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

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Message-ID: <20200914173029.60bdfc02@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 14 Sep 2020 17:30:29 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Paul E. McKenney" <paulmck@...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, 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!