[PATH] drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram

[PATH] drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram

[yaolu]

From: Lu Yao <yaolu@kylinos.cn>

Need call 'pci_dev_put' after 'pci_get_domain_bus_and_slot'.

Signed-off-by: Lu Yao <yaolu@kylinos.cn>
---
 drivers/gpu/drm/loongson/lsdc_drv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/loongson/lsdc_drv.c b/drivers/gpu/drm/loongson/lsdc_drv.c
index 34405073c4d4..6cd21480c979 100644
--- a/drivers/gpu/drm/loongson/lsdc_drv.c
+++ b/drivers/gpu/drm/loongson/lsdc_drv.c
@@ -183,6 +183,7 @@ static int lsdc_get_dedicated_vram(struct lsdc_device *ldev,
 	ldev->vram_size = size;
 	ldev->gpu = pdev_gpu;
 
+	pci_dev_put(pdev_gpu);
 	drm_info(ddev, "Dedicated vram start: 0x%llx, size: %uMiB\n",
 		 (u64)base, (u32)(size >> 20));
 
-- 
2.25.1

Re: [PATH] drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram

[Markus Elfring]

> Need call 'pci_dev_put' after 'pci_get_domain_bus_and_slot'.

See also once more:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v7.1-rc4#n94

* How do you think about to add any tags (like “Fixes” and “Cc”) accordingly?

* Would it be helpful to append parentheses to function names?


https://elixir.bootlin.com/linux/v7.1-rc3/source/drivers/gpu/drm/loongson/lsdc_drv.c#L154-L190

Regards,
Markus

[PATCH v2] drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram()

[yaolu]

From: Lu Yao <yaolu@kylinos.cn>

Need to call pci_dev_put() after pci_get_domain_bus_and_slot().

Fixes: f39db26c5428 ("drm: Add kms driver for loongson display controller")
Signed-off-by: Lu Yao <yaolu@kylinos.cn>
---
v1->v2: add fixes tag and parentheses to function names suggested by
Markus.
  Link: https://lore.kernel.org/dri-devel/8ba844ab-9851-4045-a4e8-a96e6d1511e2@web.de/#R

 drivers/gpu/drm/loongson/lsdc_drv.c | 1 +
 1 file changed, 1 insertion(+)


diff --git a/drivers/gpu/drm/loongson/lsdc_drv.c b/drivers/gpu/drm/loongson/lsdc_drv.c
index 34405073c4d4..6cd21480c979 100644
--- a/drivers/gpu/drm/loongson/lsdc_drv.c
+++ b/drivers/gpu/drm/loongson/lsdc_drv.c
@@ -183,6 +183,7 @@ static int lsdc_get_dedicated_vram(struct lsdc_device *ldev,
 	ldev->vram_size = size;
 	ldev->gpu = pdev_gpu;
 
+	pci_dev_put(pdev_gpu);
 	drm_info(ddev, "Dedicated vram start: 0x%llx, size: %uMiB\n",
 		 (u64)base, (u32)(size >> 20));
 
-- 
2.25.1

Re: [PATCH v2] drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram()

[Markus Elfring]

> Need to call pci_dev_put() after pci_get_domain_bus_and_slot().

Can development interests occasionally grow also for further patch requirements?

* Usage of imperative mood

* Reference counting

* Completion of exception handling

* Related tags
  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/stable-kernel-rules.rst?h=v7.1-rc4#n34


Regards,
Markus

Re: [PATCH v2] drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram()

[Xi Ruoyao]

On Wed, 2026-05-20 at 09:47 +0800, yaolu@kylinos.cn wrote:
> From: Lu Yao <yaolu@kylinos.cn>
> 
> Need to call pci_dev_put() after pci_get_domain_bus_and_slot().
> 
> Fixes: f39db26c5428 ("drm: Add kms driver for loongson display controller")
> Signed-off-by: Lu Yao <yaolu@kylinos.cn>
> ---
> v1->v2: add fixes tag and parentheses to function names suggested by
> Markus.
>   Link: https://lore.kernel.org/dri-devel/8ba844ab-9851-4045-a4e8-a96e6d1511e2@web.de/#R
> 
>  drivers/gpu/drm/loongson/lsdc_drv.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> 
> diff --git a/drivers/gpu/drm/loongson/lsdc_drv.c b/drivers/gpu/drm/loongson/lsdc_drv.c
> index 34405073c4d4..6cd21480c979 100644
> --- a/drivers/gpu/drm/loongson/lsdc_drv.c
> +++ b/drivers/gpu/drm/loongson/lsdc_drv.c
> @@ -183,6 +183,7 @@ static int lsdc_get_dedicated_vram(struct lsdc_device *ldev,
>  	ldev->vram_size = size;
>  	ldev->gpu = pdev_gpu;
>  
> +	pci_dev_put(pdev_gpu);

It looks suspicious as pci_dev_put will immediately invalidate pdev_gpu
that we just assigned to ldev->gpu.

