linux-kernel - Re: [PATCH] cpuidle: psci: Iterate backwards over list in psci_pd

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Date:   Fri, 25 Feb 2022 16:30:42 +0800
From:   Shawn Guo <shawn.guo@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Ulf Hansson <ulf.hansson@...aro.org>, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpuidle: psci: Iterate backwards over list in
 psci_pd_remove()

On Fri, Feb 25, 2022 at 04:24:20PM +0800, Shawn Guo wrote:
> In case that psci_pd_init_topology() fails for some reason,
> psci_pd_remove() will be responsible for deleting provider and removing
> genpd from psci_pd_providers list.  There will be a failure when removing
> the cluster PD, because the cpu (child) PDs haven't been removed.
> 
> [    0.050232] CPUidle PSCI: init PM domain cpu0
> [    0.050278] CPUidle PSCI: init PM domain cpu1
> [    0.050329] CPUidle PSCI: init PM domain cpu2
> [    0.050370] CPUidle PSCI: init PM domain cpu3
> [    0.050422] CPUidle PSCI: init PM domain cpu-cluster0
> [    0.050475] PM: genpd_remove: unable to remove cpu-cluster0
> [    0.051412] PM: genpd_remove: removed cpu3
> [    0.051449] PM: genpd_remove: removed cpu2
> [    0.051499] PM: genpd_remove: removed cpu1
> [    0.051546] PM: genpd_remove: removed cpu0
> 
> Fix the problem by iterating the provider list in a reversely order, so

s/reversely/reversed

> that parent PD gets removed before child's PDs.

s/before/after

Essentially, with this change, the PM domains will be removed in the same
order how they were added.

[    0.029052] CPUidle PSCI: init PM domain cpu0
[    0.029076] CPUidle PSCI: init PM domain cpu1
[    0.029103] CPUidle PSCI: init PM domain cpu2
[    0.029124] CPUidle PSCI: init PM domain cpu3
[    0.029151] CPUidle PSCI: init PM domain cpu-cluster0
[    0.029647] PM: genpd_remove: removed cpu0
[    0.029666] PM: genpd_remove: removed cpu1
[    0.029690] PM: genpd_remove: removed cpu2
[    0.029714] PM: genpd_remove: removed cpu3
[    0.029738] PM: genpd_remove: removed cpu-cluster0

Shawn

> 
> Signed-off-by: Shawn Guo <shawn.guo@...aro.org>
> ---
>  drivers/cpuidle/cpuidle-psci-domain.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
> index ff2c3f8e4668..ce5c415fb04d 100644
> --- a/drivers/cpuidle/cpuidle-psci-domain.c
> +++ b/drivers/cpuidle/cpuidle-psci-domain.c
> @@ -182,7 +182,8 @@ static void psci_pd_remove(void)
>  	struct psci_pd_provider *pd_provider, *it;
>  	struct generic_pm_domain *genpd;
>  
> -	list_for_each_entry_safe(pd_provider, it, &psci_pd_providers, link) {
> +	list_for_each_entry_safe_reverse(pd_provider, it,
> +					 &psci_pd_providers, link) {
>  		of_genpd_del_provider(pd_provider->node);
>  
>  		genpd = of_genpd_remove_last(pd_provider->node);
> -- 
> 2.25.1
>