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Message-ID: <51111c59-064f-1458-44ea-5fdae9f26211@arm.com>
Date:   Mon, 24 Apr 2023 11:43:11 +0100
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Subject: Re: [PATCH v5 13/13] coresight: Fix CTI module refcount leak by
 making it a helper device
Content-Language: en-US
To:     James Clark <james.clark@arm.com>, coresight@lists.linaro.org,
        quic_jinlmao@quicinc.com, mike.leach@linaro.org
Cc:     Mathieu Poirier <mathieu.poirier@linaro.org>,
        Leo Yan <leo.yan@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20230404155121.1824126-1-james.clark@arm.com>
 <20230404155121.1824126-14-james.clark@arm.com>
From:   Suzuki K Poulose <suzuki.poulose@arm.com>
In-Reply-To: <20230404155121.1824126-14-james.clark@arm.com>
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Precedence: bulk

On 04/04/2023 16:51, James Clark wrote:
> The CTI module has some hard coded refcounting code that has a leak.
> For example running perf and then trying to unload it fails:
> 
>    perf record -e cs_etm// -a -- ls
>    rmmod coresight_cti
> 
>    rmmod: ERROR: Module coresight_cti is in use
> 
> The coresight core already handles references of devices in use, so by
> making CTI a normal helper device, we get working refcounting for free.
> 
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-core.c  | 104 ++++++------------
>   .../hwtracing/coresight/coresight-cti-core.c  |  52 +++++----
>   .../hwtracing/coresight/coresight-cti-sysfs.c |   4 +-
>   drivers/hwtracing/coresight/coresight-cti.h   |   4 +-
>   drivers/hwtracing/coresight/coresight-priv.h  |   4 +-
>   drivers/hwtracing/coresight/coresight-sysfs.c |   4 +
>   include/linux/coresight.h                     |  30 +----
>   7 files changed, 75 insertions(+), 127 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 16689fe4ba98..2af416bba983 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -236,60 +236,44 @@ void coresight_disclaim_device(struct coresight_device *csdev)
>   }
>   EXPORT_SYMBOL_GPL(coresight_disclaim_device);
>   
> -/* enable or disable an associated CTI device of the supplied CS device */
> -static int
> -coresight_control_assoc_ectdev(struct coresight_device *csdev, bool enable)
> +/*
> + * Add a helper as an output device. This function takes the @coresight_mutex
> + * because it's assumed that it's called from the helper device, outside of the
> + * core code where the mutex would already be held. Don't add new calls to this
> + * from inside the core code, instead try to add the new helper to the DT and
> + * ACPI where it will be picked up and linked automatically.
> + */
> +void coresight_add_helper(struct coresight_device *csdev,
> +			  struct coresight_device *helper)
>   {
> -	int ect_ret = 0;
> -	struct coresight_device *ect_csdev = csdev->ect_dev;
> -	struct module *mod;
> +	int i;
> +	struct coresight_connection conn = {};
> +	struct coresight_connection *new_conn;
>   
> -	if (!ect_csdev)
> -		return 0;
> -	if ((!ect_ops(ect_csdev)->enable) || (!ect_ops(ect_csdev)->disable))
> -		return 0;
> +	mutex_lock(&coresight_mutex);
> +	conn.dest_fwnode = fwnode_handle_get(dev_fwnode(&helper->dev));
> +	conn.dest_dev = helper;
> +	conn.dest_port = conn.src_port = -1;
> +	conn.src_dev = csdev;
>   
> -	mod = ect_csdev->dev.parent->driver->owner;
> -	if (enable) {
> -		if (try_module_get(mod)) {
> -			ect_ret = ect_ops(ect_csdev)->enable(ect_csdev);
> -			if (ect_ret) {
> -				module_put(mod);
> -			} else {
> -				get_device(ect_csdev->dev.parent);
> -				csdev->ect_enabled = true;
> -			}
> -		} else
> -			ect_ret = -ENODEV;
> -	} else {
> -		if (csdev->ect_enabled) {
> -			ect_ret = ect_ops(ect_csdev)->disable(ect_csdev);
> -			put_device(ect_csdev->dev.parent);
> -			module_put(mod);
> -			csdev->ect_enabled = false;
> -		}
> -	}
> +	/*
> +	 * Check for duplicates because this is called every time a helper
> +	 * device is re-loaded. Existing connections will get re-linked
> +	 * automatically.
> +	 */
> +	for (i = 0; i < csdev->pdata->nr_outconns; ++i)
> +		if (csdev->pdata->out_conns[i]->dest_fwnode == conn.dest_fwnode)
> +			goto unlock;
>   
> -	/* output warning if ECT enable is preventing trace operation */
> -	if (ect_ret)
> -		dev_info(&csdev->dev, "Associated ECT device (%s) %s failed\n",
> -			 dev_name(&ect_csdev->dev),
> -			 enable ? "enable" : "disable");
> -	return ect_ret;
> -}
> +	new_conn =
> +		coresight_add_out_conn(csdev->dev.parent, csdev->pdata, &conn);

ultra minor nit:
	new_conn = coresight_add_out_conn(....,
					  .... );

