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net: make free_netdev() more lenient with unregistering devices

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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>
This commit is contained in:
Jakub Kicinski 2021-01-06 10:40:06 -08:00
parent 2b446e650b
commit c269a24ce0
3 changed files with 18 additions and 20 deletions
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4
net/8021q/vlan.c
View File

@ -284,9 +284,7 @@ static int register_vlan_device(struct net_device *real_dev, u16 vlan_id)
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;
}

11
net/core/dev.c
View File

@ -10631,6 +10631,17 @@ 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);

23
net/core/rtnetlink.c
View File

@ -3439,26 +3439,15 @@ 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;