[PATCH net-next v2 5/6] net: devmem: resolve physical map_dev for leased RX bindings

[Mina Almasry <almasrymina@google.com>]

Previously, netdev_nl_bind_rx_doit() passed netdev as both map_dev and
bind_dev to net_devmem_bind_dmabuf(), so leased RX bindings stored the
virtual netdev in binding->map_dev without tracking the physical backing
netdev at all. Unregistering the physical backing netdev while a leased
RX binding was active failed to detach and unmap the dmabuf.

Return the physical backing net_device from netdev_nl_get_dma_dev() when
the RX queue is leased from another netdev, lock map_dev around
net_devmem_bind_dmabuf() when map_dev != netdev (matching
netdev_nl_bind_tx_doit()), and assert in net_devmem_bind_dmabuf() that
both bind_dev and map_dev are locked.

Because a leased map_dev is reached via rxq->lease->dev and locked with
raw netdev_lock(map_dev) rather than netdev_get_by_index_lock(), it may
already have entered NETREG_UNREGISTERING and completed
net_devmem_dev_unregister(map_dev) before cascaded unregistration of
bind_dev tears down the lease. Reject binding in
net_devmem_bind_dmabuf() if map_dev->reg_state != NETREG_REGISTERED.

Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 net/core/devmem.c      | 12 ++++++++++++
 net/core/netdev-genl.c | 19 ++++++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index bb785a871d1c4..2dac581a57e13 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -321,6 +321,18 @@ net_devmem_bind_dmabuf(struct net_device *map_dev,
 	size_t i;
 	long err;
 
+	netdev_assert_locked(bind_dev);
+	netdev_assert_locked(map_dev);
+
+	/* When map_dev != bind_dev, map_dev is locked via the queue lease
+	 * rather than netdev_get_by_index_lock(), so it may already be
+	 * unregistering before cascaded bind_dev unregistration runs.
+	 */
+	if (map_dev->reg_state != NETREG_REGISTERED) {
+		NL_SET_ERR_MSG(extack, "Device is being unregistered");
+		return ERR_PTR(-ENODEV);
+	}
+
 	if (!dma_dev) {
 		NL_SET_ERR_MSG(extack, "Device doesn't support DMA");
 		return ERR_PTR(-EOPNOTSUPP);
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 9e56c26fc65f9..442362f23fe88 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -1005,12 +1005,15 @@ static int netdev_nl_read_rxq_bitmap(struct genl_info *info,
 
 static struct device *
 netdev_nl_get_dma_dev(struct net_device *netdev, unsigned long *rxq_bitmap,
+		      struct net_device **map_dev,
 		      struct netlink_ext_ack *extack)
 {
 	struct device *dma_dev = NULL;
 	u32 rxq_idx, prev_rxq_idx;
 
+	*map_dev = netdev;
 	for_each_set_bit(rxq_idx, rxq_bitmap, netdev->real_num_rx_queues) {
+		struct netdev_rx_queue *rxq;
 		struct device *rxq_dma_dev;
 
 		rxq_dma_dev = netdev_queue_get_dma_dev(netdev, rxq_idx,
@@ -1023,6 +1026,11 @@ netdev_nl_get_dma_dev(struct net_device *netdev, unsigned long *rxq_bitmap,
 
 		dma_dev = rxq_dma_dev;
 		prev_rxq_idx = rxq_idx;
+		if (netif_rxq_is_leased(netdev, rxq_idx) &&
+		    netif_is_queue_leasee(netdev)) {
+			rxq = __netif_get_rx_queue(netdev, rxq_idx);
+			*map_dev = rxq->lease->dev;
+		}
 	}
 
 	return dma_dev;
@@ -1032,9 +1040,9 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 {
 	struct net_devmem_dmabuf_binding *binding;
 	unsigned int niov_shift = PAGE_SHIFT;
+	struct net_device *netdev, *map_dev;
 	u32 ifindex, dmabuf_fd, rxq_idx;
 	struct netdev_nl_sock *priv;
-	struct net_device *netdev;
 	unsigned long *rxq_bitmap;
 	struct device *dma_dev;
 	struct sk_buff *rsp;
@@ -1104,16 +1112,21 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 	if (err)
 		goto err_rxq_bitmap;
 
-	dma_dev = netdev_nl_get_dma_dev(netdev, rxq_bitmap, info->extack);
+	dma_dev = netdev_nl_get_dma_dev(netdev, rxq_bitmap, &map_dev,
+					info->extack);
 	if (IS_ERR(dma_dev)) {
 		err = PTR_ERR(dma_dev);
 		goto err_rxq_bitmap;
 	}
 
-	binding = net_devmem_bind_dmabuf(netdev, netdev, dma_dev,
+	if (map_dev != netdev)
+		netdev_lock(map_dev);
+	binding = net_devmem_bind_dmabuf(map_dev, netdev, dma_dev,
 					 DMA_FROM_DEVICE, dmabuf_fd,
 					 niov_shift, priv, NETLINK_CB(skb).sk,
 					 info->extack);
+	if (map_dev != netdev)
+		netdev_unlock(map_dev);
 	if (IS_ERR(binding)) {
 		err = PTR_ERR(binding);
 		goto err_rxq_bitmap;
-- 
2.56.0.455.g6c5a503b38-goog