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

[Joe Perches]

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@xxxxxxxxxxxxx> (maintainer:CHECKPATCH)
> > > Cc: Joe Perches <joe@xxxxxxxxxxx> (maintainer:CHECKPATCH)
> > > Cc: Dwaipayan Ray <dwaipayanray1@xxxxxxxxx> (reviewer:CHECKPATCH)
> > > Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
> > > Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> > > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > > Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> > > Cc: <bpf@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > > ---
> > >  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.

> > 	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