linux-kernel - Re: [PATCH tip/core/rcu 20/21] checkpatch: Add warnings for {smp_,}read_barrier

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Message-ID: <1512189913.19952.184.camel@perches.com>
Date:   Fri, 01 Dec 2017 20:45:13 -0800
From:   Joe Perches <joe@...ches.com>
To:     paulmck@...ux.vnet.ibm.com
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        Andy Whitcroft <apw@...onical.com>
Subject: Re: [PATCH tip/core/rcu 20/21] checkpatch: Add warnings for
 {smp_,}read_barrier_depends()

On Fri, 2017-12-01 at 13:44 -0800, Paul E. McKenney wrote:
> On Fri, Dec 01, 2017 at 12:14:17PM -0800, Joe Perches wrote:
> > On Fri, 2017-12-01 at 11:51 -0800, Paul E. McKenney wrote:
> > > Now that both smp_read_barrier_depends() and read_barrier_depends()
> > > are being de-emphasized, warn if any are added.
> > 
> > This would also warn on existing files when run
> > with ./scripts/checkpatch.pl -f <file>
> > 
> > Do you want it to check new patches only?
> > 
> > If so the test could become "if (!$file && etc...)
> > 
> > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> > > @@ -5586,6 +5586,12 @@ sub process {
> > >  			}
> > >  		}
> > >  
> > > +# check for smp_read_barrier_depends and read_barrier_depends
> > > +		if ($line =~ /\b(smp_|)read_barrier_depends\(/) {
> > 
> > Must become
> > 
> > +		if ($line =~ /\b(smp_|)read_barrier_depends\s*\(/) {
> > 
> > similar to the lines above this as there are sometimes
> > spaces between function name and argument parentheses.
> 
> Good points!  Like this?
[]
> commit ff155ce179aab891dbe2ca80f82a453383fd165a
> Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Date:   Mon Nov 27 09:37:35 2017 -0800
> 
>     checkpatch: Add warnings for {smp_,}read_barrier_depends()
>     
>     Now that both smp_read_barrier_depends() and read_barrier_depends()
>     are being de-emphasized, warn if any are added.
>     
>     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>     Cc: Andy Whitcroft <apw@...onical.com>
>     Cc: Joe Perches <joe@...ches.com>
>     [ paulmck: Skipped checking files and handled whitespace per Joe Perches. ]
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -5586,6 +5586,12 @@ sub process {
>  			}
>  		}
>  
> +# check for smp_read_barrier_depends and read_barrier_depends
> +		if (!$file && $line =~ /\b(smp_|)read_barrier_depends\s*\(/) {
> +			WARN("READ_BARRIER_DEPENDS",
> +			     "Dependency barriers should only be used in READ_ONCE or DEC Alpha code" . $herecurr);

Almost right.  Missing a '\n' after "DEC Alpha code".
Without the '\n', running checkpatch with --terse outputs badly.

If you really wanted to optimize, you could make the first (smp_|)
become (?:smp_|) to avoid the unused capture group.
Or perhaps this could emit the actual type in the message like:

		if (!$file && $line =~ /\b((?:smp_|)read_barrier_depends)\s*\(/ {
			WARN("READ_BARRIER_DEPENDS",
			     "$1 should only be used in READ_ONCE or DEC Alpha code\n" . $herecurr);