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Date: Sun, 26 Jul 2020 21:49:51 +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: Rakesh Pillai <pillair@...eaurora.org> > Sent: Friday, July 24, 2020 11:51 AM > To: 'Johannes Berg' <johannes@...solutions.net>; > 'ath10k@...ts.infradead.org' <ath10k@...ts.infradead.org> > Cc: 'linux-wireless@...r.kernel.org' <linux-wireless@...r.kernel.org>; > 'linux-kernel@...r.kernel.org' <linux-kernel@...r.kernel.org>; > 'kvalo@...eaurora.org' <kvalo@...eaurora.org>; 'davem@...emloft.net' > <davem@...emloft.net>; 'kuba@...nel.org' <kuba@...nel.org>; > 'netdev@...r.kernel.org' <netdev@...r.kernel.org>; > 'dianders@...omium.org' <dianders@...omium.org>; > 'evgreen@...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: Friday, July 24, 2020 1:37 AM > > 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 Thu, 2020-07-23 at 23:56 +0530, Rakesh Pillai wrote: > > > > > > > - 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. > > > > 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. > > > > 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. > Hi Johannes, We do have the usage of napi_gro_receive and netif_receive_skb in mac80211. /* deliver to local stack */ if (rx->napi) napi_gro_receive(rx->napi, skb); else netif_receive_skb(skb); Also all the rx_handlers are called under the " rx->local->rx_path_lock" lock. Is the BH disable still required ? > > > > johannes
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