linux-kernel - Re: [PATCH net-next 0/7] rcu: prevent RCU_LOCKDEP

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Date:   Wed, 16 Sep 2020 17:48:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     davem@...emloft.net, joel@...lfernandes.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        rcu@...r.kernel.org, josh@...htriplett.org, peterz@...radead.org,
        christian.brauner@...ntu.com
Subject: Re: [PATCH net-next 0/7] rcu: prevent RCU_LOCKDEP_WARN() from
 swallowing  the condition

On Wed, 16 Sep 2020 16:15:05 -0700 Paul E. McKenney wrote:
> On Wed, Sep 16, 2020 at 11:45:21AM -0700, Jakub Kicinski wrote:
> > Hi!
> > 
> > So I unfolded the RFC patch into smaller chunks and fixed an issue
> > in SRCU pointed out by build bot. Build bot has been quiet for
> > a day but I'm not 100% sure it's scanning my tree, so let's
> > give these patches some ML exposure.
> > 
> > The motivation here is that we run into a unused variable
> > warning in networking code because RCU_LOCKDEP_WARN() makes
> > its argument disappear with !LOCKDEP / !PROVE_RCU. We marked
> > the variable as __maybe_unused, but that's ugly IMHO.
> > 
> > This set makes the relevant function declarations visible to
> > the compiler and uses (0 && (condition)) to make the compiler
> > remove those calls before linker realizes they are never defined.
> > 
> > I'm tentatively marking these for net-next, but if anyone (Paul?)
> > wants to take them into their tree - even better.  
> 
> I have pulled these into -rcu for review and further testing, thank you!
> I of course could not resist editing the commit logs, so please check
> to make sure that I did not mess anything up.

Done & thank you!

> Just so you know, unless this is urgent, it is in my v5.11 pile, that
> is, for the merge window after next.
> 
> If someone else wants to take them, please feel free to add my
> Acked-by to the RCU pieces.

Sounds good to me, the RCU tree seems most appropriate and we added 
a workaround for the issue in net-next already, anyway.

Thanks!