On Fri, Oct 14, 2022 at 05:58:43PM +0200, Andrew Jones wrote:

Commit 78e5a3399421 ("cpumask: fix checking valid cpu range") has
started issuing warnings[*] when cpu indices equal to nr_cpu_ids - 1
are passed to cpumask_next* functions. seq_read_iter() and cpuinfo's
start and next seq operations implement a pattern like

  n = cpumask_next(n - 1, mask);
  show(n);
  while (1) {
      ++n;
      n = cpumask_next(n - 1, mask);
      if (n >= nr_cpu_ids)
          break;
      show(n);
  }
    
which will issue the warning when reading /proc/cpuinfo.

[*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.

This series address the issue for x86 and riscv, but from a quick
grep of cpuinfo seq operations, I think at least openrisc, powerpc,
and s390 also need an equivalent patch. While the test is simple (see
next paragraph) I'm not equipped to test on each architecture.

To test, just build a kernel with DEBUG_PER_CPU_MAPS enabled, boot to
a shell, do 'cat /proc/cpuinfo', and look for a kernel warning.

While the patches are being posted together in a series since they're
for two different architectures they don't necessarily need to go
through the same tree.

Acked-by: Yury Norov <yury.norov@gmail.com