linux-kernel - [PATCH AUTOSEL 6.4 16/17] gpiolib: fix reference leaks when removing GPIO chips still in use

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Message-Id: <20230829133211.519957-16-sashal@kernel.org>
Date:   Tue, 29 Aug 2023 09:32:03 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sasha Levin <sashal@...nel.org>, brgl@...ev.pl,
        linux-gpio@...r.kernel.org
Subject: [PATCH AUTOSEL 6.4 16/17] gpiolib: fix reference leaks when removing GPIO chips still in use

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

[ Upstream commit 3386fb86ecdef0d39ee3306aea8ec290e61b934f ]

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>
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 5be8ad61523eb..6e7701f80929f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2175,12 +2175,18 @@ 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);
 }
 
 /**
-- 
2.40.1