[PATCH v2 0/1] rpmsg: ctrl: Add ability to instantiate rpmsg device locally

[PATCH v2 0/1] rpmsg: ctrl: Add ability to instantiate rpmsg device locally

[Arnaud Pouliquen]

Purpose:
  Allow the user space application to create and release an rpmsg device by adding
  rpmsg ioctrl to the /dev/rpmsg_ctrl interface
    
Aim:
  The current implementation is based on the enumeration of services by the 
  remote processor to create a new channel and instantiate associated rpmsg device.
  There is no solution to create a rpmsg channel on user application request.
  If the rpmsg char driver allows adding a new endpoint over an existing channel, it
  does not offer the ability to create a new one.
  Adding the IOCTRL to instantiate rpmsg channels from the user application will allow
  to dynamically create and destroy rpmsg devices. Some examples of use are:
  - activate the service at the initiative of the application,
  - remove the communication on a specific channel before entering the suspend mode,
  - creating a temporary channel for debugging purposes.


Delta vs V1 [1]
- Squah patches 1/4(rpmsg: ctrl: Introduce RPMSG_CREATE_DEV_IOCTL) and
  2/4 (rpmsg: ctrl: Introduce RPMSG_RELEASE_DEV_IOCTL).
- Remove the rpmsg device attribue to check if a rpmg device can be released, choose to trust
  the application (a similar trust already exists for the bind/unbind interface).

[1] https://patchwork.kernel.org/project/linux-remoteproc/list/?series=494021

How to test it:
  - This series can be applied on git/andersson/remoteproc.git for-next branch (dc0e14fa833b)
    + the "Restructure the rpmsg char to decorrelate the control part" series[2]
  - to test the ioctrl, a rpmsgexportdev tool is available here:
     https://github.com/arnopo/rpmsgexport

[2]https://patchwork.kernel.org/project/linux-remoteproc/list/?series=483793

Arnaud Pouliquen (1):
  rpmsg: ctrl: Introduce new RPMSG_CREATE/RELEASE_DEV_IOCTL controls

 drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++++++----
 include/uapi/linux/rpmsg.h | 10 ++++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)

-- 
2.17.1

[PATCH v2 1/1] rpmsg: ctrl: Introduce new RPMSG_CREATE/RELEASE_DEV_IOCTL controls

[Arnaud Pouliquen]

Allow the user space application to create and release an rpmsg device
by adding RPMSG_CREATE_DEV_IOCTL and RPMSG_RELEASE_DEV_IOCTL ioctrls to
the /dev/rpmsg_ctrl interface

The RPMSG_CREATE_DEV_IOCTL Ioctl can be used to instantiate a local rpmsg
device.
Depending on the back-end implementation, the associated rpmsg driver is
probed and a NS announcement can be sent to the remote processor.

The RPMSG_RELEASE_DEV_IOCTL allows the user application to release a
rpmsg device created either by the remote processor or with the
RPMSG_CREATE_DEV_IOCTL call.
Depending on the back-end implementation, the associated rpmsg driver is
removed and a NS destroy rpmsg can be sent to the remote processor.

Suggested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
---
 drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++++++----
 include/uapi/linux/rpmsg.h | 10 ++++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
index eeb1708548c1..cb19e32d05e1 100644
--- a/drivers/rpmsg/rpmsg_ctrl.c
+++ b/drivers/rpmsg/rpmsg_ctrl.c
@@ -23,6 +23,7 @@
 #include <uapi/linux/rpmsg.h>
 
 #include "rpmsg_char.h"
+#include "rpmsg_internal.h"
 
 static dev_t rpmsg_major;
 
@@ -37,11 +38,13 @@ static DEFINE_IDA(rpmsg_minor_ida);
  * @rpdev:	underlaying rpmsg device
  * @cdev:	cdev for the ctrl device
  * @dev:	device for the ctrl device
+ * @ctrl_lock:	serialize the ioctrls.
  */
 struct rpmsg_ctrldev {
 	struct rpmsg_device *rpdev;
 	struct cdev cdev;
 	struct device dev;
+	struct mutex ctrl_lock;
 };
 
 static int rpmsg_ctrldev_open(struct inode *inode, struct file *filp)
@@ -70,9 +73,8 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
 	void __user *argp = (void __user *)arg;
 	struct rpmsg_endpoint_info eptinfo;
 	struct rpmsg_channel_info chinfo;
-
-	if (cmd != RPMSG_CREATE_EPT_IOCTL)
-		return -EINVAL;
+	struct rpmsg_device *rpdev;
+	int ret = 0;
 
