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

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Message-Id: <20191218132605.10594-1-baijiaju1990@gmail.com>
Date:   Wed, 18 Dec 2019 21:26:05 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     linus.walleij@...aro.org, bgolaszewski@...libre.com
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH 2/2] gpio: gpio-grgpio: fix possible sleep-in-atomic-context bugs in grgpio_irq_map/unmap()

The driver may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

drivers/gpio/gpio-grgpio.c, 261: 
	request_irq in grgpio_irq_map
drivers/gpio/gpio-grgpio.c, 255: 
	_raw_spin_lock_irqsave in grgpio_irq_map

drivers/gpio/gpio-grgpio.c, 318: 
	free_irq in grgpio_irq_unmap
drivers/gpio/gpio-grgpio.c, 299: 
	_raw_spin_lock_irqsave in grgpio_irq_unmap

request_irq() and free_irq() can sleep at runtime.

To fix these bugs, request_irq() and free_irq() 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 | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpio/gpio-grgpio.c b/drivers/gpio/gpio-grgpio.c
index 08234e64993a..3224933f4c8f 100644
--- a/drivers/gpio/gpio-grgpio.c
+++ b/drivers/gpio/gpio-grgpio.c
@@ -253,17 +253,16 @@ static int grgpio_irq_map(struct irq_domain *d, unsigned int irq,
 	lirq->irq = irq;
 	uirq = &priv->uirqs[lirq->index];
 	if (uirq->refcnt == 0) {
+		spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);
 		ret = request_irq(uirq->uirq, grgpio_irq_handler, 0,
 				  dev_name(priv->dev), priv);
 		if (ret) {
 			dev_err(priv->dev,
 				"Could not request underlying irq %d\n",
 				uirq->uirq);
-
-			spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);
-
 			return ret;
 		}
+		spin_lock_irqsave(&priv->gc.bgpio_lock, flags);
 	}
 	uirq->refcnt++;
 
@@ -309,8 +308,11 @@ static void grgpio_irq_unmap(struct irq_domain *d, unsigned int irq)
 	if (index >= 0) {
 		uirq = &priv->uirqs[lirq->index];
 		uirq->refcnt--;
-		if (uirq->refcnt == 0)
+		if (uirq->refcnt == 0) {
+			spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);
 			free_irq(uirq->uirq, priv);
+			return;
+		}
 	}
 
 	spin_unlock_irqrestore(&priv->gc.bgpio_lock, flags);
-- 
2.17.1