>From what I can tell it seems nobody is using that value though.  IMO we
should remove the assignment and also drop the gpu field in struct
lsdc_device.


-- 
Xi Ruoyao <xry111@xry111.site>

[PATCH v3] drm/loongson: rm unused member lsdc_device->gpu

[yaolu]

From: Lu Yao <yaolu@kylinos.cn>

lsdc_device->gpu never be used.
And there has a pci_dev refcount leak in lsdc_get_dedicated_vram() for
calling pci_get_domain_bus_and_slot().

Fixes: f39db26c5428 ("drm: Add kms driver for loongson display controller")
Signed-off-by: Lu Yao <yaolu@kylinos.cn>
---
v2->v3: rm lsdc_device->gpu for it don't be used suggested by Xi Ruoyao
  Link: https://lore.kernel.org/all/788292607f1d81531f27b6fb616debc2d0ec1da1.camel@xry111.site

v1->v2: add fixes tag and parentheses to function names suggested by
Markus.
  Link: https://lore.kernel.org/dri-devel/8ba844ab-9851-4045-a4e8-a96e6d1511e2@web.de

 drivers/gpu/drm/loongson/lsdc_drv.c | 2 +-
 drivers/gpu/drm/loongson/lsdc_drv.h | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/loongson/lsdc_drv.c b/drivers/gpu/drm/loongson/lsdc_drv.c
index 34405073c4d4..99b8f0cda7ad 100644
--- a/drivers/gpu/drm/loongson/lsdc_drv.c
+++ b/drivers/gpu/drm/loongson/lsdc_drv.c
@@ -181,8 +181,8 @@ static int lsdc_get_dedicated_vram(struct lsdc_device *ldev,
 
 	ldev->vram_base = base;
 	ldev->vram_size = size;
-	ldev->gpu = pdev_gpu;
 
+	pci_dev_put(pdev_gpu);
 	drm_info(ddev, "Dedicated vram start: 0x%llx, size: %uMiB\n",
 		 (u64)base, (u32)(size >> 20));
 
diff --git a/drivers/gpu/drm/loongson/lsdc_drv.h b/drivers/gpu/drm/loongson/lsdc_drv.h
index fbf2d760ef27..208bbcf689bf 100644
--- a/drivers/gpu/drm/loongson/lsdc_drv.h
+++ b/drivers/gpu/drm/loongson/lsdc_drv.h
@@ -269,7 +269,6 @@ struct lsdc_device {
 	/* @descp: features description of the DC variant */
 	const struct lsdc_desc *descp;
 	struct pci_dev *dc;
-	struct pci_dev *gpu;
 
 	struct loongson_gfxpll *gfxpll;
 
-- 
2.25.1

Re: [PATCH v3] drm/loongson: rm unused member lsdc_device->gpu

[Markus Elfring]

> lsdc_device->gpu never be used.
> And there has a pci_dev refcount leak in lsdc_get_dedicated_vram() for
> calling pci_get_domain_bus_and_slot().
Would there be a need to split adjustments into separate update steps?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v7.1-rc4#n81

Is the change description still improvable?

Regards,
Markus

Claude review: drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram()

[Claude Code Review Bot]

Overall Series Review

Subject: drm/loongson: fix pci_dev refcount leak in lsdc_get_dedicated_vram()
Author: yaolu@kylinos.cn
Patches: 5
Reviewed: 2026-05-25T21:54:00.145158

---

This mbox contains two versions of the same patch (v2 and v3) addressing a `pci_dev` refcount leak in the loongson display driver. The v3 patch is the latest and supersedes v2.

**v2** added a `pci_dev_put()` call but kept storing the reference in `ldev->gpu` — which would create a use-after-free risk (putting the reference while still holding a dangling pointer).

**v3** is the correct approach: it removes the unused `ldev->gpu` member entirely and drops the reference immediately after extracting the BAR resource information. This is clean and correct.

The fix is straightforward and addresses a real refcount leak. The `pci_get_domain_bus_and_slot()` function increments the refcount on the returned `pci_dev`, and without a corresponding `pci_dev_put()`, the device reference is leaked. Since the only information needed from `pdev_gpu` is the BAR base/size (extracted via `pci_resource_start`/`pci_resource_len`), there is no need to hold the reference long-term.

**Verdict:** v3 looks good to merge.

---
Generated by Claude Code Patch Reviewer