Re: [PATCH v2] RISC-V: Fix /proc/cpuinfo cpumask warning

From: Conor Dooley
Date: Wed Oct 12 2022 - 05:08:46 EST


On Wed, Oct 12, 2022 at 10:29:49AM +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. Ensure no
> warning is generated by validating the cpu index before calling
> cpumask_next().
>
> [*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.
>
> Signed-off-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> Cc: Yury Norov <yury.norov@xxxxxxxxx>

Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
Tested-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>

Thanks

> ---
> v2:
> - Got comments on the x86 equivalent patch and made the same
> changes to this one
> - Added all the information I should have in the first place
> to the commit message [Boris]
> - Changed style of fix [Boris]
>
>
> arch/riscv/kernel/cpu.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 4aa8cd749441..63138b880b92 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -166,6 +166,9 @@ static void print_mmu(struct seq_file *f)
>
> static void *c_start(struct seq_file *m, loff_t *pos)
> {
> + if (*pos >= nr_cpu_ids)
> + return NULL;
> +
> *pos = cpumask_next(*pos - 1, cpu_online_mask);
> if ((*pos) < nr_cpu_ids)
> return (void *)(uintptr_t)(1 + *pos);
> --
> 2.37.3
>