Re: [PATCH] PM / devfreq: passive: Use non-devm notifiers

[Chanwoo Choi <cw00.choi@samsung.com>]

Hi,

On 19. 8. 9. 오전 1:54, Leonard Crestez wrote:
> 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.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> 
> ---
>  drivers/devfreq/governor_passive.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> The only current user of passive governor is exynos-bus; does rmmod work
> for you? Maybe I'm missing something.
> 
> It also seems that no attempt is made to increase the ref count of
> the passive "parent" so in theory devices can be removed while still
> referenced. However that would be a separate issue.
> 
> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> index 58308948b863..da485477065c 100644
> --- a/drivers/devfreq/governor_passive.c
> +++ b/drivers/devfreq/governor_passive.c
> @@ -163,16 +163,16 @@ static int devfreq_passive_event_handler(struct devfreq *devfreq,
>  	case DEVFREQ_GOV_START:
>  		if (!p_data->this)
>  			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;
>  	}
>  
> 

Looks good to me. But, you have to add the following fixes tag
and send it to stable mailing list to fix the bug.
- Fixes: 996133119f57 ("PM / devfreq: Add new passive governor")

Acked-by: Chanwoo Choi <cw00.choi@samsung.com> 

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics