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

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Message-ID: <20210816071543.39a44815@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 16 Aug 2021 07:15:43 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alex Elder <elder@...aro.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 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.