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From:   "Rakesh Pillai" <pillair@codeaurora.org>
To:     "'Johannes Berg'" <johannes@sipsolutions.net>,
        <ath10k@lists.infradead.org>
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        <evgreen@chromium.org>
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Subject: RE: [RFC 1/7] mac80211: Add check for napi handle before WARN_ON
Date:   Fri, 24 Jul 2020 11:51:12 +0530
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> -----Original Message-----
> From: Johannes Berg <johannes@sipsolutions.net>
> Sent: Friday, July 24, 2020 1:37 AM
> To: Rakesh Pillai <pillair@codeaurora.org>; ath10k@lists.infradead.org
> Cc: linux-wireless@vger.kernel.org; linux-kernel@vger.kernel.org;
> kvalo@codeaurora.org; davem@davemloft.net; kuba@kernel.org;
> netdev@vger.kernel.org; dianders@chromium.org; evgreen@chromium.org
> Subject: Re: [RFC 1/7] mac80211: Add check for napi handle before
> WARN_ON
>=20
> On Thu, 2020-07-23 at 23:56 +0530, Rakesh Pillai wrote:
>=20
> > > > -	WARN_ON_ONCE(softirq_count() =3D=3D 0);
> > > > +	WARN_ON_ONCE(napi && softirq_count() =3D=3D 0);
> > >
> > > FWIW, I'm pretty sure this is incorrect - we make assumptions on
> > > softirqs being disabled in mac80211 for serialization and in place =
of
> > > some locking, I believe.
> > >
> >
> > I checked this, but let me double confirm.
> > But after this change, no packet is submitted from driver in a =
softirq
> context.
> > So ideally this should take care of serialization.
>=20
> I'd guess that we have some reliance on BHs already being disabled, =
for
> things like u64 sync updates, or whatnot. I mean, we did "rx_ni()" for =
a
> reason ... Maybe lockdep can help catch some of the issues.
>=20
> But couldn't you be in a thread and have BHs disabled too?

This would ideally beat the purpose and possibly hurt the other =
subsystems running on the same core.

>=20
> johannes