linux-kernel - Re: [PATCH v1 1/6] perf header: Replace hardcoded max cpus by MAX_NR

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Message-ID: <aXpSSaMdBhKDRzsY@x1>
Date: Wed, 28 Jan 2026 15:15:37 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Swapnil Sapkal <swapnil.sapkal@....com>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	adrian.hunter@...el.com, thomas.falcon@...el.com,
	ashelat@...hat.com, yu.c.chen@...el.com, gautham.shenoy@....com,
	ravi.bangoria@....com, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, peterz@...radead.org,
	mingo@...hat.com, namhyung@...nel.org, irogers@...gle.com,
	james.clark@....com
Subject: Re: [PATCH v1 1/6] perf header: Replace hardcoded max cpus by
 MAX_NR_CPUS

On Wed, Jan 28, 2026 at 09:55:05PM +0530, Swapnil Sapkal wrote:
> Hi Srikanth, Arnaldo,
> 
> Thank you for reviewing the patches.
> 
> On 28-01-2026 13:09, Shrikanth Hegde wrote:
> > 
> > 
> > On 1/28/26 12:19 AM, Swapnil Sapkal wrote:
> > > cpumask and cpulist from cpu-domain header have hardcoded max_cpus value
> > > of 1024. Current systems have more cpus than this value. Replace it with
> > > MAX_NR_CPUS. Also define a macro to represent domain name length.
> > > 
> > > Fixes: d40c68a49f69 ("perf header: Support CPU DOMAIN relation info")
> > > Reported-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
> > > Signed-off-by: Swapnil Sapkal <swapnil.sapkal@....com>
> > > ---
> > >   tools/perf/util/header.c | 5 +++--
> > >   1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> > > index eefd1cd73b6a..31c3bab1b10a 100644
> > > --- a/tools/perf/util/header.c
> > > +++ b/tools/perf/util/header.c
> > > @@ -76,6 +76,7 @@ static const u64 __perf_magic2    =
> > > 0x32454c4946524550ULL;
> > >   static const u64 __perf_magic2_sw = 0x50455246494c4532ULL;
> > >   #define PERF_MAGIC    __perf_magic2
> > > +#define DNAME_LEN    16
> > >   const char perf_version_string[] = PERF_VERSION;
> > > @@ -1616,10 +1617,10 @@ static int write_pmu_caps(struct feat_fd *ff,
> > >   struct cpu_domain_map **build_cpu_domain_map(u32
> > > *schedstat_version, u32 *max_sched_domains, u32 nr)
> > >   {
> > > +    char dname[DNAME_LEN], cpumask[MAX_NR_CPUS];
> > >       struct domain_info *domain_info;
> > >       struct cpu_domain_map **cd_map;
> > > -    char dname[16], cpumask[256];
> > > -    char cpulist[1024];
> > > +    char cpulist[MAX_NR_CPUS];
> > >       char *line = NULL;
> > >       u32 cpu, domain;
> > >       u32 dcount = 0;
> > 
> > Looking at
> > https://lore.kernel.org/all/20260119175833.340369-3-swapnil.sapkal@amd.com/
> > 
> > There was one more "char cpus[1024]"  in tools/perf/util/util.c.
> > You may need to fix that too. It is unlikely but, if one has created
> > exclusive
> > cpusets comprising of only one cpu from a core, maybe you will run out
> > the length.
> > So better use the MAX_NR_CPUS there as well.
> 
> Yes, I missed this.
> 
> Arnaldo, can you please consider the below diff? Let me know if you'd like
> me to respin the patch.
> 
> --
> Thanks and Regards,
> Swapnil
> 
> diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
> index c83e59e8c787..3795d5182ce8 100644
> --- a/tools/perf/util/util.c
> +++ b/tools/perf/util/util.c
> @@ -262,7 +262,7 @@ void cpumask_to_cpulist(char *cpumask, char *cpulist)
>         int i, j, bm_size, nbits;
>         int len = strlen(cpumask);
>         unsigned long *bm;
> -       char cpus[1024];
> +       char cpus[MAX_NR_CPUS];
> 
>         for (i = 0; i < len; i++) {
>                 if (cpumask[i] == ',') {
> diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
> index 394dbfa944ac..c43f17137efd 100644
> --- a/tools/perf/util/util.h
> +++ b/tools/perf/util/util.h
> @@ -6,6 +6,7 @@
>  /* glibc 2.20 deprecates _BSD_SOURCE in favour of _DEFAULT_SOURCE */
>  #define _DEFAULT_SOURCE 1
> 
> +#include "perf.h"

Why add it to util.h? I'll add it to where it is used, util.c, ok?

- Arnaldo

>  #include <dirent.h>
>  #include <fcntl.h>
>  #include <stdbool.h>