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Subject: Re: [PATCH] checkpatch: ignore warning designated initializers
 using NR_CPUS
From:   Joe Perches <joe@perches.com>
To:     Peng Wang <rocking@linux.alibaba.com>, apw@canonical.com
Cc:     linux-kernel@vger.kernel.org
Date:   Tue, 29 Dec 2020 21:35:13 -0800
In-Reply-To: <2eba2ec8531f440410ee8164aaf2ab754bd5a0d1.1609301434.git.rocking@linux.alibaba.com>
References: <2eba2ec8531f440410ee8164aaf2ab754bd5a0d1.1609301434.git.rocking@linux.alibaba.com>
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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)

$ 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/

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,