netdev - [PATCH bpf v3] xdp: fix hang while unregistering device bound to xdp socket

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Date:   Mon, 10 Jun 2019 19:15:46 +0300
From:   Ilya Maximets <i.maximets@...sung.com>
To:     netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        xdp-newbies@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Ilya Maximets <i.maximets@...sung.com>
Subject: [PATCH bpf v3] xdp: fix hang while unregistering device bound to
 xdp socket

Device that bound to XDP socket will not have zero refcount until the
userspace application will not close it. This leads to hang inside
'netdev_wait_allrefs()' if device unregistering requested:

  # ip link del p1
  < hang on recvmsg on netlink socket >

  # ps -x | grep ip
  5126  pts/0    D+   0:00 ip link del p1

  # journalctl -b

  Jun 05 07:19:16 kernel:
  unregister_netdevice: waiting for p1 to become free. Usage count = 1

  Jun 05 07:19:27 kernel:
  unregister_netdevice: waiting for p1 to become free. Usage count = 1
  ...

Fix that by implementing NETDEV_UNREGISTER event notification handler
to properly clean up all the resources and unref device.

This should also allow socket killing via ss(8) utility.

Fixes: 965a99098443 ("xsk: add support for bind for Rx")
Signed-off-by: Ilya Maximets <i.maximets@...sung.com>
---

Version 3:

    * Declaration lines ordered from longest to shortest.
    * Checking of event type moved to the top to avoid unnecessary
      locking.

Version 2:

    * Completely re-implemented using netdev event handler.

 net/xdp/xsk.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index a14e8864e4fa..273a419a8c4d 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -693,6 +693,57 @@ static int xsk_mmap(struct file *file, struct socket *sock,
 			       size, vma->vm_page_prot);
 }
 
+static int xsk_notifier(struct notifier_block *this,
+			unsigned long msg, void *ptr)
+{
+	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+	struct net *net = dev_net(dev);
+	int i, unregister_count = 0;
+	struct sock *sk;
+
+	switch (msg) {
+	case NETDEV_UNREGISTER:
+		mutex_lock(&net->xdp.lock);
+		sk_for_each(sk, &net->xdp.list) {
+			struct xdp_sock *xs = xdp_sk(sk);
+
+			mutex_lock(&xs->mutex);
+			if (dev != xs->dev) {
+				mutex_unlock(&xs->mutex);
+				continue;
+			}
+
+			sk->sk_err = ENETDOWN;
+			if (!sock_flag(sk, SOCK_DEAD))
+				sk->sk_error_report(sk);
+
+			/* Wait for driver to stop using the xdp socket. */
+			xdp_del_sk_umem(xs->umem, xs);
+			xs->dev = NULL;
+			synchronize_net();
+
+			/* Clear device references in umem. */
+			xdp_put_umem(xs->umem);
+			xs->umem = NULL;
+
+			mutex_unlock(&xs->mutex);
+			unregister_count++;
+		}
+		mutex_unlock(&net->xdp.lock);
+
+		if (unregister_count) {
+			/* Wait for umem clearing completion. */
+			synchronize_net();
+			for (i = 0; i < unregister_count; i++)
+				dev_put(dev);
+		}
+
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
 static struct proto xsk_proto = {
 	.name =		"XDP",
 	.owner =	THIS_MODULE,
@@ -727,7 +778,8 @@ static void xsk_destruct(struct sock *sk)
 	if (!sock_flag(sk, SOCK_DEAD))
 		return;
 
-	xdp_put_umem(xs->umem);
+	if (xs->umem)
+		xdp_put_umem(xs->umem);
 
 	sk_refcnt_debug_dec(sk);
 }
@@ -784,6 +836,10 @@ static const struct net_proto_family xsk_family_ops = {
 	.owner	= THIS_MODULE,
 };
 
+static struct notifier_block xsk_netdev_notifier = {
+	.notifier_call	= xsk_notifier,
+};
+
 static int __net_init xsk_net_init(struct net *net)
 {
 	mutex_init(&net->xdp.lock);
@@ -816,8 +872,15 @@ static int __init xsk_init(void)
 	err = register_pernet_subsys(&xsk_net_ops);
 	if (err)
 		goto out_sk;
+
+	err = register_netdevice_notifier(&xsk_netdev_notifier);
+	if (err)
+		goto out_pernet;
+
 	return 0;
 
+out_pernet:
+	unregister_pernet_subsys(&xsk_net_ops);
 out_sk:
 	sock_unregister(PF_XDP);
 out_proto:
-- 
2.17.1