linux-kernel - [PATCH] chardev: fix consistent error handling in cdev_device

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Message-Id: <20251119101540.106441-1-zhangfei.gao@linaro.org>
Date: Wed, 19 Nov 2025 10:15:40 +0000
From: Zhangfei Gao <zhangfei.gao@...aro.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Wenkai Lin <linwenkai6@...ilicon.com>,
	Chenghai Huang <huangchenghai2@...wei.com>
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zhangfei Gao <zhangfei.gao@...aro.org>
Subject: [PATCH] chardev: fix consistent error handling in cdev_device_add

Currently cdev_device_add has inconsistent error handling:

- If device_add fails, it calls cdev_del(cdev)
- If cdev_add fails, it only returns error without cleanup

This creates a problem because cdev_set_parent(cdev, &dev->kobj)
establishes a parent-child relationship.
When callers use cdev_del(cdev) to clean up after cdev_add failure,
it also decrements the dev's refcount due to the parent relationship,
causing refcount mismatch.

To unify error handling:
- Set cdev->kobj.parent = NULL first to break the parent relationship
- Then call cdev_del(cdev) for cleanup

This ensures that in both error paths,
the dev's refcount remains consistent and callers don't need
special handling for different failure scenarios.

Signed-off-by: Zhangfei Gao <zhangfei.gao@...aro.org>
---
 fs/char_dev.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index c2ddb998f3c9..fef6ee1aba66 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -549,8 +549,11 @@ int cdev_device_add(struct cdev *cdev, struct device *dev)
 		cdev_set_parent(cdev, &dev->kobj);
 
 		rc = cdev_add(cdev, dev->devt, 1);
-		if (rc)
+		if (rc) {
+			cdev->kobj.parent = NULL;
+			cdev_del(cdev);
 			return rc;
+		}
 	}
 
 	rc = device_add(dev);
-- 
2.25.1