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Subject: Re: [PATCH v1] PM: runtime: Update device status before letting
 suppliers suspend
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM <linux-pm@vger.kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
References: <1930477.9OOUKYNkGr@kreacher>
From:   "elaine.zhang" <zhangqing@rock-chips.com>
Organization: rockchip
Message-ID: <c3abadb0-eaae-5dd7-3ac7-507f8e4bc5ab@rock-chips.com>
Date:   Thu, 25 Feb 2021 09:26:33 +0800
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Hi, Rafael:

在 2021/2/25 上午1:53, Rafael J. Wysocki 写道:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Because the PM-runtime status of the device is not updated in
> __rpm_callback(), attempts to suspend the suppliers of the given
> device triggered by rpm_put_suppliers() called by it may fail.
>
> Fix this by making __rpm_callback() update the device's status to
> RPM_SUSPENDED before calling rpm_put_suppliers() if the current
> status of the device is RPM_SUSPENDING and the callback just invoked
> by it has returned 0 (success).
>
> While at it, modify the code in __rpm_callback() to always check
> the device's PM-runtime status under its PM lock.
>
> Link: https://lore.kernel.org/linux-pm/CAPDyKFqm06KDw_p8WXsM4dijDbho4bb6T4k50UqqvR1_COsp8g@mail.gmail.com/
> Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
> Reported-by: elaine.zhang <zhangqing@rock-chips.com>
> Diagnosed-by: Ulf Hansson <ulf.hansson@linaro.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>
> This is different from the previously posted tentative patch, please retest.
>
> ---
>   drivers/base/power/runtime.c |   61 +++++++++++++++++++++++++------------------
>   1 file changed, 36 insertions(+), 25 deletions(-)
>
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -325,22 +325,21 @@ static void rpm_put_suppliers(struct dev
>   static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
>   	__releases(&dev->power.lock) __acquires(&dev->power.lock)
>   {
> -	int retval, idx;
>   	bool use_links = dev->power.links_count > 0;
> +	int retval, idx;
> +	bool get, put;
>   
>   	if (dev->power.irq_safe) {
>   		spin_unlock(&dev->power.lock);
> +	} else if (!use_links) {
> +		spin_unlock_irq(&dev->power.lock);
>   	} else {
> +		get = dev->power.runtime_status == RPM_RESUMING;
> +
>   		spin_unlock_irq(&dev->power.lock);
>   
> -		/*
> -		 * Resume suppliers if necessary.
> -		 *
> -		 * The device's runtime PM status cannot change until this
> -		 * routine returns, so it is safe to read the status outside of
> -		 * the lock.
> -		 */
> -		if (use_links && dev->power.runtime_status == RPM_RESUMING) {
> +		/* Resume suppliers if necessary. */
> +		if (get) {
>   			idx = device_links_read_lock();
>   
>   			retval = rpm_get_suppliers(dev);
> @@ -355,24 +354,36 @@ static int __rpm_callback(int (*cb)(stru
>   
>   	if (dev->power.irq_safe) {
>   		spin_lock(&dev->power.lock);
> -	} else {
> -		/*
> -		 * If the device is suspending and the callback has returned
> -		 * success, drop the usage counters of the suppliers that have
> -		 * been reference counted on its resume.
> -		 *
> -		 * Do that if resume fails too.
> -		 */
> -		if (use_links
> -		    && ((dev->power.runtime_status == RPM_SUSPENDING && !retval)
> -		    || (dev->power.runtime_status == RPM_RESUMING && retval))) {
> -			idx = device_links_read_lock();
> +		return retval;
> +	}
>   
> - fail:
> -			rpm_put_suppliers(dev);
> +	spin_lock_irq(&dev->power.lock);
>   
> -			device_links_read_unlock(idx);
> -		}
> +	if (!use_links)
> +		return retval;
> +
> +	/*
> +	 * If the device is suspending and the callback has returned success,
> +	 * drop the usage counters of the suppliers that have been reference
> +	 * counted on its resume.
> +	 *
> +	 * Do that if the resume fails too.
> +	 */
> +	put = dev->power.runtime_status == RPM_SUSPENDING && !retval;
> +	if (put)
> +		__update_runtime_status(dev, RPM_SUSPENDED);
> +	else
> +		put = get && retval;
> +
> +	if (put) {
> +		spin_unlock_irq(&dev->power.lock);
> +
> +		idx = device_links_read_lock();
> +
> +fail:
> +		rpm_put_suppliers(dev);
> +
> +		device_links_read_unlock(idx);
>   
>   		spin_lock_irq(&dev->power.lock);
>   	}
drivers/base/power/runtime.c: In function '__rpm_callback':
drivers/base/power/runtime.c:355:13: warning: 'get' may be used 
uninitialized in this function [-Wmaybe-uninitialized]
error, forbidden warning:runtime.c:355
    put = get && retval;

There is a compilation error. I change it as:

put = dev->power.runtime_status == RPM_SUSPENDING && retval;

And test works well.Please check it.

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