Re: [PATCH] thermal/drivers/intel_powerclamp: Fix bug for smp_processor_id

[Rafael J. Wysocki]

On Tue, Sep 20, 2022 at 1:07 PM Srinivas Pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> wrote:
>
> When CPU 0 is offline and intel_powerclamp is used to inject
> idle, it generates kernel BUG:
>
> BUG: using smp_processor_id() in preemptible [00000000] code: bash/15687
> caller is debug_smp_processor_id+0x17/0x20
> CPU: 4 PID: 15687 Comm: bash Not tainted 5.19.0-rc7+ #57
> Call Trace:
> <TASK>
> dump_stack_lvl+0x49/0x63
> dump_stack+0x10/0x16
> check_preemption_disabled+0xdd/0xe0
> debug_smp_processor_id+0x17/0x20
> powerclamp_set_cur_state+0x7f/0xf9 [intel_powerclamp]
> ...
> ...
>
> Here CPU 0 is the control CPU by default and changed to the current CPU,
> if CPU 0 offlined. This check has to be performed under cpus_read_lock(),
> hence the above warning.
>
> Use get_cpu() instead of smp_processor_id() to avoid this BUG.
>
> Suggested-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> ---
>  drivers/thermal/intel/intel_powerclamp.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/thermal/intel/intel_powerclamp.c b/drivers/thermal/intel/intel_powerclamp.c
> index c841ab37e7c6..46cd799af148 100644
> --- a/drivers/thermal/intel/intel_powerclamp.c
> +++ b/drivers/thermal/intel/intel_powerclamp.c
> @@ -532,8 +532,10 @@ static int start_power_clamp(void)
>
>         /* prefer BSP */
>         control_cpu = 0;
> -       if (!cpu_online(control_cpu))
> -               control_cpu = smp_processor_id();
> +       if (!cpu_online(control_cpu)) {
> +               control_cpu = get_cpu();
> +               put_cpu();
> +       }
>
>         clamping = true;
>         schedule_delayed_work(&poll_pkg_cstate_work, 0);
> --

Applied as 6.1 material with modified subject, thanks!