Re: [net] protecting interfaces from races between control and data ?

What do you think about this change?

Cheers,

Jack



On Mon, Aug 5, 2013 at 10:58 AM, Luigi Rizzo <rizzo_at_iet.unipi.it> wrote:

> On Mon, Aug 5, 2013 at 7:49 PM, Jack Vogel <jfvogel_at_gmail.com> wrote:
>
>> Sigh, this ends up being ugly I'm afraid. I need some time to look at
>> code and think about it.
>>
>>
> actually the intel drivers seem in decent shape,
> especially if we reuse IFF_DRV_RUNNING as the reset flag
> and the core+queue lock in the control path.
>
> cheers
> luigi
>
>
>
>> Jack
>>
>>
>>
>> On Mon, Aug 5, 2013 at 10:36 AM, Luigi Rizzo <rizzo_at_iet.unipi.it> wrote:
>>
>>> On Mon, Aug 5, 2013 at 7:17 PM, Adrian Chadd <adrian_at_freebsd.org> wrote:
>>>
>>> > I'm travelling back to San Jose today; poke me tomorrow and I'll brain
>>> > dump what I did in ath(4) and the lessons learnt.
>>> >
>>> > The TL;DR version - you don't want to grab an extra lock in the
>>> > read/write paths as that slows things down. Reuse the same per-queue
>>> > TX/RX lock and have:
>>> >
>>> > * a reset flag that is set when something is resetting; that says to
>>> > the queue "don't bother processing anything, just dive out";
>>> > * 'i am doing Tx / Rx' flags per queue that is set at the start of
>>> > TX/RX servicing and finishes at the end; that way the reset code knows
>>> > if there's something pending;
>>> > * have the reset path grab each lock, set the 'reset' flag on each,
>>> > then walk each queue again and make sure they're all marked as 'not
>>> > doing TX/RX'. At that point the reset can occur, then the flag cna be
>>> > cleared, then TX/RX can resume.
>>> >
>>>
>>> so this is slightly different from what Bryan suggested (and you
>>> endorsed)
>>> before, as in that case there was a single 'reset' flag IFF_DRV_RUNNING
>>> protected by the 'core' lock, then a nested round on all tx and rx locks
>>> to make sure that all customers have seen it.
>>> In both cases the tx and rx paths only need the per-queue lock.
>>>
>>> As i see it, having a per-queue reset flag removes the need for nesting
>>> core + queue locks, but since this is only in the control path perhaps
>>> it is not a big deal (and is better to have a single place to look at to
>>> tell whether or not we should bail out).
>>>
>>> cheers
>>> luigi
>>>
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>>
>>
>
>
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> -----------------------------------------+-------------------------------
>  Prof. Luigi RIZZO, rizzo_at_iet.unipi.it  . Dip. di Ing. dell'Informazione
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