linux-kernel - [PATCH] gpiolib: don't call sleeping functions with a spinlock taken

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Message-Id: <20200320093125.23092-1-brgl@bgdev.pl>
Date:   Fri, 20 Mar 2020 10:31:25 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: [PATCH] gpiolib: don't call sleeping functions with a spinlock taken

From: Bartosz Golaszewski <bgolaszewski@...libre.com>

We must not call pinctrl_gpio_can_use_line() with the gpio_lock taken
as it takes a mutex internally. Let's move the call before taking the
spinlock and store the return value.

This isn't perfect - there's a moment between calling
pinctrl_gpio_can_use_line() and taking the spinlock where the situation
can change but it isn't a regression either: previously this part wasn't
protected at all and it only affects the information user-space is
seeing.

Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Fixes: d2ac25798208 ("gpiolib: provide a dedicated function for setting lineinfo")
Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
---
 drivers/gpio/gpiolib.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 02f8b2b81199..ee20634a522c 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1154,8 +1154,19 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 				  struct gpioline_info *info)
 {
 	struct gpio_chip *chip = desc->gdev->chip;
+	bool ok_for_pinctrl;
 	unsigned long flags;
 
+	/*
+	 * This function takes a mutex so we must check this before taking
+	 * the spinlock.
+	 *
+	 * FIXME: find a non-racy way to retrieve this information. Maybe a
+	 * lock common to both frameworks?
+	 */
+	ok_for_pinctrl = pinctrl_gpio_can_use_line(
+				chip->base + info->line_offset);
+
 	spin_lock_irqsave(&gpio_lock, flags);
 
 	if (desc->name) {
@@ -1182,7 +1193,7 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 	    test_bit(FLAG_USED_AS_IRQ, &desc->flags) ||
 	    test_bit(FLAG_EXPORT, &desc->flags) ||
 	    test_bit(FLAG_SYSFS, &desc->flags) ||
-	    !pinctrl_gpio_can_use_line(chip->base + info->line_offset))
+	    !ok_for_pinctrl)
 		info->flags |= GPIOLINE_FLAG_KERNEL;
 	if (test_bit(FLAG_IS_OUT, &desc->flags))
 		info->flags |= GPIOLINE_FLAG_IS_OUT;
-- 
2.25.0