linux-kernel - Re: [PATCH RFC] PM: EM: Add to em_pd

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Message-ID: <819e3c75-9831-4190-aa01-e76aed423460@igalia.com>
Date: Wed, 29 Oct 2025 09:37:02 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Peng Fan <peng.fan@....com>, Lukasz Luba <lukasz.luba@....com>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@...nel.org>,
 Len Brown <lenb@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>,
 Sudeep Holla <sudeep.holla@....com>,
 Cristian Marussi <cristian.marussi@....com>
Cc: arm-scmi@...r.kernel.org, "Rafael J. Wysocki"
 <rafael.j.wysocki@...el.com>, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] PM: EM: Add to em_pd_list only when no failure

Thanks, Peng, for catching this. This makes sense.
So, feel free to add:

Reviewed-by: Changwoo Min <changwoo@...lia.com>

On 10/28/25 23:23, Peng Fan wrote:
> When em_create_perf_table() returns failure, pd is freed, there dev->em_pd
> is not valid. Then accessing dev->em_pd->node will trigger kernel panic
> in em_dev_register_pd_no_update(). So return early if 'ret' is non-zero.
> 
> Kernel dump:
> cpu cpu0: EM: invalid power: 0
> Unable to handle kernel NULL pointer dereference at virtual address
> 0000000000000008
> Mem abort info:
> pc : em_dev_register_pd_no_update+0xb4/0x79c
> lr : em_dev_register_pd_no_update+0x9c/0x79c
> Call trace:
>   em_dev_register_pd_no_update+0xb4/0x79c (P)
>   em_dev_register_perf_domain+0x18/0x58
>   scmi_cpufreq_register_em+0x84/0xb8
>   cpufreq_online+0x48c/0xb74
>   cpufreq_add_dev+0x80/0x98
>   subsys_interface_register+0x100/0x11c
>   cpufreq_register_driver+0x158/0x278
>   scmi_cpufreq_probe+0x1f8/0x2e0
>   scmi_dev_probe+0x28/0x3c
>   really_probe+0xbc/0x29c
>   __driver_probe_device+0x78/0x12c
>   driver_probe_device+0x3c/0x15c
>   __device_attach_driver+0xb8/0x134
>   bus_for_each_drv+0x84/0xe4
> 
> Fixes: cbe5aeedecc7 ("PM: EM: Assign a unique ID when creating a performance domain")
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
>   kernel/power/energy_model.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index e669d5057fca6da9612575a1c626474e60e7f7c4..11af9f64aa8276e47e0a5b2d615b227368af5480 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -693,13 +693,16 @@ int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
>   
>   unlock:
>   	mutex_unlock(&em_pd_mutex);
> +	if (ret)
> +		return ret;
>   
>   	mutex_lock(&em_pd_list_mutex);
>   	list_add_tail(&dev->em_pd->node, &em_pd_list);
>   	mutex_unlock(&em_pd_list_mutex);
>   
>   	em_notify_pd_created(dev->em_pd);
> -	return ret;
> +
> +	return 0;
>   }
>   EXPORT_SYMBOL_GPL(em_dev_register_pd_no_update);
>   
> 
> ---
> base-commit: f7d2388eeec24966fc4d5cf32d706f0514f29ac5
> change-id: 20251028-fix-energy-6b63b72ae9c6
> 
> Best regards,