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Date:   Thu, 20 Jul 2023 12:43:55 -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
Message-ID: <798959b0-b107-44c4-8262-075930ebfeaa@paulmck-laptop>
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On Thu, Jul 20, 2023 at 12:29:42AM -0700, Joe Perches wrote:
> On Mon, 2023-07-17 at 16:34 -0700, Paul E. McKenney wrote:
> > On Mon, Jul 17, 2023 at 03:34:14PM -0700, Joe Perches wrote:
> > > 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@canonical.com> (maintainer:CHECKPATCH)
> > > > Cc: Joe Perches <joe@perches.com> (maintainer:CHECKPATCH)
> > > > Cc: Dwaipayan Ray <dwaipayanray1@gmail.com> (reviewer:CHECKPATCH)
> > > > Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
> > > > Cc: Alexei Starovoitov <ast@kernel.org>
> > > > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > > > Cc: John Fastabend <john.fastabend@gmail.com>
> > > > Cc: <bpf@vger.kernel.org>
> > > > Signed-off-by: Paul E. McKenney <paulmck@kernel.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@^kernel/bpf@ &&
> > > > +			    $realfile !~ m@^include/linux/bpf@ &&
> > > > +			    $realfile !~ m@^net/bpf@ &&
> > > > +			    $realfile !~ m@^kernel/rcu@ &&
> > > > +			    $realfile !~ m@^include/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/ |
> 		^^
> 	kernel/bfp/ |
> 
> (umm, oops...)
> I think my original suggestion works better when I don't typo the path.

Color me blind!  ;-)

That works much better, thank you!  I will update the patch on my
next rebase.

							Thanx, Paul

> > > 	include/linux/bpf |
> > > 	net/bpf/ |
> > > 	kernel/rcu/ |
> > > 	include/linux/rcu
> > > )};
> > 
> > Like this?
> > 
> > # 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 $rcu_trace_paths = qr{(?x:
> > 			kernel/bfp/ |
> > 			include/linux/bpf |
> > 			net/bpf/ |
> > 			kernel/rcu/ |
> > 			include/linux/rcu
> > 		)};
> > 		if ($line =~ /$rcu_trace_funcs/) {
> > 			if ($realfile !~ m@^$rcu_trace_paths@) {
> > 				WARN("RCU_TASKS_TRACE",
> > 				     "use of RCU tasks trace is incorrect outside BPF or core RCU code\n" . $herecurr);
> > 			}
> > 		}
> > 
> > No, that is definitely wrong.  It has lost track of the list of pathnames,
> > thus complaining about uses of those functions in files where their use
> > is permitted.
> > 
> > But this seems to work:
> > 
> > # Complain about RCU Tasks Trace used outside of BPF (and of course, RCU).
> > 		our $rcu_trace_funcs = qr{(?x:
> > 			rcu_read_lock_trace |
> > 			rcu_read_lock_trace_held |
> > 			rcu_read_unlock_trace |
> > 			call_rcu_tasks_trace |
> > 			synchronize_rcu_tasks_trace |
> > 			rcu_barrier_tasks_trace |
> > 			rcu_request_urgent_qs_task
> > 		)};
> > 		if ($line =~ /\b$rcu_trace_funcs\s*\(/) {
> > 			if ($realfile !~ m@^kernel/bpf@ &&
> > 			    $realfile !~ m@^include/linux/bpf@ &&
> > 			    $realfile !~ m@^net/bpf@ &&
> > 			    $realfile !~ m@^kernel/rcu@ &&
> > 			    $realfile !~ m@^include/linux/rcu@) {
> > 				WARN("RCU_TASKS_TRACE",
> > 				     "use of RCU tasks trace is incorrect outside BPF or core RCU code\n" . $herecurr);
> > 			}
> > 		}
> > 
> > Maybe the "^" needs to be distributed into $rcu_trace_paths?
> > 
> > # 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 $rcu_trace_paths = qr{(?x:
> > 			^kernel/bfp/ |
> > 			^include/linux/bpf |
> > 			^net/bpf/ |
> > 			^kernel/rcu/ |
> > 			^include/linux/rcu
> > 		)};
> > 		if ($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);
> > 			}
> > 		}
> > 
> > But no joy here, either.  Which is no surprise, given that perl is
> > happy to distribute the "\b" and the "\s*\(" across the elements of
> > $rcu_trace_funcs.  I tried a number of other variations, including
> > inverting the "if" condition "(!(... =~ ...))", inverting the "if"
> > condition via an empty "then" clause, replacing the "m@" with "/",
> > replacing the "|" in the "qr{}" with "&", and a few others.
> > 
> > Again, listing the pathnames explicitly in the second "if" condition
> > works just fine.
> > 
> > Help?
> > 
> > 							Thanx, Paul
>