linux-kernel - Re: [PATCH 13/13] rcu/kvfree: Eliminate k[v]free

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Message-ID: <20230306151203.GC3280216@google.com>
Date:   Mon, 6 Mar 2023 15:12:03 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
        Jens Axboe <axboe@...nel.dk>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Bryan Tan <bryantan@...are.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Bob Pearson <rpearsonhpe@...il.com>,
        Ariel Levkovich <lariel@...dia.com>,
        Theodore Ts'o <tytso@....edu>, Julian Anastasov <ja@....bg>
Subject: Re: [PATCH 13/13] rcu/kvfree: Eliminate k[v]free_rcu() single
 argument macro

On Mon, Mar 06, 2023 at 07:01:08AM -0800, Paul E. McKenney wrote:
[..] 
> > > 7.	We then evaluate whether further cleanups are needed.
> > > 
> > > > > My feeling is
> > > > > that, we introduced "_mightsleep" macros first and after that try to
> > > > > convert users.
> > > 
> > > > One stopgap could be to add a checkpatch error if anyone tries to use old API,
> > > > and then in the meanwhile convert all users.
> > > > Though, that requires people listening to checkpatch complaints.
> > > 
> > > Every person who listens is that much less hassle.  It doesn't have to
> > > be perfect.  ;-)
> > 
> > The below checkpatch change can catch at least simple single-arg uses (i.e.
> > not having compound expressions inside of k[v]free_rcu() args). I will submit
> > a proper patch to it which we can include in this set.
> > 
> > Thoughts?
> > ---
> >  scripts/checkpatch.pl | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > index 78cc595b98ce..fc73786064b3 100755
> > --- a/scripts/checkpatch.pl
> > +++ b/scripts/checkpatch.pl
> > @@ -6362,6 +6362,15 @@ sub process {
> >  			}
> >  		}
> >  
> > +# check for soon-to-be-deprecated single-argument k[v]free_rcu() API
> > +		if ($line =~ /\bk[v]?free_rcu\s*\([^(]+\)/) {
> > +			if ($line =~ /\bk[v]?free_rcu\s*\([^,]+\)/) {
> > +				ERROR("DEPRECATED_API",
> > +				      "Single-argument k[v]free_rcu() API is deprecated, please pass an rcu_head object." . $herecurr);
> 
> Nice!
> 
> But could you please also tell them what to use instead?  Sure, they
> could look it up, but if it tells them directly, they are less likely
> to ignore it.

Sounds good, I will modify the warning to include the API to call and send
out a patch soon.

thanks,

 - Joel