Re: netpoll_setup questions

[Jeff Moyer <jmoyer@redhat.com>]

==> Regarding Re: netpoll_setup questions; Matt Mackall <mpm@selenic.com> adds:

mpm> On Wed, Oct 27, 2004 at 02:58:04PM -0400, Jeff Moyer wrote:
>> ==> Regarding Re: netpoll_setup questions; Matt Mackall
>> <mpm@selenic.com> adds:
>> 
mpm> On Wed, Oct 27, 2004 at 11:50:05AM -0400, Jeff Moyer wrote:
>> >> Hi, Matt,
>> >> 
>> >> The section of code in the body of this if statement:
>> >> 
>> >> if (!(ndev->flags & IFF_UP)) {
>> >> 
>> >> is a bit broken.  First, upon discussion with jgarzik, it seems we >>
>> should not check for IFF_UP, but instead do netif_running.
>> 
mpm> Well I cribbed it from the nfsroot code, which is perhaps not up on
mpm> fashion.
>> Hmm, I can't seem to find the relevant code.  Where is it?

mpm> net/ipv4/ipconfig.c, IIRC.
 
mpm> I don't expect it does. Usually we have our own IP address from the
mpm> command line, but if we don't, we will check if there's an in_dev
mpm> connected to the device and if so, look up the device's IP. This is
mpm> useful for the modular case where the network is up before we start
mpm> and we have a handy default for local IP.
>> Right, but the case in question is the one where we don't have a local
>> IP
specified>

mpm> Yeah..
 
>> if (!np->local_ip) {

mpm> "but if we don't"

>> rcu_read_lock(); in_dev = __in_dev_get(ndev);
>> 
>> if (!in_dev) {

mpm> "we will check if there's an in_dev"

>> rcu_read_unlock(); printk(KERN_ERR "%s: no IP address for %s,
>> aborting\n",
np-> name, np->dev_name);
>> goto release; }
>> 
np-> local_ip = ntohl(in_dev->ifa_list->ifa_local);

mpm> "if so, look up the device's IP"

>> rcu_read_unlock(); printk(KERN_INFO "%s: local IP %d.%d.%d.%d\n",
np-> name, HIPQUAD(np->local_ip));
>> }
>> 
>> 
>> >> And, in the case where it doesn't, you will get an oops further on
>> when >> dereferencing the ifa_list.
>> 
mpm> Does this actually happen? I'm checking in_dev for null already, but
mpm> perhaps I need to check ifa_list as well.
>> Yes, that should do it.

mpm> Again, does the oops actually happen? I'd expect I'd have seen it by
mpm> now if this were really a problem, but I don't mind adding another
mpm> check.

I'm sorry, I should have said this before.  Yes, it occurs.  You simply
need to have an interface in the down state, plugged into a network that
will not auto-assign an address.  Then, modprobe netconsole, and don't
specify what the local IP address is.  Believe it or not, I have a bug
filed on this.  ;)

-Jeff