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Subject[PATCH v3] gpiolib: fix reference leaks when removing GPIO chips still in use
Date
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.org>
---
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
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