Re: infinite spin in RT when booting with DHCP on

["Tim Sander" <tim.sander@hbm.com>]

Hi
> When booting my platform with DHCP on, the DHCP request is sent by the
> network driver before the PHY has even started the autonegotiation.
> Since the PHY is not ready, the TX interrupt returns with NETDEV_TX_BUSY
> but the softirq [sirq-net-tx] seems to have entered an infinite spin, as
> my system is practically hung and 'top' reveals [sirq-net-tx/0] is
> consuming 95% of CPU. This is preventing the PHY autonegotiation (which is
> scheduled as a delayed work) to start, so the PHY is never ready and the
> packet never reaches the network.
Mh, i think i am hit by the same problem. I have a i.mx 35 and when dhcp is
enabled the ksoftirq is also running wild with 3.0-rt. This also happens when
static ip is configured and the probably during network transfer the network
interface is reconfigured. Basically it seems the sirq-net-tx thread tries to
send a packet on a non configured interface.

But one thing that makes me thinking, is that this thing is only happening on
arm and not on x86. So Hector what platform are you working on. Are you by
chance using the same fec.c ethernet driver?

I have verified that in my case the driver takes always the return statement in
line fec.c:247: return NETXDEV_TX_BUSY;  
It never stops on a breakpoint set on line 250 which shows that the interface
gets never configured.

I have taken some screenshots of my hw debugger:

trace:http://private.vlsi.informatik.tu-darmstadt.de/tstone/linux/fec_enet_start_xmit.png
stack:http://private.vlsi.informatik.tu-darmstadt.de/tstone/linux/fec_enet_start_xmit_stacktrace.png
locals:http://private.vlsi.informatik.tu-darmstadt.de/tstone/linux/fec_enet_start_xmit_stack+locals.png

Whats interesting to note is that phy_dev and mii_dev are both null pointers.

Best regards
Tim

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