linux-kernel - [PATCH AUTOSEL 4.14 5/7] gpio: timberdale: Fix potential deadlock on &tgpio->lock

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Date:   Sat,  7 Oct 2023 20:50:51 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Chengfeng Ye <dg573847474@...il.com>,
        Andy Shevchenko <andy@...nel.org>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Sasha Levin <sashal@...nel.org>, linus.walleij@...aro.org,
        brgl@...ev.pl, linux-gpio@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 5/7] gpio: timberdale: Fix potential deadlock on &tgpio->lock

From: Chengfeng Ye <dg573847474@...il.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@...il.com>
Reviewed-by: Andy Shevchenko <andy@...nel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.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 181f86ce00cd4..639c8daaeb310 100644
--- a/drivers/gpio/gpio-timberdale.c
+++ b/drivers/gpio/gpio-timberdale.c
@@ -55,9 +55,10 @@ 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)
@@ -66,7 +67,7 @@ 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