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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Fri, 26 Feb 2021 10:56:43 +0100
Message-ID: <CAPDyKFq6P8-TbzqeTxfANbz4L0ezBy58O5NOQOL+qsSC=tS6oQ@mail.gmail.com>
Subject: Re: [PATCH v2] PM: runtime: Update device status before letting
 suppliers suspend
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     Linux PM <linux-pm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "elaine.zhang" <zhangqing@rock-chips.com>
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On Thu, 25 Feb 2021 at 19:23, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>
> 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>

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe

> ---
>
> v1 -> v2:
>    * Initialize the "get" variable to avoid a false-positive warning from
>      the compiler.
>
> ---
>  drivers/base/power/runtime.c |   62 +++++++++++++++++++++++++------------------
>  1 file changed, 37 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 +325,22 @@ 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;
> +       bool get = false;
> +       int retval, idx;
> +       bool 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 +355,36 @@ 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);
>         }
>
>
>