 	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
 		return -EFAULT;
@@ -82,7 +84,33 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
 	chinfo.src = eptinfo.src;
 	chinfo.dst = eptinfo.dst;
 
-	return rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
+	mutex_lock(&ctrldev->ctrl_lock);
+	switch (cmd) {
+	case RPMSG_CREATE_EPT_IOCTL:
+		ret = rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
+		break;
+
+	case RPMSG_CREATE_DEV_IOCTL:
+		rpdev = rpmsg_create_channel(ctrldev->rpdev, &chinfo);
+		if (!rpdev) {
+			dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name);
+			ret = -ENXIO;
+		}
+		break;
+
+	case RPMSG_RELEASE_DEV_IOCTL:
+		ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo);
+		if (ret)
+			dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n",
+				chinfo.name, ret);
+		break;
+
+	default:
+		ret = -EINVAL;
+	}
+	mutex_unlock(&ctrldev->ctrl_lock);
+
+	return ret;
 };
 
 static const struct file_operations rpmsg_ctrldev_fops = {
@@ -119,6 +147,7 @@ static int rpmsg_ctrldev_probe(struct rpmsg_device *rpdev)
 	device_initialize(dev);
 	dev->parent = &rpdev->dev;
 
+	mutex_init(&ctrldev->ctrl_lock);
 	cdev_init(&ctrldev->cdev, &rpmsg_ctrldev_fops);
 	ctrldev->cdev.owner = THIS_MODULE;
 
diff --git a/include/uapi/linux/rpmsg.h b/include/uapi/linux/rpmsg.h
index f5ca8740f3fb..1637e68177d9 100644
--- a/include/uapi/linux/rpmsg.h
+++ b/include/uapi/linux/rpmsg.h
@@ -33,4 +33,14 @@ struct rpmsg_endpoint_info {
  */
 #define RPMSG_DESTROY_EPT_IOCTL	_IO(0xb5, 0x2)
 
+/**
+ * Instantiate a new local rpmsg service device.
+ */
+#define RPMSG_CREATE_DEV_IOCTL	_IOW(0xb5, 0x3, struct rpmsg_endpoint_info)
+
+/**
+ * Release a local rpmsg device.
+ */
+#define RPMSG_RELEASE_DEV_IOCTL	_IOW(0xb5, 0x4, struct rpmsg_endpoint_info)
+
 #endif
-- 
2.17.1

Re: [PATCH v2 1/1] rpmsg: ctrl: Introduce new RPMSG_CREATE/RELEASE_DEV_IOCTL controls

[Mathieu Poirier]

On Mon, Jun 21, 2021 at 02:58:00PM +0200, Arnaud Pouliquen wrote:
> Allow the user space application to create and release an rpmsg device
> by adding RPMSG_CREATE_DEV_IOCTL and RPMSG_RELEASE_DEV_IOCTL ioctrls to
> the /dev/rpmsg_ctrl interface
> 
> The RPMSG_CREATE_DEV_IOCTL Ioctl can be used to instantiate a local rpmsg
> device.
> Depending on the back-end implementation, the associated rpmsg driver is
> probed and a NS announcement can be sent to the remote processor.
> 
> The RPMSG_RELEASE_DEV_IOCTL allows the user application to release a
> rpmsg device created either by the remote processor or with the
> RPMSG_CREATE_DEV_IOCTL call.
> Depending on the back-end implementation, the associated rpmsg driver is
> removed and a NS destroy rpmsg can be sent to the remote processor.
> 
> Suggested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
> ---
>  drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++++++----
>  include/uapi/linux/rpmsg.h | 10 ++++++++++
>  2 files changed, 43 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
> index eeb1708548c1..cb19e32d05e1 100644
> --- a/drivers/rpmsg/rpmsg_ctrl.c
> +++ b/drivers/rpmsg/rpmsg_ctrl.c
> @@ -23,6 +23,7 @@
>  #include <uapi/linux/rpmsg.h>
>  
>  #include "rpmsg_char.h"
> +#include "rpmsg_internal.h"
>  
>  static dev_t rpmsg_major;
>  
> @@ -37,11 +38,13 @@ static DEFINE_IDA(rpmsg_minor_ida);
>   * @rpdev:	underlaying rpmsg device
>   * @cdev:	cdev for the ctrl device
>   * @dev:	device for the ctrl device
> + * @ctrl_lock:	serialize the ioctrls.
>   */
>  struct rpmsg_ctrldev {
>  	struct rpmsg_device *rpdev;
>  	struct cdev cdev;
>  	struct device dev;
> +	struct mutex ctrl_lock;
>  };
>  
>  static int rpmsg_ctrldev_open(struct inode *inode, struct file *filp)
> @@ -70,9 +73,8 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
>  	void __user *argp = (void __user *)arg;
>  	struct rpmsg_endpoint_info eptinfo;
>  	struct rpmsg_channel_info chinfo;
> -
> -	if (cmd != RPMSG_CREATE_EPT_IOCTL)
> -		return -EINVAL;
> +	struct rpmsg_device *rpdev;
> +	int ret = 0;
>  
>  	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
>  		return -EFAULT;
> @@ -82,7 +84,33 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
>  	chinfo.src = eptinfo.src;
>  	chinfo.dst = eptinfo.dst;
>  
> -	return rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
> +	mutex_lock(&ctrldev->ctrl_lock);

