[PATCH 5.10 010/105] net: make free_netdev() more lenient with unregistering devices

Greg Kroah-Hartman
2022-07-27T16:47:55Z

From: Fedor Pchelkin <pchelkin@ispras.ru>

From: Jakub Kicinski <kuba@kernel.org>

commit c269a24ce057abfc31130960e96ab197ef6ab196 upstream.

There are two flavors of handling netdev registration:
- ones called without holding rtnl_lock: register_netdev() and
unregister_netdev(); and
- those called with rtnl_lock held: register_netdevice() and
unregister_netdevice().

While the semantics of the former are pretty clear, the same can't
be said about the latter. The netdev_todo mechanism is utilized to
perform some of the device unregistering tasks and it hooks into
rtnl_unlock() so the locked variants can't actually finish the work.
In general free_netdev() does not mix well with locked calls. Most
drivers operating under rtnl_lock set dev->needs_free_netdev to true
and expect core to make the free_netdev() call some time later.

The part where this becomes most problematic is error paths. There is
no way to unwind the state cleanly after a call to register_netdevice(),
since unreg can't be performed fully without dropping locks.

Make free_netdev() more lenient, and defer the freeing if device
is being unregistered. This allows error paths to simply call
free_netdev() both after register_netdevice() failed, and after
a call to unregister_netdevice() but before dropping rtnl_lock.

Simplify the error paths which are currently doing gymnastics
around free_netdev() handling.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/8021q/vlan.c | 4 +---
net/core/dev.c | 11 +++++++++++
net/core/rtnetlink.c | 23 ++++++-----------------
3 files changed, 18 insertions(+), 20 deletions(-)

--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -278,9 +278,7 @@ static int register_vlan_device(struct n
return 0;

out_free_newdev:
- if (new_dev->reg_state == NETREG_UNINITIALIZED ||
- new_dev->reg_state == NETREG_UNREGISTERED)
- free_netdev(new_dev);
+ free_netdev(new_dev);
return err;
}

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10683,6 +10683,17 @@ void free_netdev(struct net_device *dev)
struct napi_struct *p, *n;

might_sleep();
+
+ /* When called immediately after register_netdevice() failed the unwind
+ * handling may still be dismantling the device. Handle that case by
+ * deferring the free.
+ */
+ if (dev->reg_state == NETREG_UNREGISTERING) {
+ ASSERT_RTNL();
+ dev->needs_free_netdev = true;
+ return;
+ }
+
netif_free_tx_queues(dev);
netif_free_rx_queues(dev);

--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3442,26 +3442,15 @@ replay:

dev->ifindex = ifm->ifi_index;

- if (ops->newlink) {
+ if (ops->newlink)
err = ops->newlink(link_net ? : net, dev, tb, data, extack);
- /* Drivers should set dev->needs_free_netdev
- * and unregister it on failure after registration
- * so that device could be finally freed in rtnl_unlock.
- */
- if (err < 0) {
- /* If device is not registered at all, free it now */
- if (dev->reg_state == NETREG_UNINITIALIZED ||
- dev->reg_state == NETREG_UNREGISTERED)
- free_netdev(dev);
- goto out;
- }
- } else {
+ else
err = register_netdevice(dev);
- if (err < 0) {
- free_netdev(dev);
- goto out;
- }
+ if (err < 0) {
+ free_netdev(dev);
+ goto out;
}
+
err = rtnl_configure_link(dev, ifm);
if (err < 0)
goto out_unregister;