linux-kernel - Re: [RFC PATCH 2/2] net: mac808211: mac802154: use lockdep_assert_in

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Date:   Fri, 4 May 2018 21:07:35 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        Ingo Molnar <mingo@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@....samsung.com>,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        linux-wpan@...r.kernel.org,
        Anna-Maria Gleixner <anna-maria@...utronix.de>
Subject: Re: [RFC PATCH 2/2] net: mac808211: mac802154: use
 lockdep_assert_in_softirq() instead own warning

On 2018-05-04 20:51:32 [+0200], Peter Zijlstra wrote:
> On Fri, May 04, 2018 at 08:45:39PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2018-05-04 20:32:49 [+0200], Peter Zijlstra wrote:
> > > On Fri, May 04, 2018 at 07:51:44PM +0200, Sebastian Andrzej Siewior wrote:
> > > > From: Anna-Maria Gleixner <anna-maria@...utronix.de>
> > > > 
> > > > The warning in ieee802154_rx() and ieee80211_rx_napi() is there to ensure
> > > > the softirq context for the subsequent netif_receive_skb() call. 
> > > 
> > > That's not in fact what it does though; so while that might indeed be
> > > the intent that's not what it does.
> > 
> > It was introduced in commit d20ef63d3246 ("mac80211: document
> > ieee80211_rx() context requirement"):
> > 
> >     mac80211: document ieee80211_rx() context requirement
> >     
> >     ieee80211_rx() must be called with softirqs disabled
> 
> softirqs disabled, ack that is exactly what it checks.
> 
> But afaict the assertion you introduced tests that we are _in_ softirq
> context, which is not the same.

indeed, now it clicked. Given what I wrote in the cover letter would you
be in favour of (a proper) lockdep_assert_BH_disabled() or the cheaper
local_bh_enable() (assuming the network folks don't mind the cheaper
version)?

Sebastian