netdev - Re: [Intel-wired-lan] [PATCH net v2] i40e: fix endless loop under rtnl

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Date:   Wed, 15 Sep 2021 12:16:40 -0700
From:   Jesse Brandeburg <jesse.brandeburg@...il.com>
To:     Jiri Benc <jbenc@...hat.com>
Cc:     NetDEV list <netdev@...r.kernel.org>,
        intel-wired-lan@...ts.osuosl.org
Subject: Re: [Intel-wired-lan] [PATCH net v2] i40e: fix endless loop under rtnl

On Tue, Sep 14, 2021 at 1:55 AM Jiri Benc <jbenc@...hat.com> wrote:
>
> The loop in i40e_get_capabilities can never end. The problem is that
> although i40e_aq_discover_capabilities returns with an error if there's
> a firmware problem, the returned error is not checked. There is a check for
> pf->hw.aq.asq_last_status but that value is set to I40E_AQ_RC_OK on most
> firmware problems.
>
> When i40e_aq_discover_capabilities encounters a firmware problem, it will
> enocunter the same problem on its next invocation. As the result, the loop
> becomes endless. We hit this with I40E_ERR_ADMIN_QUEUE_TIMEOUT but looking
> at the code, it can happen with a range of other firmware errors.
>
> I don't know what the correct behavior should be: whether the firmware
> should be retried a few times, or whether pf->hw.aq.asq_last_status should
> be always set to the encountered firmware error (but then it would be
> pointless and can be just replaced by the i40e_aq_discover_capabilities
> return value). However, the current behavior with an endless loop under the
> rtnl mutex(!) is unacceptable and Intel has not submitted a fix, although we
> explained the bug to them 7 months ago.
>
> This may not be the best possible fix but it's better than hanging the whole
> system on a firmware bug.
>
> Fixes: 56a62fc86895 ("i40e: init code and hardware support")
> Tested-by: Stefan Assmann <sassmann@...hat.com>
> Signed-off-by: Jiri Benc <jbenc@...hat.com>


Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>

Thanks!