Have you been able to verify the VFS layer doesn't take care of serializing
ioctl() and file accesses in general?  I did a quick search in the drivers/
directory and the vast majority of implementations don't use a lock.

Thanks,
Mathieu

> +	switch (cmd) {
> +	case RPMSG_CREATE_EPT_IOCTL:
> +		ret = rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
> +		break;
> +
> +	case RPMSG_CREATE_DEV_IOCTL:
> +		rpdev = rpmsg_create_channel(ctrldev->rpdev, &chinfo);
> +		if (!rpdev) {
> +			dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name);
> +			ret = -ENXIO;
> +		}
> +		break;
> +
> +	case RPMSG_RELEASE_DEV_IOCTL:
> +		ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo);
> +		if (ret)
> +			dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n",
> +				chinfo.name, ret);
> +		break;
> +
> +	default:
> +		ret = -EINVAL;
> +	}
> +	mutex_unlock(&ctrldev->ctrl_lock);
> +
> +	return ret;
>  };
>  
>  static const struct file_operations rpmsg_ctrldev_fops = {
> @@ -119,6 +147,7 @@ static int rpmsg_ctrldev_probe(struct rpmsg_device *rpdev)
>  	device_initialize(dev);
>  	dev->parent = &rpdev->dev;
>  
> +	mutex_init(&ctrldev->ctrl_lock);
>  	cdev_init(&ctrldev->cdev, &rpmsg_ctrldev_fops);
>  	ctrldev->cdev.owner = THIS_MODULE;
>  
> diff --git a/include/uapi/linux/rpmsg.h b/include/uapi/linux/rpmsg.h
> index f5ca8740f3fb..1637e68177d9 100644
> --- a/include/uapi/linux/rpmsg.h
> +++ b/include/uapi/linux/rpmsg.h
> @@ -33,4 +33,14 @@ struct rpmsg_endpoint_info {
>   */
>  #define RPMSG_DESTROY_EPT_IOCTL	_IO(0xb5, 0x2)
>  
> +/**
> + * Instantiate a new local rpmsg service device.
> + */
> +#define RPMSG_CREATE_DEV_IOCTL	_IOW(0xb5, 0x3, struct rpmsg_endpoint_info)
> +
> +/**
> + * Release a local rpmsg device.
> + */
> +#define RPMSG_RELEASE_DEV_IOCTL	_IOW(0xb5, 0x4, struct rpmsg_endpoint_info)
> +
>  #endif
> -- 
> 2.17.1
> 

Re: [PATCH v2 1/1] rpmsg: ctrl: Introduce new RPMSG_CREATE/RELEASE_DEV_IOCTL controls

[Arnaud POULIQUEN]

