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net: dsa: setup master before ports

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It is said that as soon as a network interface is registered, all its
resources should have already been prepared, so that it is available for
sending and receiving traffic. One of the resources needed by a DSA
slave interface is the master.

dsa_tree_setup
-> dsa_tree_setup_ports
   -> dsa_port_setup
      -> dsa_slave_create
         -> register_netdevice
-> dsa_tree_setup_master
   -> dsa_master_setup
      -> sets up master->dsa_ptr, which enables reception

Therefore, there is a short period of time after register_netdevice()
during which the master isn't prepared to pass traffic to the DSA layer
(master->dsa_ptr is checked by eth_type_trans). Same thing during
unregistration, there is a time frame in which packets might be missed.

Note that this change opens us to another race: dsa_master_find_slave()
will get invoked potentially earlier than the slave creation, and later
than the slave deletion. Since dp->slave starts off as a NULL pointer,
the earlier calls aren't a problem, but the later calls are. To avoid
use-after-free, we should zeroize dp->slave before calling
dsa_slave_destroy().

In practice I cannot really test real life improvements brought by this
change, since in my systems, netdevice creation races with PHY autoneg
which takes a few seconds to complete, and that masks quite a few races.
Effects might be noticeable in a setup with fixed links all the way to
an external system.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vladimir Oltean 2022-01-06 01:11:17 +02:00 committed by David S. Miller
parent 1e3f407f3c
commit 11fd667dac
1 changed files with 13 additions and 10 deletions
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23
net/dsa/dsa2.c
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@ -561,6 +561,7 @@ static void dsa_port_teardown(struct dsa_port *dp)
struct devlink_port *dlp = &dp->devlink_port;
struct dsa_switch *ds = dp->ds;
struct dsa_mac_addr *a, *tmp;
struct net_device *slave;
if (!dp->setup)
return;
@ -582,9 +583,11 @@ static void dsa_port_teardown(struct dsa_port *dp)
dsa_port_link_unregister_of(dp);
break;
case DSA_PORT_TYPE_USER:
if (dp->slave) {
dsa_slave_destroy(dp->slave);
slave = dp->slave;
if (slave) {
dp->slave = NULL;
dsa_slave_destroy(slave);
}
break;
}
@ -1134,17 +1137,17 @@ static int dsa_tree_setup(struct dsa_switch_tree *dst)
if (err)
goto teardown_cpu_ports;
err = dsa_tree_setup_ports(dst);
err = dsa_tree_setup_master(dst);
if (err)
goto teardown_switches;
err = dsa_tree_setup_master(dst);
err = dsa_tree_setup_ports(dst);
if (err)
goto teardown_ports;
goto teardown_master;
err = dsa_tree_setup_lags(dst);
if (err)
goto teardown_master;
goto teardown_ports;
dst->setup = true;
@ -1152,10 +1155,10 @@ static int dsa_tree_setup(struct dsa_switch_tree *dst)
return 0;
teardown_master:
dsa_tree_teardown_master(dst);
teardown_ports:
dsa_tree_teardown_ports(dst);
teardown_master:
dsa_tree_teardown_master(dst);
teardown_switches:
dsa_tree_teardown_switches(dst);
teardown_cpu_ports:
@ -1173,10 +1176,10 @@ static void dsa_tree_teardown(struct dsa_switch_tree *dst)
dsa_tree_teardown_lags(dst);
dsa_tree_teardown_master(dst);
dsa_tree_teardown_ports(dst);
dsa_tree_teardown_master(dst);
dsa_tree_teardown_switches(dst);
dsa_tree_teardown_cpu_ports(dst);