netdev - Re: [PATCH net-next 4/6] net: ipa: ensure hardware has power in ipa_start

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Date:   Mon, 16 Aug 2021 09:20:40 -0500
From:   Alex Elder <elder@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, bjorn.andersson@...aro.org,
        evgreen@...omium.org, cpratapa@...eaurora.org,
        subashab@...eaurora.org, elder@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 4/6] net: ipa: ensure hardware has power in
 ipa_start_xmit()

On 8/16/21 9:15 AM, Jakub Kicinski wrote:
> On Fri, 13 Aug 2021 21:25:23 -0500 Alex Elder wrote:
>>> This is racy, what if the pm work gets scheduled on another CPU and
>>> calls wake right here (i.e. before you call netif_stop_queue())?
>>> The queue may never get woken up?
>>
>> I haven't been seeing this happen but I think you may be right.
>>
>> I did think about this race, but I think I was relying on the
>> PM work queue to somehow avoid the problem.  I need to think
>> about this again after a good night's sleep.  I might need
>> to add an atomic flag or something.
> 
> Maybe add a spin lock?  Seems like the whole wake up path will be
> expensive enough for a spin lock to be in the noise. You can always
> add complexity later.

Exactly what I just decided after trying to work out a
clever way without using a spinlock...  I'll be sending
out a fix today.  Thanks.

					-Alex