linux-kernel - [PATCH] gpiolib: fix reference leaks when removing GPIO chips still in use

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Date:   Thu, 10 Aug 2023 12:03:34 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH] gpiolib: fix reference leaks when removing GPIO chips still in use

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

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@...aro.org>
---
I'm going through the resource management issues one-by-one using the
new virtual consumer module. This is something I found when I noticed
that IDA numbers never get freed for a chip that was removed with descs
still in use.

 drivers/gpio/gpiolib.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 251c875b5c34..7408e2561b2d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2167,12 +2167,14 @@ 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 {
+	if (!desc)
+		return;
+
+	if (!gpiod_free_commit(desc))
 		WARN_ON(extra_checks);
-	}
+
+	gpio_device_put(desc->gdev);
+	module_put(desc->gdev->owner);
 }
 
 /**
-- 
2.39.2