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[5.12.227.87]) by smtp.gmail.com with ESMTPSA id h16sm4776714eji.110.2021.01.09.09.27.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 09 Jan 2021 09:27:41 -0800 (PST) From: Vladimir Oltean To: "David S . Miller" , Jakub Kicinski Cc: netdev@vger.kernel.org, Andrew Lunn , Florian Fainelli , Cong Wang , Stephen Hemminger , Eric Dumazet , George McCollister , Oleksij Rempel , Jay Vosburgh , Veaceslav Falico , Andy Gospodarek , Arnd Bergmann , Taehee Yoo , Jiri Pirko , Florian Westphal , Nikolay Aleksandrov , Pravin B Shelar , Sridhar Samudrala , Saeed Mahameed Subject: [PATCH v6 net-next 13/15] net: net_failover: ensure .ndo_get_stats64 can sleep Date: Sat, 9 Jan 2021 19:26:22 +0200 Message-Id: <20210109172624.2028156-14-olteanv@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210109172624.2028156-1-olteanv@gmail.com> References: <20210109172624.2028156-1-olteanv@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org From: Vladimir Oltean 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 is ok because it is reentrant, and generally speaking, dev_get_stats is recursive. But it is also not ok, because holding rcu_read_lock() while calling dev_get_stats will incur atomic context upon it, and that needs to change. The existing logic can be rehashed just a little bit such that the recursive dev_get_stats call will not be under any lock. We can achieve that by "cheating" a little bit and use dev_hold() to take a reference on the active and backup interfaces, and netdev_wait_allrefs() will just have to wait until dev_get_stats() finishes. Signed-off-by: Vladimir Oltean --- Changes in v6: Slightly touch up the commit message. Changes in v5: Use rcu_read_lock() and do not change the locking architecture of the driver. Changes in v4: Now there is code to propagate errors. Changes in v3: None. Changes in v2: Switched to the new scheme of holding just a refcnt to the slave interfaces while recursing with dev_get_stats. drivers/net/net_failover.c | 64 ++++++++++++++++++++++++++++---------- 1 file changed, 47 insertions(+), 17 deletions(-) diff --git a/drivers/net/net_failover.c b/drivers/net/net_failover.c index 2815228a34d5..8b7a6d1eab30 100644 --- a/drivers/net/net_failover.c +++ b/drivers/net/net_failover.c @@ -183,38 +183,64 @@ static int 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; int err = 0; - spin_lock(&nfo_info->stats_lock); - memcpy(stats, &nfo_info->failover_stats, sizeof(*stats)); - rcu_read_lock(); - slave_dev = rcu_dereference(nfo_info->primary_dev); - if (slave_dev) { - err = dev_get_stats(slave_dev, &temp); + primary_dev = rcu_dereference(nfo_info->primary_dev); + if (primary_dev) + dev_hold(primary_dev); + + standby_dev = rcu_dereference(nfo_info->standby_dev); + if (standby_dev) + dev_hold(standby_dev); + + rcu_read_unlock(); + + /* Don't hold rcu_read_lock while calling dev_get_stats, just a + * reference to ensure they won't get unregistered. + */ + if (primary_dev) { + err = dev_get_stats(primary_dev, &primary_stats); if (err) goto out; - net_failover_fold_stats(stats, &temp, &nfo_info->primary_stats); - memcpy(&nfo_info->primary_stats, &temp, sizeof(temp)); } - slave_dev = rcu_dereference(nfo_info->standby_dev); - if (slave_dev) { - err = dev_get_stats(slave_dev, &temp); + if (standby_dev) { + err = dev_get_stats(standby_dev, &standby_stats); if (err) goto out; - net_failover_fold_stats(stats, &temp, &nfo_info->standby_stats); - memcpy(&nfo_info->standby_stats, &temp, sizeof(temp)); } -out: - rcu_read_unlock(); + spin_lock(&nfo_info->stats_lock); + + memcpy(stats, &nfo_info->failover_stats, sizeof(*stats)); + + if (primary_dev) { + net_failover_fold_stats(stats, &primary_stats, + &nfo_info->primary_stats); + memcpy(&nfo_info->primary_stats, &primary_stats, + sizeof(primary_stats)); + } + if (standby_dev) { + 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); +out: + if (primary_dev) + dev_put(primary_dev); + if (standby_dev) + dev_put(standby_dev); return err; } @@ -728,6 +754,7 @@ 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; @@ -772,6 +799,9 @@ 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); + spin_lock_init(&nfo_info->stats_lock); + err = register_netdev(failover_dev); if (err) { dev_err(dev, "Unable to register failover_dev!\n");