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From 11fd667dac315ea3f2469961f6d2869271a46cae Mon Sep 17 00:00:00 2001
From: Vladimir Oltean <vladimir.oltean@nxp.com>
Date: Thu, 6 Jan 2022 01:11:17 +0200
Subject: [PATCH 6/6] net: dsa: setup master before ports
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>
---
net/dsa/dsa2.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -545,6 +545,7 @@ static void dsa_port_teardown(struct dsa
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;
@@ -566,9 +567,11 @@ static void dsa_port_teardown(struct dsa
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;
}
@@ -1130,17 +1133,17 @@ static int dsa_tree_setup(struct dsa_swi
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;
@@ -1148,10 +1151,10 @@ static int dsa_tree_setup(struct dsa_swi
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:
@@ -1169,10 +1172,10 @@ static void dsa_tree_teardown(struct dsa
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);
|
