linux-kernel - Re: [PATCH 1/2] gpio: gpio-grgpio: fix possible sleep-in-atomic-context bugs in grgpio

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Date:   Thu, 19 Dec 2019 12:10:29 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] gpio: gpio-grgpio: fix possible sleep-in-atomic-context
 bugs in grgpio_remove()

śr., 18 gru 2019 o 14:26 Jia-Ju Bai <baijiaju1990@...il.com> napisał(a):
>
> The driver may sleep while holding a spinlock.
> The function call path (from bottom to top) in Linux 4.19 is:
>
> drivers/gpio/gpiolib-sysfs.c, 796:
>         mutex_lock in gpiochip_sysfs_unregister
> drivers/gpio/gpiolib.c, 1455:
>         gpiochip_sysfs_unregister in gpiochip_remove
> drivers/gpio/gpio-grgpio.c, 460:
>         gpiochip_remove in grgpio_remove
> drivers/gpio/gpio-grgpio.c, 449:
>         _raw_spin_lock_irqsave in grgpio_remove
>
> kernel/irq/irqdomain.c, 243:
>         mutex_lock in irq_domain_remove
> drivers/gpio/gpio-grgpio.c, 463:
>         irq_domain_remove in grgpio_remove
> drivers/gpio/gpio-grgpio.c, 449:
>         _raw_spin_lock_irqsave in grgpio_remove
>
> mutex_lock() can sleep at runtime.
>
> To fix these bugs, gpiochip_remove() and irq_domain_remove() are called
> without holding the spinlock.
>
> These bugs are found by a static analysis tool STCheck written by myself.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  drivers/gpio/gpio-grgpio.c      | 5 ++++-
>  sound/soc/sti/uniperif_player.c | 3 ++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpio-grgpio.c b/drivers/gpio/gpio-grgpio.c
> index 08234e64993a..60a2871c5ba7 100644
> --- a/drivers/gpio/gpio-grgpio.c
> +++ b/drivers/gpio/gpio-grgpio.c
> @@ -448,13 +448,16 @@ static int grgpio_remove(struct platform_device *ofdev)
>                 }
>         }
>
> +       spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);
> +
>         gpiochip_remove(&priv->gc);
>
>         if (priv->domain)
>                 irq_domain_remove(priv->domain);
>
>  out:
> -       spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);
> +       if (ret)
> +               spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);

In general there is no need for locking in remove() callbacks. I guess
you can safely remove the spinlock here all together.

>
>         return ret;
>  }
> diff --git a/sound/soc/sti/uniperif_player.c b/sound/soc/sti/uniperif_player.c
> index 48ea915b24ba..62244e207679 100644
> --- a/sound/soc/sti/uniperif_player.c
> +++ b/sound/soc/sti/uniperif_player.c
> @@ -601,13 +601,14 @@ static int uni_player_ctl_iec958_put(struct snd_kcontrol *kcontrol,
>         mutex_unlock(&player->ctrl_lock);
>
>         spin_lock_irqsave(&player->irq_lock, flags);
> +       spin_unlock_irqrestore(&player->irq_lock, flags);

Yeah I can tell this was generated automatically - what does this line
is expected to achieve?

Bart

> +
>         if (player->substream && player->substream->runtime)
>                 uni_player_set_channel_status(player,
>                                               player->substream->runtime);
>         else
>                 uni_player_set_channel_status(player, NULL);
>
> -       spin_unlock_irqrestore(&player->irq_lock, flags);
>         return 0;
>  }
>
> --
> 2.17.1
>