[PATCH v3] gpiolib: fix reference leaks when removing GPIO chips still in use

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

After we remove a GPIO chip that still has some requested descriptors,
gpiod_free_commit() will fail and we will never put the references to the
GPIO device and the owning module in gpiod_free().

Rework this function to:
- not warn on desc == NULL as this is a use-case on which most free
  functions silently return
- put the references to desc->gdev and desc->gdev->owner unconditionally
  so that the release callback actually gets called when the remaining
  references are dropped by external GPIO users

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
v1 -> v2:
- add a comment about why we can't use VALIDATE_DESC_VOID()

v2 -> v3:
- we must drop the reference to the owner module before we drop the one
  to the gpio_device as the latter may be removed if this is the last
  reference and we'll end up calling module_put() on freed memory

 drivers/gpio/gpiolib.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 251c875b5c34..76e0c38026c3 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2167,12 +2167,18 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
 
 void gpiod_free(struct gpio_desc *desc)
 {
-	if (desc && desc->gdev && gpiod_free_commit(desc)) {
-		module_put(desc->gdev->owner);
-		gpio_device_put(desc->gdev);
-	} else {
+	/*
+	 * We must not use VALIDATE_DESC_VOID() as the underlying gdev->chip
+	 * may already be NULL but we still want to put the references.
+	 */
+	if (!desc)
+		return;
+
+	if (!gpiod_free_commit(desc))
 		WARN_ON(extra_checks);
-	}
+
+	module_put(desc->gdev->owner);
+	gpio_device_put(desc->gdev);
 }
 
 /**
-- 
2.39.2