Re: [PATCH 4/8] iwlwifi: mvm: fix race in sync rx queue notification

[Luca Coelho <luca@coelho.fi>]

On Fri, 2019-10-04 at 16:41 +0300, Kalle Valo wrote:
> Luca Coelho <luca@coelho.fi> writes:
> 
> > From: Naftali Goldstein <naftali.goldstein@intel.com>
> > 
> > Consider the following flow:
> >  1. Driver starts to sync the rx queues due to a delba.
> >     mvm->queue_sync_cookie=1.
> >     This rx-queues-sync is synchronous, so it doesn't increment the
> >     cookie until all rx queues handle the notification from FW.
> >  2. During this time, driver starts to sync rx queues due to nssn sync
> >     required.
> >     The cookie's value is still 1, but it doesn't matter since this
> >     rx-queue-sync is non-synchronous so in the notification handler the
> >     cookie is ignored.
> >     What _does_ matter is that this flow increments the cookie to 2
> >     immediately.
> >     Remember though that the FW won't start servicing this command until
> >     it's done with the previous one.
> >  3. FW is still handling the first command, so it sends a notification
> >     with internal_notif->sync=1, and internal_notif->cookie=0, which
> >     triggers a WARN_ONCE.
> > 
> > The solution for this race is to only use the mvm->queue_sync_cookie in
> > case of a synchronous sync-rx-queues. This way in step 2 the cookie's
> > value won't change so we avoid the WARN.
> > 
> > The commit in the "fixes" field is the first commit to introduce
> > non-synchronous sending of this command to FW.
> 
> But I don't see a Fixes field anywhere :)

Hmmm, good catch.  My script should have added it.  One more thing to
check... *sigh*

This is the aforementioned commit:

Fixes: 3c514bf831ac ("iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues")

I'll add it and include it when I send the pull-req.

Thanks!

--
Cheers,
Luca.