Re: netconsole hangs w/ alt-sysrq-t

[Jeff Moyer <jmoyer@redhat.com>]

==> Regarding Re: netconsole hangs w/ alt-sysrq-t; Matt Mackall <mpm@selenic.com> adds:

mpm> On Wed, Apr 28, 2004 at 08:44:47AM -0400, Jeff Moyer wrote:
>> ==> Regarding Re: netconsole hangs w/ alt-sysrq-t; Matt Mackall
>> <mpm@selenic.com> adds:
>> 
mpm> On Thu, Apr 22, 2004 at 11:29:33AM -0400, Jeff Moyer wrote:
>> >> If netconsole is enabled, and you hit Alt-Sysrq-t, then it will print
>> a >> small amount of output to the console(s) and then hang the system.
>> In >> this case, I'm using the e100 driver, and we end up exhausting the
>> >> available cbs.  Since we are in interrupt context, the driver's poll
>> >> routine is never run, and we loop infinitely waiting for resources to
>> >> free up that never will.  Kernel version is 2.6.5.
>> 
mpm> Can you try 2.6.6-rc2? It has a fix to congestion handling that should
mpm> address this.
>> Is the attached patch the change you are referring to?  If so, I don't
>> see how this would fix the problem.  I ended up deferring netpoll writes
>> to process context, which has been working fine for me.  Have I missed
>> something?

mpm> Well process context defeats the purpose. Ok, I've more closely read
mpm> your report and if I understand correctly, you're using the NAPI
mpm> version of e100? There's some magic NAPI bits in netpoll_poll that
mpm> might help here:

Yes, sorry I didn't specify that earlier.

mpm>         if(trapped && np->dev->poll && test_bit(__LINK_STATE_RX_SCHED,
mpm> &np->dev->state))
np-> dev->poll(np->dev, &budget);

mpm> Perhaps we need to pull the trapped test out of there. Then with any
mpm> luck, dev->hard_start_xmit will return non-zero in netpoll_send_skb,
mpm> we'll call netpoll_poll to pump the card, and we'll be able to flush
mpm> it.

I don't think so.  You can end up in code running in interrupt context that
is not designed to (ip routing code, etc).  I've been down that path
already.  I only defer to process context if irqs_disabled().

Other suggestions?

-Jeff