[PATCH] netpoll: protect napi_poll and poll_controller during dev_[open|close]

[Neil Horman <nhorman@tuxdriver.com>]

Ivan Vercera was recently backporting commit
9c13cb8bb477a83b9a3c9e5a5478a4e21294a760 to a RHEL kernel, and I noticed that,
while this patch protects the tg3 driver from having its ndo_poll_controller
routine called during device initalization, it does nothing for the driver
during shutdown. I.e. it would be entirely possible to have the
ndo_poll_controller method (or subsequently the ndo_poll) routine called for a
driver in the netpoll path on CPU A while in parallel on CPU B, the ndo_close or
ndo_open routine could be called.  Given that the two latter routines tend to
initizlize and free many data structures that the former two rely on, the result
can easily be data corruption or various other crashes.  Furthermore, it seems
that this is potentially a problem with all net drivers that support netpoll,
and so this should ideally be fixed in a common path.

Fix it by creating a spinlock in the netpoll_info structure, and holding it on
netpoll_poll_dev, and in dev_close and dev_open.  That will prevent the driver
from getting torn down while we're using it in the netpoll path

I've done some testing on this, flooding a netconsole enabled system with
messages and ifup/downing the interface. No problems observed

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Ivan Vecera <ivecera@redhat.com>
CC: "David S. Miller" <davem@davemloft.net>
---
 include/linux/netpoll.h |  1 +
 net/core/dev.c          | 16 ++++++++++++++++
 net/core/netpoll.c      |  3 +++
 3 files changed, 20 insertions(+)

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index f54c3bb..bb1d364 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -40,6 +40,7 @@ struct netpoll_info {
 
 	int rx_flags;
 	spinlock_t rx_lock;
+	spinlock_t napi_lock;
 	struct list_head rx_np; /* netpolls that registered an rx_hook */
 
 	struct sk_buff_head neigh_tx; /* list of neigh requests to reply to */
diff --git a/net/core/dev.c b/net/core/dev.c
index a87bc74..18f85e1 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1307,11 +1307,19 @@ static int __dev_open(struct net_device *dev)
 int dev_open(struct net_device *dev)
 {
 	int ret;
+	struct netpoll_info *ni;
 
 	if (dev->flags & IFF_UP)
 		return 0;
 
+	rcu_read_lock();
+	ni = rcu_dereference(dev->npinfo);
+	if (ni)
+		spin_lock(&ni->napi_lock);
 	ret = __dev_open(dev);
+	if (ni)
+		spin_unlock(&ni->napi_lock);
+	rcu_read_unlock();
 	if (ret < 0)
 		return ret;
 
@@ -1325,6 +1333,7 @@ EXPORT_SYMBOL(dev_open);
 static int __dev_close_many(struct list_head *head)
 {
 	struct net_device *dev;
+	struct netpoll_info *ni;
 
 	ASSERT_RTNL();
 	might_sleep();
@@ -1355,8 +1364,15 @@ static int __dev_close_many(struct list_head *head)
 		 *	We allow it to be called even after a DETACH hot-plug
 		 *	event.
 		 */
+		rcu_read_lock();
+		ni = rcu_dereference(dev->npinfo);
+		if (ni)
+			spin_lock(&ni->napi_lock);
 		if (ops->ndo_stop)
 			ops->ndo_stop(dev);
+		if (ni)
+			spin_unlock(&ni->napi_lock);
+		rcu_read_unlock();
 
 		dev->flags &= ~IFF_UP;
 		net_dmaengine_put();
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 331ccb9..f72eaa9 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -207,9 +207,11 @@ static void netpoll_poll_dev(struct net_device *dev)
 		return;
 
 	/* Process pending work on NIC */
+	spin_lock(&ni->napi_lock);
 	ops->ndo_poll_controller(dev);
 
 	poll_napi(dev);
+	spin_lock(&ni->napi_lock);
 
 	if (dev->flags & IFF_SLAVE) {
 		if (ni) {
@@ -1004,6 +1006,7 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev, gfp_t gfp)
 		INIT_LIST_HEAD(&npinfo->rx_np);
 
 		spin_lock_init(&npinfo->rx_lock);
+		spin_lock_init(&npinfo->napi_lock);
 		skb_queue_head_init(&npinfo->neigh_tx);
 		skb_queue_head_init(&npinfo->txq);
 		INIT_DELAYED_WORK(&npinfo->tx_work, queue_process);
-- 
1.7.11.7