[PATCH net-next v2 3/6] net: guard memory provider RX queue open and close on unregister

[Mina Almasry <almasrymina@google.com>]

When a memory provider RX queue is leased to a virtual netdev,
netif_mp_open_rxq() and netif_mp_close_rxq() redirect through
rxq->lease and lock the physical backing netdev directly rather than via
netdev_get_by_index_lock(). This raises two issues during netdev
unregistration:

1. In __netif_mp_open_rxq(), the physical backing netdev may already be
   in NETREG_UNREGISTERING (after dev_shutdown() and
   dev_memory_provider_uninstall() have run on it, before cascaded
   unregistration of the virtual leasee tears down the lease). Reject
   opening an RX queue if dev->reg_state != NETREG_REGISTERED.
2. In __netif_mp_close_rxq(), when the physical backing netdev
   unregisters before the virtual leasee, dev_memory_provider_uninstall()
   on the physical netdev does not uninstall the virtual queues, so
   phys_rxq->mp_params remains populated until the virtual leasee's
   netif_rxq_cleanup_unlease() or socket teardown runs. At that point
   the physical netdev has already gone through dev_shutdown() and must
   not call netdev_rx_queue_reconfig(). When dev->reg_state >
   NETREG_REGISTERED, clear rxq->mp_params and return 0.

Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 net/core/netdev_rx_queue.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/net/core/netdev_rx_queue.c b/net/core/netdev_rx_queue.c
index a7261fedd5e76..85ae5abf16b8e 100644
--- a/net/core/netdev_rx_queue.c
+++ b/net/core/netdev_rx_queue.c
@@ -193,6 +193,14 @@ static int __netif_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx,
 	struct netdev_rx_queue *rxq;
 	int ret;
 
+	/* A leased physical dev is locked via rxq->lease rather than
+	 * netdev_get_by_index_lock(), so check reg_state under its lock.
+	 */
+	if (dev->reg_state != NETREG_REGISTERED) {
+		NL_SET_ERR_MSG(extack, "Device is being unregistered");
+		return -ENODEV;
+	}
+
 	if (!qops)
 		return -EOPNOTSUPP;
 
@@ -284,12 +292,13 @@ static int __netif_mp_close_rxq(struct net_device *dev, unsigned int rxq_idx,
 
 	rxq = __netif_get_rx_queue(dev, rxq_idx);
 
-	/* Callers holding a netdev ref may get here after we already
-	 * went thru shutdown via dev_memory_provider_uninstall().
+	/* Callers holding a netdev ref or tearing down a queue lease may get
+	 * here after dev already went through shutdown.
 	 */
-	if (dev->reg_state > NETREG_REGISTERED &&
-	    !rxq->mp_params.mp_ops)
+	if (dev->reg_state > NETREG_REGISTERED) {
+		memset(&rxq->mp_params, 0, sizeof(rxq->mp_params));
 		return 0;
+	}
 
 	if (WARN_ON_ONCE(rxq->mp_params.mp_ops != old_p->mp_ops ||
 			 rxq->mp_params.mp_priv != old_p->mp_priv))
-- 
2.56.0.455.g6c5a503b38-goog