netdev - Re: [RFC net-next 1/3] net: provide macros for commonly copied lockless queue stop/wake code

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Message-ID: <20230312184515.5eabc8df@hermes.local>
Date:   Sun, 12 Mar 2023 18:45:15 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        alexanderduyck@...com, roman.gushchin@...ux.dev
Subject: Re: [RFC net-next 1/3] net: provide macros for commonly copied
 lockless queue stop/wake code

On Sun, 12 Mar 2023 21:37:39 -0400
Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:

> Stephen Hemminger wrote:
> > On Fri, 10 Mar 2023 21:01:28 -0800
> > Jakub Kicinski <kuba@...nel.org> wrote:
> >   
> > > A lot of drivers follow the same scheme to stop / start queues
> > > without introducing locks between xmit and NAPI tx completions.
> > > I'm guessing they all copy'n'paste each other's code.
> > > 
> > > Smaller drivers shy away from the scheme and introduce a lock
> > > which may cause deadlocks in netpoll.
> > > 
> > > Provide macros which encapsulate the necessary logic.  
> > 
> > Could any of these be inline functions instead for type safety?  
> 
> I suppose not because of the condition that is evaluated.

It is more that the condition needs to evaluated after some other
pre-conditions.