linux-kernel - Re: [PATCH] PM: runtime: Simplify locking in pm_runtime_put

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Date:   Tue, 21 Dec 2021 12:46:44 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PM: runtime: Simplify locking in pm_runtime_put_suppliers()

On Fri, 17 Dec 2021 at 20:16, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Notice that pm_runtime_put_suppliers() cannot be called with
> disabled interrupts, because it may sleep (due to the device
> links read locking in the non-SRCU case), and so it can use
> spin_lock_irq() and spin_unlock_irq() for the locking.
>
> Update the function accordingly and while at it move the "put"
> local variable in it into the inner block where it is used.
>
> This change is not expected to have any visible functional impact.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

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

Kind regards
Uffe

> ---
>  drivers/base/power/runtime.c |   12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -1748,8 +1748,6 @@ void pm_runtime_get_suppliers(struct dev
>  void pm_runtime_put_suppliers(struct device *dev)
>  {
>         struct device_link *link;
> -       unsigned long flags;
> -       bool put;
>         int idx;
>
>         idx = device_links_read_lock();
> @@ -1757,11 +1755,17 @@ void pm_runtime_put_suppliers(struct dev
>         list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
>                                 device_links_read_lock_held())
>                 if (link->supplier_preactivated) {
> +                       bool put;
> +
>                         link->supplier_preactivated = false;
> -                       spin_lock_irqsave(&dev->power.lock, flags);
> +
> +                       spin_lock_irq(&dev->power.lock);
> +
>                         put = pm_runtime_status_suspended(dev) &&
>                               refcount_dec_not_one(&link->rpm_active);
> -                       spin_unlock_irqrestore(&dev->power.lock, flags);
> +
> +                       spin_unlock_irq(&dev->power.lock);
> +
>                         if (put)
>                                 pm_runtime_put(link->supplier);
>                 }
>
>
>