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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 20 Apr 2022 18:23:48 +0200
Message-ID: <CAJZ5v0h2SWN-=-5=OsMGm1amMJrYELqM6BC+J=98EAxSUmxMqg@mail.gmail.com>
Subject: Re: [PATCH 6/9] pm/irq: make for_each_irq_desc() safe of irq_desc release
To:     Pingfan Liu <kernelfans@gmail.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Rafael J. Wysocki" <rafael@kernel.org>
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On Wed, Apr 20, 2022 at 4:06 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> The invloved context is no a RCU read section. Furthermore there may be
> more than one task at this point. Hence it demands a measure to prevent
> irq_desc from freeing. Use irq_lock_sparse to serve the protection
> purpose.

Can you please describe an example scenario in which the added locking
will prevent a failure from occurring?

> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> To: linux-kernel@vger.kernel.org
> ---
>  kernel/irq/pm.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
> index ca71123a6130..4b67a4c7de3c 100644
> --- a/kernel/irq/pm.c
> +++ b/kernel/irq/pm.c
> @@ -133,6 +133,7 @@ void suspend_device_irqs(void)
>         struct irq_desc *desc;
>         int irq;
>
> +       irq_lock_sparse();
>         for_each_irq_desc(irq, desc) {
>                 unsigned long flags;
>                 bool sync;
> @@ -146,6 +147,7 @@ void suspend_device_irqs(void)
>                 if (sync)
>                         synchronize_irq(irq);
>         }
> +       irq_unlock_sparse();
>  }
>  EXPORT_SYMBOL_GPL(suspend_device_irqs);
>
> @@ -186,6 +188,7 @@ static void resume_irqs(bool want_early)
>         struct irq_desc *desc;
>         int irq;
>
> +       /* The early resume stage is free of irq_desc release */
>         for_each_irq_desc(irq, desc) {
>                 unsigned long flags;
>                 bool is_early = desc->action &&
> --
> 2.31.1
>