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

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

On 8/16/21 9:15 AM, Jakub Kicinski wrote:

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On Fri, 13 Aug 2021 21:25:23 -0500 Alex Elder wrote:

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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