linux-kernel - RE: [RFC 1/7] mac80211: Add check for napi handle before WARN

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Date:   Thu, 23 Jul 2020 23:56:18 +0530
From:   "Rakesh Pillai" <pillair@...eaurora.org>
To:     "'Johannes Berg'" <johannes@...solutions.net>,
        <ath10k@...ts.infradead.org>
Cc:     <linux-wireless@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kvalo@...eaurora.org>, <davem@...emloft.net>, <kuba@...nel.org>,
        <netdev@...r.kernel.org>, <dianders@...omium.org>,
        <evgreen@...omium.org>
Subject: RE: [RFC 1/7] mac80211: Add check for napi handle before WARN_ON



> -----Original Message-----
> From: Johannes Berg <johannes@...solutions.net>
> Sent: Wednesday, July 22, 2020 6:26 PM
> To: Rakesh Pillai <pillair@...eaurora.org>; ath10k@...ts.infradead.org
> Cc: linux-wireless@...r.kernel.org; linux-kernel@...r.kernel.org;
> kvalo@...eaurora.org; davem@...emloft.net; kuba@...nel.org;
> netdev@...r.kernel.org; dianders@...omium.org; evgreen@...omium.org
> Subject: Re: [RFC 1/7] mac80211: Add check for napi handle before
> WARN_ON
> 
> On Tue, 2020-07-21 at 22:44 +0530, Rakesh Pillai wrote:
> > The function ieee80211_rx_napi can be now called
> > from a thread context as well, with napi context
> > being NULL.
> >
> > Hence add the napi context check before giving out
> > a warning for softirq count being 0.
> >
> > Tested-on: WCN3990 hw1.0 SNOC WLAN.HL.3.1-01040-QCAHLSWMTPLZ-1
> >
> > Signed-off-by: Rakesh Pillai <pillair@...eaurora.org>
> > ---
> >  net/mac80211/rx.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
> > index a88ab6f..1e703f1 100644
> > --- a/net/mac80211/rx.c
> > +++ b/net/mac80211/rx.c
> > @@ -4652,7 +4652,7 @@ void ieee80211_rx_napi(struct ieee80211_hw
> *hw, struct ieee80211_sta *pubsta,
> >  	struct ieee80211_supported_band *sband;
> >  	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
> >
> > -	WARN_ON_ONCE(softirq_count() == 0);
> > +	WARN_ON_ONCE(napi && softirq_count() == 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.


> johannes