linux-kernel - Re: [PATCH v2 RESEND] coresight: etm-perf: Fix reference count leak in etm_setup

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Message-ID: <20251219094141.GA9788@e132581.arm.com>
Date: Fri, 19 Dec 2025 09:41:41 +0000
From: Leo Yan <leo.yan@....com>
To: Ma Ke <make24@...as.ac.cn>
Cc: jie.gan@....qualcomm.com, james.clark@...aro.org,
	akpm@...ux-foundation.org, alexander.shishkin@...ux.intel.com,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org,
	mike.leach@...aro.org, stable@...r.kernel.org,
	suzuki.poulose@....com
Subject: Re: [PATCH v2 RESEND] coresight: etm-perf: Fix reference count leak
 in etm_setup_aux

Hi,

On Fri, Dec 19, 2025 at 10:39:49AM +0800, Ma Ke wrote:

[...]

> From the discussion, I note two possible fix directions:
> 
> 1. Release the initial reference in etm_setup_aux() (current v2 patch)
> 2. Modify the behavior of coresight_get_sink_by_id() itself so it 
> doesn't increase the reference count. 

The option 2 is the right way to go.

> To ensure the correctness of the v3 patch, I'd like to confirm which 
> patch is preferred. If option 2 is the consensus, I'm happy to modify 
> the implementation of coresight_get_sink_by_id() as suggested.

It is good to use a separate patch to fix
coresight_find_device_by_fwnode() mentioned by James:

diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
index 0db64c5f4995..2b34f818ba88 100644
--- a/drivers/hwtracing/coresight/coresight-platform.c
+++ b/drivers/hwtracing/coresight/coresight-platform.c
@@ -107,14 +107,16 @@ coresight_find_device_by_fwnode(struct fwnode_handle *fwnode)
 	 * platform bus.
 	 */
 	dev = bus_find_device_by_fwnode(&platform_bus_type, fwnode);
-	if (dev)
-		return dev;
 
 	/*
 	 * We have a configurable component - circle through the AMBA bus
 	 * looking for the device that matches the endpoint node.
 	 */
-	return bus_find_device_by_fwnode(&amba_bustype, fwnode);
+	if (!dev)
+		dev = bus_find_device_by_fwnode(&amba_bustype, fwnode);
+
+	put_device(dev);
+	return dev;
 }
 
 /*
@@ -274,7 +276,6 @@ static int of_coresight_parse_endpoint(struct device *dev,
 
 	of_node_put(rparent);
 	of_node_put(rep);
-	put_device(rdev);
 
 	return ret;
 }

Thanks for working on this.