[PATCH 0/2] soc: amlogic: canvas: fix device leak on lookup

[PATCH 0/2] soc: amlogic: canvas: fix device leak on lookup

[Johan Hovold]

This series fixes a device leak in the canvas lookup helper and
simplifies the lookup error handling somewhat.

Johan


Johan Hovold (2):
  soc: amlogic: canvas: fix device leak on lookup
  soc: amlogic: canvas: simplify lookup error handling

 drivers/soc/amlogic/meson-canvas.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

-- 
2.49.1


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[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


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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

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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

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[PATCH 2/2] soc: amlogic: canvas: simplify lookup error handling

[Johan Hovold]

Simplify the canvas lookup error handling by dropping the OF node
reference sooner.

Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/soc/amlogic/meson-canvas.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/soc/amlogic/meson-canvas.c b/drivers/soc/amlogic/meson-canvas.c
index 0711088da5dc..79681afea8c6 100644
--- a/drivers/soc/amlogic/meson-canvas.c
+++ b/drivers/soc/amlogic/meson-canvas.c
@@ -60,12 +60,9 @@ struct meson_canvas *meson_canvas_get(struct device *dev)
 		return ERR_PTR(-ENODEV);
 
 	canvas_pdev = of_find_device_by_node(canvas_node);
-	if (!canvas_pdev) {
-		of_node_put(canvas_node);
-		return ERR_PTR(-EPROBE_DEFER);
-	}
-
 	of_node_put(canvas_node);
+	if (!canvas_pdev)
+		return ERR_PTR(-EPROBE_DEFER);
 
 	/*
 	 * If priv is NULL, it's probably because the canvas hasn't
-- 
2.49.1


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Re: [PATCH 2/2] soc: amlogic: canvas: simplify lookup error handling

[Markus Elfring]

> Simplify the canvas lookup error handling by dropping the OF node
> reference sooner.

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/of.h#L138

Regards,
Markus

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Re: [PATCH 2/2] soc: amlogic: canvas: simplify lookup error handling

[Martin Blumenstingl]

On Fri, Sep 26, 2025 at 4:25 PM Johan Hovold <johan@kernel.org> wrote:
>
> Simplify the canvas lookup error handling by dropping the OF node
> reference sooner.
>
> Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

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Re: [PATCH 0/2] soc: amlogic: canvas: fix device leak on lookup

[Neil Armstrong]

Hi,

On Fri, 26 Sep 2025 16:24:52 +0200, Johan Hovold wrote:
> This series fixes a device leak in the canvas lookup helper and
> simplifies the lookup error handling somewhat.
> 
> Johan
> 
> 
> Johan Hovold (2):
>   soc: amlogic: canvas: fix device leak on lookup
>   soc: amlogic: canvas: simplify lookup error handling
> 
> [...]

Thanks, Applied to https://git.kernel.org/pub/scm/linux/kernel/git/amlogic/linux.git (v6.19/drivers)

[1/2] soc: amlogic: canvas: fix device leak on lookup
      https://git.kernel.org/amlogic/c/32200f4828de9d7e6db379909898e718747f4e18
[2/2] soc: amlogic: canvas: simplify lookup error handling
      https://git.kernel.org/amlogic/c/075daf22641870e435a16ec2129bfd3b3134c487

These changes has been applied on the intermediate git tree [1].

The v6.19/drivers branch will then be sent via a formal Pull Request to the Linux SoC maintainers
for inclusion in their intermediate git branches in order to be sent to Linus during
the next merge window, or sooner if it's a set of fixes.

In the cases of fixes, those will be merged in the current release candidate
kernel and as soon they appear on the Linux master branch they will be
backported to the previous Stable and Long-Stable kernels [2].

The intermediate git branches are merged daily in the linux-next tree [3],
people are encouraged testing these pre-release kernels and report issues on the
relevant mailing-lists.

If problems are discovered on those changes, please submit a signed-off-by revert
patch followed by a corrective changeset.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/amlogic/linux.git
[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
[3] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

-- 
Neil


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