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Date:   Fri, 21 Jul 2023 15:34:27 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Joe Perches <joe@perches.com>
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com, rostedt@goodmis.org,
        Andy Whitcroft <apw@canonical.com>,
        Dwaipayan Ray <dwaipayanray1@gmail.com>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>, bpf@vger.kernel.org
Subject: Re: [PATCH rcu 5/5] checkpatch: Complain about unexpected uses of
 RCU Tasks Trace
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On Thu, Jul 20, 2023 at 09:38:51PM -0700, Joe Perches wrote:
> On Thu, 2023-07-20 at 20:56 -0700, Paul E. McKenney wrote:
> 
> > 
> > > That works much better, thank you!  I will update the patch on my
> > > next rebase.
> > 
> > As shown below.  Is this what you had in mind?
> []
> > commit 496aa3821b40459b107f4bbc14ca867daad21fb6
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date:   Thu Jul 6 11:48:07 2023 -0700
> > 
> >     checkpatch: Complain about unexpected uses of RCU Tasks Trace
> >     
> >     RCU Tasks Trace is quite specialized, having been created specifically
> >     for sleepable BPF programs.  Because it allows general blocking within
> >     readers, any new use of RCU Tasks Trace must take current use cases into
> >     account.  Therefore, update checkpatch.pl to complain about use of any of
> >     the RCU Tasks Trace API members outside of BPF and outside of RCU itself.
> []
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> []
> > @@ -7457,6 +7457,30 @@ sub process {
> >  			}
> >  		}
> >  
> > +# Complain about RCU Tasks Trace used outside of BPF (and of course, RCU).
> > +		our $rcu_trace_funcs = qr{(?x:
> > +			rcu_read_lock_trace |
> > +			rcu_read_lock_trace_held |
> > +			rcu_read_unlock_trace |
> > +			call_rcu_tasks_trace |
> > +			synchronize_rcu_tasks_trace |
> > +			rcu_barrier_tasks_trace |
> > +			rcu_request_urgent_qs_task
> > +		)};
> > +		our $rcu_trace_paths = qr{(?x:
> > +			kernel/bpf/ |
> > +			include/linux/bpf |
> > +			net/bpf/ |
> > +			kernel/rcu/ |
> > +			include/linux/rcu
> > +		)};
> > +		if ($line =~ /\b$rcu_trace_funcs\s*\(/) {
> > +			if ($realfile !~ m@^$rcu_trace_paths@) {
> > +				WARN("RCU_TASKS_TRACE",
> > +				     "use of RCU tasks trace is incorrect outside BPF or core RCU code\n" . $herecurr);
> 
> Exactly yes.
> 
> (though I still suggest a capture group to show the function like below)
> 
> 		if ($line =~ /\b($rcu_trace_funcs)\s*\(/ &&
> 		    $realfile !~ m{^$rcu_trace_paths}) {
> 			WARN("RCU_TASKS_TRACE",
> 			     "use of RCU task trace '$1' is incorrect outside BPF or core RCU code\n" . $herecurr);
> 		}

That does seem to work!

I will fold this change in on my next rebase.

							Thanx, Paul