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Date: Wed, 19 Jul 2023 11:27:52 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Joel Fernandes <joel@...lfernandes.org>
Cc: Joe Perches <joe@...ches.com>, rcu@...r.kernel.org,
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 Wed, Jul 19, 2023 at 07:51:58AM -0400, Joel Fernandes wrote:
>
>
> On 7/17/23 19:34, 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@...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
> > > )};
> >
> > 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@...cu_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@...rnel/bpf@ &&
> > $realfile !~ m@...clude/linux/bpf@ &&
> > $realfile !~ m@...t/bpf@ &&
> > $realfile !~ m@...rnel/rcu@ &&
> > $realfile !~ m@...clude/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@...u_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.
> >
>
> Not a perl expert but I wonder if the following are any options at all:
>
> 1. Instead of having a complex list of strings in a regex variable, it might
> be easier to hold the strings as a perl array, and then iterate over that
> array checking each element of the array on every iteration, against the
> line.
>
> 2. Roll the "\b" and/or "^" in into the regex variable itself than trying
> make them play with the variable later.
>
> 3. Use parentheses around the variable? Not sure if that will work but I
> wonder if it has something to do with operator precedence.
>
> 4. Instead of a list of paths, maybe it is better to look for "rcu" or "bpf"
> in the regex itself? That way new paths don't require script updates (at the
> expense though of false-positives (highly unlikely, IMHO)).
Given perl's tendency to have corner cases in its corner cases, I
am guessing that the "^" character combined with the "/" character is
causing trouble here. Especially given that I don't see any use of such
a pattern anywhere in checkpatch.pl except directly in a "~" expression,
and there are a lot of those.
So I will keep it as is unless I hear otherwise from Joe Perches.
Thanx, Paul
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