linux-kernel - Re: [PATCH v1 01/12] PM: sleep: Simplify dpm_suspended_list walk in dpm

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Date: Thu, 25 Jan 2024 08:40:33 +0100
From: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v1 01/12] PM: sleep: Simplify dpm_suspended_list walk in
 dpm_resume()

On Mon, Jan 22, 2024 at 12:22:38PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Notice that devices can be moved to dpm_prepared_list before running
> their resume callbacks, in analogy with dpm_noirq_resume_devices() and
> dpm_resume_early(), because doing so will not affect the final ordering
> of that list.
> 
> Namely, if a device is the first dpm_suspended_list entry while
> dpm_list_mtx is held, it has not been removed so far and it cannot be
> removed until dpm_list_mtx is released, so moving it to dpm_prepared_list
> at that point is valid.  If it is removed later, while its resume
> callback is running, it will be deleted from dpm_prepared_list without
> changing the ordering of the other devices in that list.
> 
> Accordingly, rearrange the while () loop in dpm_resume() to move
> devices to dpm_prepared_list before running their resume callbacks and
> implify the locking and device reference counting in it.
> 
> No intentional functional impact.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>

> ---
>  drivers/base/power/main.c |   16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> Index: linux-pm/drivers/base/power/main.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/main.c
> +++ linux-pm/drivers/base/power/main.c
> @@ -1017,25 +1017,19 @@ void dpm_resume(pm_message_t state)
>  
>  	while (!list_empty(&dpm_suspended_list)) {
>  		dev = to_device(dpm_suspended_list.next);
> -
> -		get_device(dev);
> +		list_move_tail(&dev->power.entry, &dpm_prepared_list);
>  
>  		if (!dev->power.async_in_progress) {
> +			get_device(dev);
> +
>  			mutex_unlock(&dpm_list_mtx);
>  
>  			device_resume(dev, state, false);
>  
> +			put_device(dev);
> +
>  			mutex_lock(&dpm_list_mtx);
>  		}
> -
> -		if (!list_empty(&dev->power.entry))
> -			list_move_tail(&dev->power.entry, &dpm_prepared_list);
> -
> -		mutex_unlock(&dpm_list_mtx);
> -
> -		put_device(dev);
> -
> -		mutex_lock(&dpm_list_mtx);
>  	}
>  	mutex_unlock(&dpm_list_mtx);
>  	async_synchronize_full();
> 
> 
>