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 counting XDP references for the device and failing
RTM_DELLINK with EBUSY if device is still in use by any XDP socket.
With this change:
# ip link del p1
RTNETLINK answers: Device or resource busy
Fixes: 965a99098443 ("xsk: add support for bind for Rx")
Signed-off-by: Ilya Maximets <[email protected]>
---
Another option could be to force closing all the corresponding AF_XDP
sockets, but I didn't figure out how to do this properly yet.
include/linux/netdevice.h | 25 +++++++++++++++++++++++++
net/core/dev.c | 10 ++++++++++
net/core/rtnetlink.c | 6 ++++++
net/xdp/xsk.c | 7 ++++++-
4 files changed, 47 insertions(+), 1 deletion(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 44b47e9df94a..24451cfc5590 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1705,6 +1705,7 @@ enum netdev_priv_flags {
* @watchdog_timer: List of timers
*
* @pcpu_refcnt: Number of references to this device
+ * @pcpu_xdp_refcnt: Number of XDP socket references to this device
* @todo_list: Delayed register/unregister
* @link_watch_list: XXX: need comments on this one
*
@@ -1966,6 +1967,7 @@ struct net_device {
struct timer_list watchdog_timer;
int __percpu *pcpu_refcnt;
+ int __percpu *pcpu_xdp_refcnt;
struct list_head todo_list;
struct list_head link_watch_list;
@@ -2636,6 +2638,7 @@ static inline void unregister_netdevice(struct net_device
*dev)
}
int netdev_refcnt_read(const struct net_device *dev);
+int netdev_xdp_refcnt_read(const struct net_device *dev);
void free_netdev(struct net_device *dev);
void netdev_freemem(struct net_device *dev);
void synchronize_net(void);
@@ -3739,6 +3742,28 @@ static inline void dev_hold(struct net_device *dev)
this_cpu_inc(*dev->pcpu_refcnt);
}
+/**
+ * dev_put_xdp - release xdp reference to device
+ * @dev: network device
+ *
+ * Decrease the reference counter of XDP sockets bound to device.
+ */
+static inline void dev_put_xdp(struct net_device *dev)
+{
+ this_cpu_dec(*dev->pcpu_xdp_refcnt);
+}
+
+/**
+ * dev_hold_xdp - get xdp reference to device
+ * @dev: network device
+ *
+ * Increase the reference counter of XDP sockets bound to device.
+ */
+static inline void dev_hold_xdp(struct net_device *dev)
+{
+ this_cpu_inc(*dev->pcpu_xdp_refcnt);
+}
+
/* Carrier loss detection, dial on demand. The functions netif_carrier_on
* and _off may be called from IRQ context, but it is caller
* who is responsible for serialization of these calls.
diff --git a/net/core/dev.c b/net/core/dev.c
index 66f7508825bd..f6f7cf3d8e93 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8840,6 +8840,16 @@ int netdev_refcnt_read(const struct net_device *dev)
}
EXPORT_SYMBOL(netdev_refcnt_read);
+int netdev_xdp_refcnt_read(const struct net_device *dev)
+{
+ int i, refcnt = 0;
+
+ for_each_possible_cpu(i)
+ refcnt += *per_cpu_ptr(dev->pcpu_xdp_refcnt, i);
+ return refcnt;
+}
+EXPORT_SYMBOL(netdev_xdp_refcnt_read);
+
/**
* netdev_wait_allrefs - wait until all references are gone.
* @dev: target net_device
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index adcc045952c2..f88bf52d41b3 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2777,6 +2777,9 @@ static int rtnl_group_dellink(const struct net *net, int
group)
ops = dev->rtnl_link_ops;
if (!ops || !ops->dellink)
return -EOPNOTSUPP;
+
+ if (netdev_xdp_refcnt_read(dev))
+ return -EBUSY;
}
}
@@ -2805,6 +2808,9 @@ int rtnl_delete_link(struct net_device *dev)
if (!ops || !ops->dellink)
return -EOPNOTSUPP;
+ if (netdev_xdp_refcnt_read(dev))
+ return -EBUSY;
+
ops->dellink(dev, &list_kill);
unregister_netdevice_many(&list_kill);
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index a14e8864e4fa..215cc8712b8d 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -361,6 +361,7 @@ static int xsk_release(struct socket *sock)
xdp_del_sk_umem(xs->umem, xs);
xs->dev = NULL;
synchronize_net();
+ dev_put_xdp(dev);
dev_put(dev);
}
@@ -423,6 +424,8 @@ static int xsk_bind(struct socket *sock, struct sockaddr
*addr, int addr_len)
goto out_release;
}
+ dev_hold_xdp(dev);
+
if (!xs->rx && !xs->tx) {
err = -EINVAL;
goto out_unlock;
@@ -490,8 +493,10 @@ static int xsk_bind(struct socket *sock, struct sockaddr
*addr, int addr_len)
xdp_add_sk_umem(xs->umem, xs);
out_unlock:
- if (err)
+ if (err) {
+ dev_put_xdp(dev);
dev_put(dev);
+ }
out_release:
mutex_unlock(&xs->mutex);
return err;
--
2.17.1
