[PATCH net-next] net: revert to lockless TC_SETUP_BLOCK and TC_SETUP_FT

[Stanislav Fomichev]

There is a couple of places from which we can arrive to ndo_setup_tc
with TC_SETUP_BLOCK/TC_SETUP_FT:
- netlink
- netlink notifier
- netdev notifier

Locking netdev too deep in this call chain seems to be problematic
(especially assuming some/all of the call_netdevice_notifiers
NETDEV_UNREGISTER) might soon be running with the instance lock).
Revert to lockless ndo_setup_tc for TC_SETUP_BLOCK/TC_SETUP_FT. NFT
framework already takes care of most of the locking. Document
the assumptions.

ndo_setup_tc TC_SETUP_BLOCK
  nft_block_offload_cmd
    nft_chain_offload_cmd
      nft_flow_block_chain
        nft_flow_offload_chain
	  nft_flow_rule_offload_abort
	    nft_flow_rule_offload_commit
	  nft_flow_rule_offload_commit
	    nf_tables_commit
	      nfnetlink_rcv_batch
	        nfnetlink_rcv_skb_batch
		  nfnetlink_rcv
	nft_offload_netdev_event
	  NETDEV_UNREGISTER notifier

ndo_setup_tc TC_SETUP_FT
  nf_flow_table_offload_cmd
    nf_flow_table_offload_setup
      nft_unregister_flowtable_hook
        nft_register_flowtable_net_hooks
	  nft_flowtable_update
	  nf_tables_newflowtable
	    nfnetlink_rcv_batch (.call NFNL_CB_BATCH)
	nft_flowtable_update
	  nf_tables_newflowtable
	nft_flowtable_event
	  nf_tables_flowtable_event
	    NETDEV_UNREGISTER notifier
      __nft_unregister_flowtable_net_hooks
        nft_unregister_flowtable_net_hooks
	  nf_tables_commit
	    nfnetlink_rcv_batch (.call NFNL_CB_BATCH)
	  __nf_tables_abort
	    nf_tables_abort
	      nfnetlink_rcv_batch
	__nft_release_hook
	  __nft_release_hooks
	    nf_tables_pre_exit_net -> module unload
	  nft_rcv_nl_event
	    netlink_register_notifier (oh boy)
      nft_register_flowtable_net_hooks
      	nft_flowtable_update
	  nf_tables_newflowtable
        nf_tables_newflowtable

Fixes: c4f0f30b424e ("net: hold netdev instance lock during nft ndo_setup_tc")
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
---
 Documentation/networking/netdevices.rst |  6 ++++++
 include/linux/netdevice.h               |  2 --
 net/core/dev.c                          | 19 -------------------
 net/netfilter/nf_flow_table_offload.c   |  2 +-
 net/netfilter/nf_tables_offload.c       |  2 +-
 5 files changed, 8 insertions(+), 23 deletions(-)

diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst
index d235a7364893..ebb868f50ac2 100644
--- a/Documentation/networking/netdevices.rst
+++ b/Documentation/networking/netdevices.rst
@@ -290,6 +290,12 @@ struct net_device synchronization rules
 	Synchronization: netif_addr_lock spinlock.
 	Context: BHs disabled
 
+ndo_setup_tc:
+	``TC_SETUP_BLOCK`` and ``TC_SETUP_FT`` are running under NFT locks
+	(i.e. no ``rtnl_lock`` and no device instance lock). The rest of
+	``tc_setup_type`` types run under netdev instance lock if the driver
+	implements queue management or shaper API.
+
 Most ndo callbacks not specified in the list above are running
 under ``rtnl_lock``. In addition, netdev instance lock is taken as well if
 the driver implements queue management or shaper API.
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d206c9592b60..87fd3b1f2b99 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3395,8 +3395,6 @@ int dev_open(struct net_device *dev, struct netlink_ext_ack *extack);
 void netif_close(struct net_device *dev);
 void dev_close(struct net_device *dev);
 void dev_close_many(struct list_head *head, bool unlink);
-int dev_setup_tc(struct net_device *dev, enum tc_setup_type type,
-		 void *type_data);
 void netif_disable_lro(struct net_device *dev);
 void dev_disable_lro(struct net_device *dev);
 int dev_loopback_xmit(struct net *net, struct sock *sk, struct sk_buff *newskb);
diff --git a/net/core/dev.c b/net/core/dev.c
index a0f75a1d1f5a..8b3603b764a7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1760,25 +1760,6 @@ void netif_close(struct net_device *dev)
 	}
 }
 
-int dev_setup_tc(struct net_device *dev, enum tc_setup_type type,
-		 void *type_data)
-{
-	const struct net_device_ops *ops = dev->netdev_ops;
-	int ret;
-
-	ASSERT_RTNL();
-
-	if (!ops->ndo_setup_tc)
-		return -EOPNOTSUPP;
-
-	netdev_lock_ops(dev);
-	ret = ops->ndo_setup_tc(dev, type, type_data);
-	netdev_unlock_ops(dev);
-
-	return ret;
-}
-EXPORT_SYMBOL(dev_setup_tc);
-
 void netif_disable_lro(struct net_device *dev)
 {
 	struct net_device *lower_dev;
diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
index 0ec4abded10d..e06bc36f49fe 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -1175,7 +1175,7 @@ static int nf_flow_table_offload_cmd(struct flow_block_offload *bo,
 	nf_flow_table_block_offload_init(bo, dev_net(dev), cmd, flowtable,
 					 extack);
 	down_write(&flowtable->flow_block_lock);
-	err = dev_setup_tc(dev, TC_SETUP_FT, bo);
+	err = dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_FT, bo);
 	up_write(&flowtable->flow_block_lock);
 	if (err < 0)
 		return err;
diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c
index b761899c143c..64675f1c7f29 100644
--- a/net/netfilter/nf_tables_offload.c
+++ b/net/netfilter/nf_tables_offload.c
@@ -390,7 +390,7 @@ static int nft_block_offload_cmd(struct nft_base_chain *chain,
 
 	nft_flow_block_offload_init(&bo, dev_net(dev), cmd, chain, &extack);
 
-	err = dev_setup_tc(dev, TC_SETUP_BLOCK, &bo);
+	err = dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_BLOCK, &bo);
 	if (err < 0)
 		return err;
 
-- 
2.48.1