[PATCH 1/2] soc: amlogic: canvas: fix device leak on lookup

[PATCH 1/2] soc: amlogic: canvas: fix device leak on lookup

[Johan Hovold]

Make sure to drop the reference taken to the canvas platform device when
looking up its driver data.

Note that holding a reference to a device does not prevent its driver
data from going away so there is no point in keeping the reference.

Also note that commit 28f851e6afa8 ("soc: amlogic: canvas: add missing
put_device() call in meson_canvas_get()") fixed the leak in a lookup
error path, but the reference is still leaking on success.

Fixes: d4983983d987 ("soc: amlogic: add meson-canvas driver")
Cc: stable@vger.kernel.org	# 4.20: 28f851e6afa8
Cc: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/soc/amlogic/meson-canvas.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/soc/amlogic/meson-canvas.c b/drivers/soc/amlogic/meson-canvas.c
index b6e06c4d2117..0711088da5dc 100644
--- a/drivers/soc/amlogic/meson-canvas.c
+++ b/drivers/soc/amlogic/meson-canvas.c
@@ -73,10 +73,9 @@ struct meson_canvas *meson_canvas_get(struct device *dev)
 	 * current state, this driver probe cannot return -EPROBE_DEFER
 	 */
 	canvas = dev_get_drvdata(&canvas_pdev->dev);
-	if (!canvas) {
-		put_device(&canvas_pdev->dev);
+	put_device(&canvas_pdev->dev);
+	if (!canvas)
 		return ERR_PTR(-EINVAL);
-	}
 
 	return canvas;
 }
-- 
2.49.1

Re: [PATCH 1/2] soc: amlogic: canvas: fix device leak on lookup

[Markus Elfring]

> Make sure to drop the reference taken to the canvas platform device when
> looking up its driver data.
…

How do you think about to increase the application of scope-based resource management?
https://elixir.bootlin.com/linux/v6.17-rc7/source/include/linux/device.h#L1180

Regards,
Markus

Re: [PATCH 1/2] soc: amlogic: canvas: fix device leak on lookup

[Martin Blumenstingl]

On Fri, Sep 26, 2025 at 4:25 PM Johan Hovold <johan@kernel.org> wrote:
>
> Make sure to drop the reference taken to the canvas platform device when
> looking up its driver data.
>
> Note that holding a reference to a device does not prevent its driver
> data from going away so there is no point in keeping the reference.
>
> Also note that commit 28f851e6afa8 ("soc: amlogic: canvas: add missing
> put_device() call in meson_canvas_get()") fixed the leak in a lookup
> error path, but the reference is still leaking on success.
>
> Fixes: d4983983d987 ("soc: amlogic: add meson-canvas driver")
> Cc: stable@vger.kernel.org      # 4.20: 28f851e6afa8
> Cc: Yu Kuai <yukuai3@huawei.com>
> Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

I haven't used the scope-based resource management myself as pointed
out by Markus.
That said, as far as I understand it's a feature in newer kernels and
this patch may be backported until 5.4 (oldest -stable kernel still
supported).
So let's go with this simple approach from Johan - we can still
improve this (without having to worry about backports).


Best regards,
Martin