linux-kernel - Re: [PATCH AUTOSEL 4.19 075/128] PM / devfreq: passive: Use non-devm notifiers

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Date:   Mon, 23 Sep 2019 20:38:53 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Sasha Levin <sashal@...nel.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL 4.19 075/128] PM / devfreq: passive: Use non-devm
 notifiers

On 22.09.2019 21:56, Sasha Levin wrote:
> From: Leonard Crestez <leonard.crestez@....com>
> 
> [ Upstream commit 0ef7c7cce43f6ecc2b96d447e69b2900a9655f7c ]

This will introduce an "unused variable warning" unless you also 
cherry-pick commit 0465814831a9 ("PM / devfreq: passive: fix compiler 
warning").

> The devfreq passive governor registers and unregisters devfreq
> transition notifiers on DEVFREQ_GOV_START/GOV_STOP using devm wrappers.
> 
> If devfreq itself is registered with devm then a warning is triggered on
> rmmod from devm_devfreq_unregister_notifier. Call stack looks like this:
> 
> 	devm_devfreq_unregister_notifier+0x30/0x40
> 	devfreq_passive_event_handler+0x4c/0x88
> 	devfreq_remove_device.part.8+0x6c/0x9c
> 	devm_devfreq_dev_release+0x18/0x20
> 	release_nodes+0x1b0/0x220
> 	devres_release_all+0x78/0x84
> 	device_release_driver_internal+0x100/0x1c0
> 	driver_detach+0x4c/0x90
> 	bus_remove_driver+0x7c/0xd0
> 	driver_unregister+0x2c/0x58
> 	platform_driver_unregister+0x10/0x18
> 	imx_devfreq_platdrv_exit+0x14/0xd40 [imx_devfreq]
> 
> This happens because devres_release_all will first remove all the nodes
> into a separate todo list so the nested devres_release from
> devm_devfreq_unregister_notifier won't find anything.
> 
> Fix the warning by calling the non-devm APIS for frequency notification.
> Using devm wrappers is not actually useful for a governor anyway: it
> relies on the devfreq core to correctly match the GOV_START/GOV_STOP
> notifications.
> 
> Fixes: 996133119f57 ("PM / devfreq: Add new passive governor")
> Signed-off-by: Leonard Crestez <leonard.crestez@....com>
> Acked-by: Chanwoo Choi <cw00.choi@...sung.com>
> Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>   drivers/devfreq/governor_passive.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> index 3bc29acbd54e8..22fd41b4c1098 100644
> --- a/drivers/devfreq/governor_passive.c
> +++ b/drivers/devfreq/governor_passive.c
> @@ -168,12 +168,12 @@ static int devfreq_passive_event_handler(struct devfreq *devfreq,
>   			p_data->this = devfreq;
>   
>   		nb->notifier_call = devfreq_passive_notifier_call;
> -		ret = devm_devfreq_register_notifier(dev, parent, nb,
> +		ret = devfreq_register_notifier(parent, nb,
>   					DEVFREQ_TRANSITION_NOTIFIER);
>   		break;
>   	case DEVFREQ_GOV_STOP:
> -		devm_devfreq_unregister_notifier(dev, parent, nb,
> -					DEVFREQ_TRANSITION_NOTIFIER);
> +		WARN_ON(devfreq_unregister_notifier(parent, nb,
> +					DEVFREQ_TRANSITION_NOTIFIER));
>   		break;
>   	default:
>   		break;
>