netdev - Re: [PATCH net-next] rcu: prevent RCU_LOCKDEP_WARN() from swallowing the condition

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Message-ID: <20200915170218.GN29330@paulmck-ThinkPad-P72>
Date:   Tue, 15 Sep 2020 10:02:18 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        nikolay@...ulusnetworks.com, davem@...emloft.net,
        netdev@...r.kernel.org, josh@...htriplett.org,
        peterz@...radead.org, christian.brauner@...ntu.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        sfr@...b.auug.org.au, roopa@...dia.com
Subject: Re: [PATCH net-next] rcu: prevent RCU_LOCKDEP_WARN() from swallowing
 the condition

On Mon, Sep 14, 2020 at 05:30:29PM -0700, Jakub Kicinski wrote:
> On Mon, 14 Sep 2020 17:20:11 -0700 Paul E. McKenney wrote:
> > > Seems like quite a few places depend on the macro disappearing its
> > > argument. I was concerned that it's going to be had to pick out whether
> > > !LOCKDEP builds should return true or false from LOCKDEP helpers, but
> > > perhaps relying on the linker errors even more is not such poor taste?
> > > 
> > > Does the patch below look acceptable to you?  
> > 
> > The thing to check would be whether all compilers do sufficient
> > dead-code elimination (it used to be that they did not).  One way to
> > get a quick sniff test of this would be to make sure that a dead-code
> > lockdep_is_held() is in common code, and then expose this patch to kbuild
> > test robot.
> 
> I'm pretty sure it's in common code because kbuild bot complaints were
> the reason I gave up the first time around ;) 
> 
> I'll expose this to kbuild bot via my kernel.org tree in case it
> doesn't consider scissored patches and report back!

Sounds good, thank you!

							Thanx, Paul