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

From: Tingwei Zhang <tingweiz@codeaurora•org>
To: Mathieu Poirier <mathieu.poirier@linaro•org>
Cc: tsoni@codeaurora•org,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora•org>,
	Kim Phillips <kim.phillips@arm•com>,
	Mao Jinlong <jinlmao@codeaurora•org>,
	Suzuki K Poulose <suzuki.poulose@arm•com>,
	Alexander Shishkin <alexander.shishkin@linux•intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
	coresight@lists•linaro.org, Randy Dunlap <rdunlap@infradead•org>,
	Mian Yousaf Kaukab <ykaukab@suse•de>,
	Russell King <linux@armlinux•org.uk>,
	Tingwei Zhang <tingwei@codeaurora•org>,
	Leo Yan <leo.yan@linaro•org>,
	linux-arm-kernel@lists•infradead.org,
	Mike Leach <mike.leach@linaro•org>
Subject: Re: [PATCH v8 06/24] coresight: add try_get_module() in coresight_grab_device()
Date: Thu, 13 Aug 2020 15:37:20 +0800	[thread overview]
Message-ID: <20200813073720.GA10706@codeaurora.org> (raw)
In-Reply-To: <20200812193612.GE3393195@xps15>

On Thu, Aug 13, 2020 at 03:36:12AM +0800, Mathieu Poirier wrote:
> 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.
> 
Agree. I'll fix in next revision.

Thanks,
Tingwei

> 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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