From: Jarek Poplawski <jarkao2@gmail.com>
This backtrace call path is anything but "usual".
There is a UDP send, and a local_bh_enable() done there triggers
softirqs, which processes device (I would guess loopback, or
some non-NAPI device) backlog processing.
This triggers an input netfilter ipt_LOG rule, which triggers a
printk over netconsole.
netpoll finds the TX queue of the tg3 device (which is NAPI)
full, so it invokes ->poll() to try and free up some TX queue
space.
This in turn triggers a packet receive, which hits bridging netfilter,
which does a conntrack lookup, which does the BH disable/enable which
triggers the warning.
I mean, this is just a very crazy trace :-)
I see an easy way around this. We should just punt on non-netpoll
RX packets that try to get processed during a netconsole ->poll()
run.
Wait a second, this is _supposed_ to be already happening. Perhaps
the tests in netpoll_rx() are screwed up.
net/core/netpoll.c'd poll_one_napi() explicitly sets NETPOLL_RX_DROP
in npinfo->rx_flags as well as increment "trapped", and that is
supposed to make netpoll_rx() return non-zero which tells the caller
to ignore and drop all RX packets.
What isn't that happening?
netpoll_rx()'s test is:
if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
return 0;
which looks perfectly fine. npinfo will be non-NULL by definition
because we are doing netpoll for netconsole on this device, and
->rx_flags are non-zero by the above mentioned code.
So we get to __netpoll_rx() by the next bit of code.
if (npinfo->rx_flags && __netpoll_rx(skb))
ret = 1;
And __netpoll_rx() says:
struct netpoll *np = npi->rx_np;
if (!np)
goto out;
this should trigger because a netpoll RX agent shouldn't be attached,
then:
out:
if (atomic_read(&trapped)) {
kfree_skb(skb);
return 1;
}
return 0;
which should trigger because trapped is non-zero, thus we free the SKB
and return 1.
We need to figure out why this isn't working ...
