gpiolib: don't call sleeping functions with a spinlock taken

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@linux-m68k.org>
Fixes: d2ac257 ("gpiolib: provide a dedicated function for setting lineinfo")
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>

Author: brgl

drivers/gpio/gpiolib.c

@@ -1158,8 +1158,19 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 				  struct gpioline_info *info)
 {
 	struct gpio_chip *gc = 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(gc->base + info->line_offset);
+
 	spin_lock_irqsave(&gpio_lock, flags);
 
 	if (desc->name) {
@@ -1186,7 +1197,7 @@ 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(gc->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;