On RZ/G3S SMARC Carrier II board having RGMII connections b/w Ethernet
MACs and PHYs it has been discovered that doing unbind/bind for ravb
driver in a loop leads to wrong speed and duplex for Ethernet links and
broken connectivity (the connectivity cannot be restored even with
bringing interface down/up). Before doing unbind/bind the Ethernet
interfaces were configured though systemd. The sh instructions used to
do unbind/bind were:

$ cd /sys/bus/platform/drivers/ravb/
$ while :; do echo 11c30000.ethernet > unbind ; \
  echo 11c30000.ethernet > bind; done

It has been discovered that there is a race b/w IOCTLs initialized by
systemd at the response of success binding and the
"ravb_write(ndev, CCC_OPC_RESET, CCC)" call in ravb_remove() as
follows:

1/ as a result of bind success the user space open/configures the
   interfaces tough an IOCTL; the following stack trace has been
   identified on RZ/G3S:

Call trace:
dump_backtrace+0x9c/0x100
show_stack+0x20/0x38
dump_stack_lvl+0x48/0x60
dump_stack+0x18/0x28
ravb_open+0x70/0xa58
__dev_open+0xf4/0x1e8
__dev_change_flags+0x198/0x218
dev_change_flags+0x2c/0x80
devinet_ioctl+0x640/0x708
inet_ioctl+0x1e4/0x200
sock_do_ioctl+0x50/0x108
sock_ioctl+0x240/0x358
__arm64_sys_ioctl+0xb0/0x100
invoke_syscall+0x50/0x128
el0_svc_common.constprop.0+0xc8/0xf0
do_el0_svc+0x24/0x38
el0_svc+0x34/0xb8
el0t_64_sync_handler+0xc0/0xc8
el0t_64_sync+0x190/0x198

2/ this call may execute concurrently with ravb_remove() as the
   unbind/bind operation was executed in a loop
3/ if the operation mode is changed to RESET (through
   ravb_write(ndev, CCC_OPC_RESET, CCC) call in ravb_remove())
   while the above ravb_open() is in progress it may lead to MAC
   (or PHY, or MAC-PHY connection, the right point hasn't been identified
   at the moment) to be broken, thus the Ethernet connectivity fails to
   restore.

The simple fix for this is to move ravb_write(ndev, CCC_OPC_RESET, CCC))
after unregister_netdev() to avoid resetting the controller while the
netdev interface is still registered.

To avoid future issues in ravb_remove(), the patch follows the proper order
of operations in ravb_remove(): reverse order compared with ravb_probe().
This avoids described races as the IOCTLs as well as unregister_netdev()
(called now at the beginning of ravb_remove()) calls rtnl_lock() before
continuing and IOCTLs check (though devinet_ioctl()) if device is still
registered just after taking the lock:

int devinet_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr)
{
	// ...

        rtnl_lock();

        ret = -ENODEV;
        dev = __dev_get_by_name(net, ifr->ifr_name);
        if (!dev)
                goto done;

	// ...
done:
        rtnl_unlock();
out:
        return ret;
}

Fixes: c156633f ("Renesas Ethernet AVB driver proper")
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>