primary_dev, &primary_stats);
+ dev_put(primary_dev);
}
- slave_dev = rcu_dereference(nfo_info->standby_dev);
- if (slave_dev) {
- dev_get_stats(slave_dev, &temp);
- net_failover_fold_stats(stats, &temp, &nfo_info->standby_stats);
- memcpy(&nfo_info->standby_stats, &temp, sizeof(temp));
+ if (standby_dev) {
+ dev_get_stats(standby_dev, &standby_stats);
+ dev_put(standby_dev);
}
- rcu_read_unlock();
+ mutex_lock(&nfo_info->stats_lock);
+
+ memcpy(stats, &nfo_info->failover_stats, sizeof(*stats));
+
+ net_failover_fold_stats(stats, &primary_stats, &nfo_info->primary_stats);
+ memcpy(&nfo_info->primary_stats, &primary_stats, sizeof(primary_stats));
+ net_failover_fold_stats(stats, &standby_stats, &nfo_info->standby_stats);
+ memcpy(&nfo_info->standby_stats, &standby_stats, sizeof(standby_stats));
memcpy(&nfo_info->failover_stats, stats, sizeof(*stats));
- spin_unlock(&nfo_info->stats_lock);
+
+ mutex_unlock(&nfo_info->stats_lock);
}
static int net_failover_change_mtu(struct net_device *dev, int new_mtu)
@@ -540,6 +559,8 @@ static int net_failover_slave_register(struct net_device *slave_dev,
primary_dev = rtnl_dereference(nfo_info->primary_dev);
slave_is_standby = slave_dev->dev.parent == failover_dev->dev.parent;
+ mutex_lock(&nfo_info->slaves_lock);
+
if (slave_is_standby) {
rcu_assign_pointer(nfo_info->standby_dev, slave_dev);
standby_dev = slave_dev;
@@ -552,6 +573,8 @@ static int net_failover_slave_register(struct net_device *slave_dev,
failover_dev->max_mtu = slave_dev->max_mtu;
}
+ mutex_unlock(&nfo_info->slaves_lock);
+
net_failover_lower_state_changed(slave_dev, primary_dev, standby_dev);
net_failover_compute_features(failover_dev);
@@ -709,6 +732,7 @@ static struct failover_ops net_failover_ops = {
struct failover *net_failover_create(struct net_device *standby_dev)
{
struct device *dev = standby_dev->dev.parent;
+ struct net_failover_info *nfo_info;
struct net_device *failover_dev;
struct failover *failover;
int err;
@@ -753,6 +777,10 @@ struct failover *net_failover_create(struct net_device *standby_dev)
failover_dev->min_mtu = standby_dev->min_mtu;
failover_dev->max_mtu = standby_dev->max_mtu;
+ nfo_info = netdev_priv(failover_dev);
+ mutex_init(&nfo_info->slaves_lock);
+ mutex_init(&nfo_info->stats_lock);
+
err = register_netdev(failover_dev);
if (err) {
dev_err(dev, "Unable to register failover_dev!\n");
diff --git a/include/net/net_failover.h b/include/net/net_failover.h
index b12a1c469d1c..988cdfaf14ca 100644
--- a/include/net/net_failover.h
+++ b/include/net/net_failover.h
@@ -23,8 +23,13 @@ struct net_failover_info {
/* aggregated stats */
struct rtnl_link_stats64 failover_stats;
- /* spinlock while updating stats */
- spinlock_t stats_lock;
+ /* lock for updating stats */
+ struct mutex stats_lock;
+
+ /* lock for protecting lower interfaces.
+ * TODO: convert all rtnl_dereference instances to nfo_dereference
+ */
+ struct mutex slaves_lock;
};
struct failover *net_failover_create(struct net_device *standby_dev);
--
2.25.1
