Re: [PATCH] checkpatch: ignore warning designated initializers using NR_CPUS

[Peng Wang]

Hi, Joe

On 12/30/20 1:35 PM, , Joe Perches wrote:
> On Wed, 2020-12-30 at 12:13 +0800, Peng Wang wrote:
> > Some max_length wants to hold as large room as possible to
> > ensure enough size to tackle with the biggest NR_CPUS. As
> > an example below:
> >
> > kernel/cgroup/cpuset.c:
> > static struct cftype legacy_files[] = {
> >          {
> >                  .name = "cpus",
> >                  .seq_show = cpuset_common_seq_show,
> >                  .write = cpuset_write_resmask,
> >                  .max_write_len = (100U + 6 * NR_CPUS),
> >                  .private = FILE_CPULIST,
> >          },
> > 	...
> > }
> []
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> []
> > @@ -7022,12 +7022,15 @@ sub process {
> >   
> >
> >   # use of NR_CPUS is usually wrong
> >   # ignore definitions of NR_CPUS and usage to define arrays as likely right
> > +# ignore designated initializers using NR_CPUS
> > +
> >   		if ($line =~ /\bNR_CPUS\b/ &&
> >   		    $line !~ /^.\s*\s*#\s*if\b.*\bNR_CPUS\b/ &&
> >   		    $line !~ /^.\s*\s*#\s*define\b.*\bNR_CPUS\b/ &&
> >   		    $line !~ /^.\s*$Declare\s.*\[[^\]]*NR_CPUS[^\]]*\]/ &&
> >   		    $line !~ /\[[^\]]*\.\.\.[^\]]*NR_CPUS[^\]]*\]/ &&
> > -		    $line !~ /\[[^\]]*NR_CPUS[^\]]*\.\.\.[^\]]*\]/)
> > +		    $line !~ /\[[^\]]*NR_CPUS[^\]]*\.\.\.[^\]]*\]/ &&
> > +		    $line !~ /\s*\..*=.*\bNR_CPUS\b.*,$/)
> >   		{
> >   			WARN("NR_CPUS",
> >   			     "usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc\n" . $herecurr);
>
> I wonder if it's worth it as there just aren't many of these: (6 total)

It does not look that much, but checkpatch.pl makes warning on this 
especially when "0 errors, 0 warnings" is needed.

> $ git grep -P '\..*=.*\bNR_CPUS\b.*,\s*$'
> drivers/firmware/efi/efi.c:     .cpu_bitmap             = { [BITS_TO_LONGS(NR__CPUS)] = 0},
> drivers/infiniband/hw/hfi1/sdma.c:      .max_size = NR_CPUS,
> init/init_task.c:       .nr_cpus_allowed= NR_CPUS,
> kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
> kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
> kernel/sysctl.c:                .maxlen         = NR_CPUS,
>
> It also seems it might be more sensible as:
>
> 	$line !~ /^.\s*\.\w+\s*=\s*.*\bNR_CPUS\b/

Aha, this is better!
Will send a v2 patch including this if you don't mind, Thanks.

> Which finds a couple more:
>
> $ git grep -P '^\s*\.\w+\s*=\s*.*\bNR_CPUS\b'
> arch/arm64/include/asm/processor.h:     .fpsimd_cpu = NR_CPUS,                  \
> arch/powerpc/kernel/prom_init.c:                .max_cpus = cpu_to_be32(NR_CPUS),       /* number of cores supported */
> drivers/firmware/efi/efi.c:     .cpu_bitmap             = { [BITS_TO_LONGS(NR_CPUS)] = 0},
> drivers/infiniband/hw/hfi1/sdma.c:      .max_size = NR_CPUS,
> init/init_task.c:       .nr_cpus_allowed= NR_CPUS,
> kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
> kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
> kernel/sysctl.c:                .maxlen         = NR_CPUS,