linux-kernel - [PATCH v2 2/5] drm/mediatek: Fix kobject put for component sub-drivers

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Message-ID: <20250403104741.71045-3-angelogioacchino.delregno@collabora.com>
Date: Thu,  3 Apr 2025 12:47:38 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: chunkuang.hu@...nel.org
Cc: p.zabel@...gutronix.de,
	airlied@...il.com,
	simona@...ll.ch,
	matthias.bgg@...il.com,
	angelogioacchino.delregno@...labora.com,
	nancy.lin@...iatek.com,
	ck.hu@...iatek.com,
	djkurtz@...omium.org,
	littlecvr@...omium.org,
	bibby.hsieh@...iatek.com,
	dri-devel@...ts.freedesktop.org,
	linux-mediatek@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	wenst@...omium.org,
	kernel@...labora.com
Subject: [PATCH v2 2/5] drm/mediatek: Fix kobject put for component sub-drivers

In function mtk_drm_get_all_drm_priv(), this driver is incrementing
the refcount for the sub-drivers of mediatek-drm with a call to
device_find_child() when taking a reference to all of those child
devices.

When the component bind fails multiple times this results in a
refcount_t overflow, as the reference count is never decremented:
fix that by adding a call to put_device() for all of the mmsys
devices in a loop, in error cases of mtk_drm_bind() and in the
mtk_drm_unbind() callback.

Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>
Link: https://lore.kernel.org/r/20250402083628.20111-3-angelogioacchino.delregno@collabora.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
---
 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index a8fbccb50c74..6b31df587507 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -676,6 +676,10 @@ static int mtk_drm_bind(struct device *dev)
 	for (i = 0; i < private->data->mmsys_dev_num; i++)
 		private->all_drm_private[i]->drm = NULL;
 err_put_dev:
+	for (i = 0; i < private->data->mmsys_dev_num; i++) {
+		/* For device_find_child in mtk_drm_get_all_priv() */
+		put_device(private->all_drm_private[i]->dev);
+	}
 	put_device(private->mutex_dev);
 	return ret;
 }
@@ -683,6 +687,7 @@ static int mtk_drm_bind(struct device *dev)
 static void mtk_drm_unbind(struct device *dev)
 {
 	struct mtk_drm_private *private = dev_get_drvdata(dev);
+	int i;
 
 	/* for multi mmsys dev, unregister drm dev in mmsys master */
 	if (private->drm_master) {
@@ -690,6 +695,10 @@ static void mtk_drm_unbind(struct device *dev)
 		mtk_drm_kms_deinit(private->drm);
 		drm_dev_put(private->drm);
 
+		for (i = 0; i < private->data->mmsys_dev_num; i++) {
+			/* For device_find_child in mtk_drm_get_all_priv() */
+			put_device(private->all_drm_private[i]->dev);
+		}
 		put_device(private->mutex_dev);
 	}
 	private->mtk_drm_bound = false;
-- 
2.48.1