linux-kernel - Re: [PATCH rcu 5/5] checkpatch: Complain about unexpected uses of RCU Tasks Trace

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Date:   Mon, 17 Jul 2023 15:34:14 -0700
From:   Joe Perches <joe@...ches.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org, Andy Whitcroft <apw@...onical.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org
Subject: Re: [PATCH rcu 5/5] checkpatch: Complain about unexpected uses of
 RCU Tasks Trace

On Mon, 2023-07-17 at 11:04 -0700, Paul E. McKenney wrote:
> 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.
> 
> Cc: Andy Whitcroft <apw@...onical.com> (maintainer:CHECKPATCH)
> Cc: Joe Perches <joe@...ches.com> (maintainer:CHECKPATCH)
> Cc: Dwaipayan Ray <dwaipayanray1@...il.com> (reviewer:CHECKPATCH)
> Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: <bpf@...r.kernel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  scripts/checkpatch.pl | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -7457,6 +7457,24 @@ sub process {
>  			}
>  		}
>  
> +# Complain about RCU Tasks Trace used outside of BPF (and of course, RCU).
> +		if ($line =~ /\brcu_read_lock_trace\s*\(/ ||
> +		    $line =~ /\brcu_read_lock_trace_held\s*\(/ ||
> +		    $line =~ /\brcu_read_unlock_trace\s*\(/ ||
> +		    $line =~ /\bcall_rcu_tasks_trace\s*\(/ ||
> +		    $line =~ /\bsynchronize_rcu_tasks_trace\s*\(/ ||
> +		    $line =~ /\brcu_barrier_tasks_trace\s*\(/ ||
> +		    $line =~ /\brcu_request_urgent_qs_task\s*\(/) {
> +			if ($realfile !~ m@...rnel/bpf@ &&
> +			    $realfile !~ m@...clude/linux/bpf@ &&
> +			    $realfile !~ m@...t/bpf@ &&
> +			    $realfile !~ m@...rnel/rcu@ &&
> +			    $realfile !~ m@...clude/linux/rcu@) {

Functions and paths like these tend to be accreted.

Please use a variable or 2 like:

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/bfp/ |
	include/linux/bpf |
	net/bpf/ |
	kernel/rcu/ |
	include/linux/rcu
)};

...
	
		if ($line =~ /\b($rcu_trace_funcs)\s*\(/ &&
		    $realfile !~ m{^$rcu_trace_paths}) {
			WARN("RCU_TASKS_TRACE",
			     "use of RCU tasks trace '$1' is incorrect outside BPF or core RCU code\n" . $herecurr);			}
		}