Re: [PATCH v3 0/2] Fix /proc/cpuinfo cpumask warning

Palmer Dabbelt
2022-10-27T23:07:24Z

On Fri, 14 Oct 2022 08:58:43 PDT (-0700), ajones@ventanamicro.com 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.
>
> v3:
> - Change condition from >= to == in order to still get a warning
> for > as that's unexpected. [Yury]
> - Picked up tags on the riscv patch
>
> v2:
> - Added all the information I should have in the first place
> to the commit message [Boris]
> - Changed style of fix [Boris]
>
> Andrew Jones (2):
> RISC-V: Fix /proc/cpuinfo cpumask warning

I just took the RISC-V fix, might be worth re-sending the x86 one alone
as nobody's replied over there so it may be lost.

Thanks!

> x86: Fix /proc/cpuinfo cpumask warning
>
> arch/riscv/kernel/cpu.c | 3 +++
> arch/x86/kernel/cpu/proc.c | 3 +++
> 2 files changed, 6 insertions(+)