netdev - Re: [PATCH net 2/2] net/mlx4_core: mlx4_init_slave() shouldn't access comm channel before PF is ready

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Message-ID: <CAJZOPZKfZ3Lp7XwasR19M1QC+5+ksQst8SORAxi2A7NVeHp7qg@mail.gmail.com>
Date:	Thu, 6 Mar 2014 23:58:19 +0200
From:	Or Gerlitz <or.gerlitz@...il.com>
To:	David Miller <davem@...emloft.net>, Don Dutile <ddutile@...hat.com>
Cc:	Amir Vadai <amirv@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.com>, Narendra_K@...l.com,
	Sreekanth_Reddy@...l.com,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net 2/2] net/mlx4_core: mlx4_init_slave() shouldn't access
 comm channel before PF is ready

On Thu, Mar 6, 2014 at 11:12 PM, David Miller <davem@...emloft.net> wrote:
> From: Or Gerlitz <or.gerlitz@...il.com>
> Date: Thu, 6 Mar 2014 23:08:36 +0200
>> On Thu, Mar 6, 2014 at 10:48 PM, David Miller <davem@...emloft.net> wrote:
>>> From: Or Gerlitz <or.gerlitz@...il.com>
>>> Date: Thu, 6 Mar 2014 22:19:48 +0200

>>>>> This synchronization scheme doesn't look right to me at all.
>>>>> It's global, so VF's for _any_ PF will probe defer while one is enabling SRIOV.
>>>>> It doesn't seem correct to cause unrelated VF's to defer the probe.
>>>> Can you please elaborate a bit why you find this approach to be
>>>> incorrect? basically, these nested VF probed are a bit headache
>>>> anyway, so we didn't find such global deferring to be problematic.

>>> What if a second PF starts to init and call pci_enable_sriov(), while the VFs
>>> from a previous PF probed call mlx4_init_slave()?
>>> It will increment pf_loading() and force those unreladed VFs to defer.

>> By "unreladed VFs" I assume you mean unrelated VFs that belong to the
>> 1st VF, which is OK for them to probe, right? so yes, this is sort of
>> conservative approach that wait till all PFs are fully ready, and I
>> understand you don't like it, but still, I would be happy to know
>> what's wrong in doing so..

> My understanding is that the relationship between these devices is:
>         PF --> VF1, VF2, VF3, ...
>
> and these VF children are (essentially) instantiated by
> pci_enable_sriov() calls.
>
> Therefore if we:
>
>         probe PF1
>
> we go:
>
>         pf_loading++
>         pci_enable_sriov();
>         PF1_VF1 defers
>         PF1_VF2 defers
>         PF1_VF3 defers
>         ...
>         pf_loading--
>
> next:
>
>         probe PF2
>
>         pf_loading++
> ..

correct, that would be the situation

> at this point any attempt of PF1's VFs to init will defer, what will
> cause them to properly retry that init?

So... we were thinking that there is a mechanism that causes them to
retry that init as long as they return -EPROBE_DEFER or they succeed,
isn't that the case?
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