netdev - [PATCH bpf v2] xdp: fix hang while unregistering device bound to xdp socket

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Date:   Fri,  7 Jun 2019 20:31:43 +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>,
        Ilya Maximets <i.maximets@...sung.com>
Subject: [PATCH bpf v2] 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>
---
 net/xdp/xsk.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 61 insertions(+), 1 deletion(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index a14e8864e4fa..3f3979579d21 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -693,6 +693,54 @@ 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 sock *sk;
+	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+	struct net *net = dev_net(dev);
+	int i, unregister_count = 0;
+
+	mutex_lock(&net->xdp.lock);
+	sk_for_each(sk, &net->xdp.list) {
+		struct xdp_sock *xs = xdp_sk(sk);
+
+		mutex_lock(&xs->mutex);
+		switch (msg) {
+		case NETDEV_UNREGISTER:
+			if (dev != xs->dev)
+				break;
+
+			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;
+
+			unregister_count++;
+			break;
+		}
+		mutex_unlock(&xs->mutex);
+	}
+	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);
+	}
+
+	return NOTIFY_DONE;
+}
+
 static struct proto xsk_proto = {
 	.name =		"XDP",
 	.owner =	THIS_MODULE,
@@ -727,7 +775,8 @@ 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 +833,10 @@ 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 +869,15 @@ 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