Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"

From: Brian Starkey
Date: Wed Nov 16 2016 - 16:01:52 EST

On Wed, Nov 16, 2016 at 10:49:06AM -0800, Eric Dumazet wrote:
On Wed, Nov 16, 2016 at 10:01 AM, Brian Starkey <brian.starkey@xxxxxxx> wrote:

The smc91x driver does seem to have some trickiness around softirqs.
I'm not familiar with net drivers, but I'll see if I can figure
anything out there.

Oh this code looks ugly :(

Do you have CONFIG_SMP=y or not ?

Yeah CONFIG_SMP=y (and CONFIG_PREEMPT=y too, fwiw).

I did try forcing it into the no-op locking (as though config SMP
wasn't set), it didn't help (and it doesn't look like that would be
safe with CONFIG_PREEMPT=y either).

The bit in smc_hardware_send_pkt looks like skipping softirq
invocation when there's already one running wouldn't give the same
behaviour as before:

if (!smc_special_trylock(&lp->lock, flags)) {

... that said, I've no idea if that matters.

Of course I also don't know if the network driver is even to blame :-(