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References: <20230926102914.6145-1-dg573847474@gmail.com>
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From:   Bartosz Golaszewski <brgl@bgdev.pl>
Date:   Wed, 27 Sep 2023 08:52:01 +0200
Message-ID: <CAMRc=Mf-tO5yaushz__Mq+em8o3Qp+QkG2Dc06JY9r-GoWPu=Q@mail.gmail.com>
Subject: Re: [PATCH] gpio: timberdale: Fix potential deadlock on &tgpio->lock
To:     Chengfeng Ye <dg573847474@gmail.com>
Cc:     linus.walleij@linaro.org, andy@kernel.org, alex@shruggie.ro,
        aboutphysycs@gmail.com, linux-gpio@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Tue, Sep 26, 2023 at 12:29=E2=80=AFPM Chengfeng Ye <dg573847474@gmail.co=
m> wrote:
>
> As timbgpio_irq_enable()/timbgpio_irq_disable() callback could be
> executed under irq context, it could introduce double locks on
> &tgpio->lock if it preempts other execution units requiring
> the same locks.
>
> timbgpio_gpio_set()
> --> timbgpio_update_bit()
> --> spin_lock(&tgpio->lock)
> <interrupt>
>    --> timbgpio_irq_disable()
>    --> spin_lock_irqsave(&tgpio->lock)
>
> This flaw was found by an experimental static analysis tool I am
> developing for irq-related deadlock.
>
> To prevent the potential deadlock, the patch uses spin_lock_irqsave()
> on &tgpio->lock inside timbgpio_gpio_set() to prevent the possible
> deadlock scenario.
>
> Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
> ---
>  drivers/gpio/gpio-timberdale.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpio-timberdale.c b/drivers/gpio/gpio-timberdal=
e.c
> index bbd9e9191199..fad979797486 100644
> --- a/drivers/gpio/gpio-timberdale.c
> +++ b/drivers/gpio/gpio-timberdale.c
> @@ -43,9 +43,10 @@ static int timbgpio_update_bit(struct gpio_chip *gpio,=
 unsigned index,
>         unsigned offset, bool enabled)
>  {
>         struct timbgpio *tgpio =3D gpiochip_get_data(gpio);
> +       unsigned long flags;
>         u32 reg;
>
> -       spin_lock(&tgpio->lock);
> +       spin_lock_irqsave(&tgpio->lock, flags);
>         reg =3D ioread32(tgpio->membase + offset);
>
>         if (enabled)
> @@ -54,7 +55,7 @@ static int timbgpio_update_bit(struct gpio_chip *gpio, =
unsigned index,
>                 reg &=3D ~(1 << index);
>
>         iowrite32(reg, tgpio->membase + offset);
> -       spin_unlock(&tgpio->lock);
> +       spin_unlock_irqrestore(&tgpio->lock, flags);
>
>         return 0;
>  }
> --
> 2.17.1
>

Applied, thanks!

Bart