> +	if (!IS_ERR(new_conn))
> +		coresight_add_in_conn(new_conn);
>   
> -/*
> - * Set the associated ect / cti device while holding the coresight_mutex
> - * to avoid a race with coresight_enable that may try to use this value.
> - */
> -void coresight_set_assoc_ectdev_mutex(struct coresight_device *csdev,
> -				      struct coresight_device *ect_csdev)
> -{
> -	mutex_lock(&coresight_mutex);
> -	csdev->ect_dev = ect_csdev;
> +unlock:
>   	mutex_unlock(&coresight_mutex);
>   }
> -EXPORT_SYMBOL_GPL(coresight_set_assoc_ectdev_mutex);
> +EXPORT_SYMBOL_GPL(coresight_add_helper);
>   
>   static int coresight_enable_sink(struct coresight_device *csdev,
>   				 enum cs_mode mode, void *data)
> @@ -303,12 +287,8 @@ static int coresight_enable_sink(struct coresight_device *csdev,
>   	if (!sink_ops(csdev)->enable)
>   		return -EINVAL;
>   
> -	ret = coresight_control_assoc_ectdev(csdev, true);
> -	if (ret)
> -		return ret;
>   	ret = sink_ops(csdev)->enable(csdev, mode, data);
>   	if (ret) {
> -		coresight_control_assoc_ectdev(csdev, false);
>   		return ret;
>   	}
>   	csdev->enable = true;
> @@ -326,7 +306,6 @@ static void coresight_disable_sink(struct coresight_device *csdev)
>   	ret = sink_ops(csdev)->disable(csdev);
>   	if (ret)
>   		return;
> -	coresight_control_assoc_ectdev(csdev, false);
>   	csdev->enable = false;
>   }
>   
> @@ -351,17 +330,11 @@ static int coresight_enable_link(struct coresight_device *csdev,
>   		return PTR_ERR(outconn);
>   
>   	if (link_ops(csdev)->enable) {
> -		ret = coresight_control_assoc_ectdev(csdev, true);
> -		if (!ret) {
> -			ret = link_ops(csdev)->enable(csdev, inconn, outconn);
> -			if (ret)
> -				coresight_control_assoc_ectdev(csdev, false);
> -		}
> +		ret = link_ops(csdev)->enable(csdev, inconn, outconn);
> +		if (!ret)
> +			csdev->enable = true;
>   	}
>   
> -	if (!ret)
> -		csdev->enable = true;
> -
>   	return ret;
>   }
>   
> @@ -382,7 +355,6 @@ static void coresight_disable_link(struct coresight_device *csdev,
>   
>   	if (link_ops(csdev)->disable) {
>   		link_ops(csdev)->disable(csdev, inconn, outconn);
> -		coresight_control_assoc_ectdev(csdev, false);
>   	}
>   
>   	if (link_subtype == CORESIGHT_DEV_SUBTYPE_LINK_MERG) {
> @@ -410,14 +382,9 @@ int coresight_enable_source(struct coresight_device *csdev, enum cs_mode mode,
>   
>   	if (!csdev->enable) {
>   		if (source_ops(csdev)->enable) {
> -			ret = coresight_control_assoc_ectdev(csdev, true);
> -			if (ret)
> -				return ret;
>   			ret = source_ops(csdev)->enable(csdev, data, mode);
> -			if (ret) {
> -				coresight_control_assoc_ectdev(csdev, false);
> +			if (ret)
>   				return ret;
> -			}
>   		}
>   		csdev->enable = true;
>   	}
> @@ -488,7 +455,6 @@ bool coresight_disable_source(struct coresight_device *csdev, void *data)
>   	if (atomic_dec_return(&csdev->refcnt) == 0) {
>   		if (source_ops(csdev)->disable)
>   			source_ops(csdev)->disable(csdev, data);
> -		coresight_control_assoc_ectdev(csdev, false);
>   		coresight_disable_helpers(csdev);
>   		csdev->enable = false;
>   	}

You may also remove the "ect" from the

static struct device_type coresight_dev_type[]

Suzuki