Re: [PATCH v8 06/24] coresight: add try_get_module() in coresight_grab_device()

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Fri, Aug 07, 2020 at 07:11:35PM +0800, Tingwei Zhang wrote:
> When coresight device is in an active session, driver module of
> that device should not be removed. Use try_get_module() in
> coresight_grab_device() to prevent module to be unloaded.
> Use get_device()/put_device() to protect device data
> in the middle of active session.
> 
> Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>
> Tested-by: Mike Leach <mike.leach@linaro.org>
> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>  drivers/hwtracing/coresight/coresight.c | 61 ++++++++++++++++++++++---
>  1 file changed, 54 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index b7151c5f81b1..0b0e31577b9b 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -634,13 +634,45 @@ struct coresight_device *coresight_get_sink_by_id(u32 id)
>  	return dev ? to_coresight_device(dev) : NULL;
>  }
>  
> +/**
> + * coresight_get_ref- Helper function to increase reference count to module
> + * and device.
> + * Return true in successful case and power up the device.
> + * Return false when failed to get reference of module.
> + */
> +static inline bool coresight_get_ref(struct coresight_device *csdev)
> +{
> +	struct device *dev = csdev->dev.parent;
> +
> +	/* Make sure the driver can't be removed */
> +	if (!try_module_get(dev->driver->owner))
> +		return false;
> +	/* Make sure the device can't go away */
> +	get_device(dev);
> +	pm_runtime_get_sync(dev);
> +	return true;
> +}
> +
> +/**
> + * coresight_put_ref- Helper function to decrease reference count to module
> + * and device. Power off the device.
> + */
> +static inline void coresight_put_ref(struct coresight_device *csdev)
> +{
> +	struct device *dev = csdev->dev.parent;
> +
> +	pm_runtime_put(dev);
> +	put_device(dev);
> +	module_put(dev->driver->owner);
> +}
> +
>  /*
>   * coresight_grab_device - Power up this device and any of the helper
>   * devices connected to it for trace operation. Since the helper devices
>   * don't appear on the trace path, they should be handled along with the
>   * the master device.
>   */
> -static void coresight_grab_device(struct coresight_device *csdev)
> +static int coresight_grab_device(struct coresight_device *csdev)
>  {
>  	int i;
>  
> @@ -649,9 +681,20 @@ static void coresight_grab_device(struct coresight_device *csdev)
>  
>  		child  = csdev->pdata->conns[i].child_dev;
>  		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
> -			pm_runtime_get_sync(child->dev.parent);
> +			if (!coresight_get_ref(child))
> +				goto err;
> +	}
> +	if (coresight_get_ref(csdev))
> +		return 0;
> +err:
> +	for (i--; i >= 0; i--) {
> +		struct coresight_device *child;
> +
> +		child  = csdev->pdata->conns[i].child_dev;
> +		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
> +			coresight_put_ref(child);
>  	}
> -	pm_runtime_get_sync(csdev->dev.parent);
> +	return -ENODEV;
>  }
>  
>  /*
> @@ -662,13 +705,13 @@ static void coresight_drop_device(struct coresight_device *csdev)
>  {
>  	int i;
>  
> -	pm_runtime_put(csdev->dev.parent);
> +	coresight_put_ref(csdev);
>  	for (i = 0; i < csdev->pdata->nr_outport; i++) {
>  		struct coresight_device *child;
>  
>  		child  = csdev->pdata->conns[i].child_dev;
>  		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
> -			pm_runtime_put(child->dev.parent);
> +			coresight_put_ref(child);
>  	}
>  }
>  
> @@ -687,7 +730,7 @@ static int _coresight_build_path(struct coresight_device *csdev,
>  				 struct coresight_device *sink,
>  				 struct list_head *path)
>  {
> -	int i;
> +	int i, ret;
>  	bool found = false;
>  	struct coresight_node *node;
>  
> @@ -721,7 +764,11 @@ static int _coresight_build_path(struct coresight_device *csdev,
>  	if (!node)
>  		return -ENOMEM;
>  
> -	coresight_grab_device(csdev);
> +	ret = coresight_grab_device(csdev);

I suggest trying to grab the device before allocating memory for the node.  If
grabing the device fails memory doesn't have to be allocated and released
needlessly.

I will likely come back to this patch later after reviewing the rest the this
set.

Thanks,
Mathieu

> +	if (ret) {
> +		kfree(node);
> +		return ret;
> +	}
>  	node->csdev = csdev;
>  	list_add(&node->link, path);
>  
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 

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