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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>
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|---|---|---|
| .. | ||
| dsa2.c | ||
| dsa_priv.h | ||
| dsa.c | ||
| Kconfig | ||
| Makefile | ||
| master.c | ||
| port.c | ||
| slave.c | ||
| switch.c | ||
| tag_8021q.c | ||
| tag_ar9331.c | ||
| tag_brcm.c | ||
| tag_dsa.c | ||
| tag_gswip.c | ||
| tag_hellcreek.c | ||
| tag_ksz.c | ||
| tag_lan9303.c | ||
| tag_mtk.c | ||
| tag_ocelot_8021q.c | ||
| tag_ocelot.c | ||
| tag_qca.c | ||
| tag_rtl4_a.c | ||
| tag_rtl8_4.c | ||
| tag_sja1105.c | ||
| tag_trailer.c | ||
| tag_xrs700x.c | ||