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SubjectRe: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"
Hi Eric,

On Thu, Nov 17, 2016 at 07:29:14AM -0800, Eric Dumazet wrote:
>On Wed, Nov 16, 2016 at 1:01 PM, Brian Starkey <brian.starkey@arm.com> wrote:
>> 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@arm.com>
>>> 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)) {
>> netif_stop_queue(dev);
>> tasklet_schedule(&lp->tx_task);
>> return;
>> }
>>
>> ... that said, I've no idea if that matters.
>>
>> Of course I also don't know if the network driver is even to blame :-(
>>
>
>I believe the problem is in SMC_WAIT_MMU_BUSY()
>
>Could you try this patch ? (inlined and attached)
>

No joy with this patch :-(

I had to add an ioaddr argument because apparently that macro depends
on local context (yuck...), but it doesn't help my issue.

FWIW I don't see any timeouts, either with or without the patch.
(I don't know for sure, but I would guess that the model of the
network card doesn't model whatever stall that loop is checking for.
It probably just completes all MMU operations immediately)

-Brian

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