linux-kernel - [PATCH] cxl/region: Balance device refcount when destroying devices

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Message-Id: <20250714091654.3206432-1-make24@iscas.ac.cn>
Date: Mon, 14 Jul 2025 17:16:54 +0800
From: Ma Ke <make24@...as.ac.cn>
To: dave@...olabs.net,
	jonathan.cameron@...wei.com,
	dave.jiang@...el.com,
	alison.schofield@...el.com,
	vishal.l.verma@...el.com,
	ira.weiny@...el.com,
	dan.j.williams@...el.com,
	rrichter@....com,
	ming.li@...omail.com,
	zijun.hu@....qualcomm.com,
	fabio.m.de.francesco@...ux.intel.com
Cc: linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ma Ke <make24@...as.ac.cn>,
	stable@...r.kernel.org
Subject: [PATCH] cxl/region: Balance device refcount when destroying devices

Using device_find_child() to lookup the proper device to destroy
causes an unbalance in device refcount, since device_find_child()
calls an implicit get_device() to increment the device's reference
count before returning the pointer. cxl_port_find_switch_decoder()
directly converts this pointer to a cxl_decoder and returns it without
releasing the reference properly. We should call put_device() to
decrement reference count.

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: d6879d8cfb81 ("cxl/region: Add function to find a port's switch decoder by range")
Signed-off-by: Ma Ke <make24@...as.ac.cn>
---
 drivers/cxl/core/region.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 6e5e1460068d..cae16d761261 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -3234,6 +3234,9 @@ cxl_port_find_switch_decoder(struct cxl_port *port, struct range *hpa)
 	struct device *cxld_dev = device_find_child(&port->dev, hpa,
 						    match_decoder_by_range);
 
+	/* Drop the refcnt bumped implicitly by device_find_child */
+	put_device(cxld_dev);
+
 	return cxld_dev ? to_cxl_decoder(cxld_dev) : NULL;
 }
 
-- 
2.25.1