Re: [PATCH net-next 4/6] net: ipa: ensure hardware has power in ipa_start_xmit()

[Alex Elder]

On 8/16/21 9:20 AM, Alex Elder wrote:
> 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.

I'm finding this isn't an easy problem to solve (or even think
about).  While I ponder the best course of action I'm going
to send out another series (i.e., *before* I send a fix for
this issue) because I'd like to get everything I have out
for review this week.  I *will* address this potential race
one way or another, possibly later today.

					-Alex

>                      -Alex