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    Subject[PATCH AUTOSEL 5.4 6/8] gpio: timberdale: Fix potential deadlock on &tgpio->lock
    Date
    From: Chengfeng Ye <dg573847474@gmail.com>

    [ Upstream commit 9e8bc2dda5a7a8e2babc9975f4b11c9a6196e490 ]

    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>
    Reviewed-by: Andy Shevchenko <andy@kernel.org>
    Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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-timberdale.c
    index de14949a3fe5a..92c1f2baa4bff 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 = gpiochip_get_data(gpio);
    + unsigned long flags;
    u32 reg;

    - spin_lock(&tgpio->lock);
    + spin_lock_irqsave(&tgpio->lock, flags);
    reg = ioread32(tgpio->membase + offset);

    if (enabled)
    @@ -54,7 +55,7 @@ static int timbgpio_update_bit(struct gpio_chip *gpio, unsigned index,
    reg &= ~(1 << index);

    iowrite32(reg, tgpio->membase + offset);
    - spin_unlock(&tgpio->lock);
    + spin_unlock_irqrestore(&tgpio->lock, flags);

    return 0;
    }
    --
    2.40.1
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