linux-kernel - [PATCH] sunvdc: Balance device refcount in vdc_port_mpgroup

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Message-Id: <20250718082236.3400483-1-make24@iscas.ac.cn>
Date: Fri, 18 Jul 2025 16:22:36 +0800
From: Ma Ke <make24@...as.ac.cn>
To: axboe@...nel.dk,
	sln@...main.com,
	Jim.Quigley@...cle.com,
	liam.merwick@...cle.com,
	aaron.young@...cle.com,
	alexandre.chartre@...cle.com
Cc: akpm@...ux-foundation.org,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ma Ke <make24@...as.ac.cn>,
	stable@...r.kernel.org
Subject: [PATCH] sunvdc: Balance device refcount in vdc_port_mpgroup_check

Using device_find_child() to locate a probed virtual-device-port node
causes a device refcount imbalance, as device_find_child() internally
calls get_device() to increment the device’s reference count before
returning its pointer. vdc_port_mpgroup_check() directly returns true
upon finding a matching device without releasing the reference via
put_device(). We should call put_device() to decrement refcount.

As comment of device_find_child() says, 'NOTE: you will need to drop
the reference with put_device() after use'.

Found by code review.

Cc: stable@...r.kernel.org
Fixes: 3ee70591d6c4 ("sunvdc: prevent sunvdc panic when mpgroup disk added to guest domain")
Signed-off-by: Ma Ke <make24@...as.ac.cn>
---
 drivers/block/sunvdc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/block/sunvdc.c b/drivers/block/sunvdc.c
index b5727dea15bd..b6dbd5dd2723 100644
--- a/drivers/block/sunvdc.c
+++ b/drivers/block/sunvdc.c
@@ -950,6 +950,7 @@ static bool vdc_port_mpgroup_check(struct vio_dev *vdev)
 {
 	struct vdc_check_port_data port_data;
 	struct device *dev;
+	bool found = false;
 
 	port_data.dev_no = vdev->dev_no;
 	port_data.type = (char *)&vdev->type;
@@ -957,10 +958,12 @@ static bool vdc_port_mpgroup_check(struct vio_dev *vdev)
 	dev = device_find_child(vdev->dev.parent, &port_data,
 				vdc_device_probed);
 
-	if (dev)
-		return true;
+	if (dev) {
+		found = true;
+		put_device(dev);
+	}
 
-	return false;
+	return found;
 }
 
 static int vdc_port_probe(struct vio_dev *vdev, const struct vio_device_id *id)
-- 
2.25.1