Hi Mathieu

On 6/22/21 1:16 AM, Mathieu Poirier wrote:
> On Mon, Jun 21, 2021 at 02:58:00PM +0200, Arnaud Pouliquen wrote:
>> Allow the user space application to create and release an rpmsg device
>> by adding RPMSG_CREATE_DEV_IOCTL and RPMSG_RELEASE_DEV_IOCTL ioctrls to
>> the /dev/rpmsg_ctrl interface
>>
>> The RPMSG_CREATE_DEV_IOCTL Ioctl can be used to instantiate a local rpmsg
>> device.
>> Depending on the back-end implementation, the associated rpmsg driver is
>> probed and a NS announcement can be sent to the remote processor.
>>
>> The RPMSG_RELEASE_DEV_IOCTL allows the user application to release a
>> rpmsg device created either by the remote processor or with the
>> RPMSG_CREATE_DEV_IOCTL call.
>> Depending on the back-end implementation, the associated rpmsg driver is
>> removed and a NS destroy rpmsg can be sent to the remote processor.
>>
>> Suggested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
>> ---
>>  drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++++++----
>>  include/uapi/linux/rpmsg.h | 10 ++++++++++
>>  2 files changed, 43 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
>> index eeb1708548c1..cb19e32d05e1 100644
>> --- a/drivers/rpmsg/rpmsg_ctrl.c
>> +++ b/drivers/rpmsg/rpmsg_ctrl.c
>> @@ -23,6 +23,7 @@
>>  #include <uapi/linux/rpmsg.h>
>>  
>>  #include "rpmsg_char.h"
>> +#include "rpmsg_internal.h"
>>  
>>  static dev_t rpmsg_major;
>>  
>> @@ -37,11 +38,13 @@ static DEFINE_IDA(rpmsg_minor_ida);
>>   * @rpdev:	underlaying rpmsg device
>>   * @cdev:	cdev for the ctrl device
>>   * @dev:	device for the ctrl device
>> + * @ctrl_lock:	serialize the ioctrls.
>>   */
>>  struct rpmsg_ctrldev {
>>  	struct rpmsg_device *rpdev;
>>  	struct cdev cdev;
>>  	struct device dev;
>> +	struct mutex ctrl_lock;
>>  };
>>  
>>  static int rpmsg_ctrldev_open(struct inode *inode, struct file *filp)
>> @@ -70,9 +73,8 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
>>  	void __user *argp = (void __user *)arg;
>>  	struct rpmsg_endpoint_info eptinfo;
>>  	struct rpmsg_channel_info chinfo;
>> -
>> -	if (cmd != RPMSG_CREATE_EPT_IOCTL)
>> -		return -EINVAL;
>> +	struct rpmsg_device *rpdev;
>> +	int ret = 0;
>>  
>>  	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
>>  		return -EFAULT;
>> @@ -82,7 +84,33 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
>>  	chinfo.src = eptinfo.src;
>>  	chinfo.dst = eptinfo.dst;
>>  
>> -	return rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
>> +	mutex_lock(&ctrldev->ctrl_lock);
> 
> Have you been able to verify the VFS layer doesn't take care of serializing
> ioctl() and file accesses in general?  I did a quick search in the drivers/
> directory and the vast majority of implementations don't use a lock.

Please find my answer here https://lkml.org/lkml/2021/6/21/235
I tested by suppressing the lock and adding msleep to check a potential atomic.
in the rpmsg_ctrldev_ioctl function. Nothing seems prevent the re-entrance.

Regards,
Arnaud

> 
> Thanks,
> Mathieu
> 
>> +	switch (cmd) {
>> +	case RPMSG_CREATE_EPT_IOCTL:
>> +		ret = rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
>> +		break;
>> +
>> +	case RPMSG_CREATE_DEV_IOCTL:
>> +		rpdev = rpmsg_create_channel(ctrldev->rpdev, &chinfo);
>> +		if (!rpdev) {
>> +			dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name);
>> +			ret = -ENXIO;
>> +		}
>> +		break;
>> +
>> +	case RPMSG_RELEASE_DEV_IOCTL:
>> +		ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo);
>> +		if (ret)
>> +			dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n",
>> +				chinfo.name, ret);
>> +		break;
>> +
>> +	default:
>> +		ret = -EINVAL;
>> +	}
>> +	mutex_unlock(&ctrldev->ctrl_lock);
>> +
>> +	return ret;
>>  };
>>  
>>  static const struct file_operations rpmsg_ctrldev_fops = {
>> @@ -119,6 +147,7 @@ static int rpmsg_ctrldev_probe(struct rpmsg_device *rpdev)
>>  	device_initialize(dev);
>>  	dev->parent = &rpdev->dev;
>>  
>> +	mutex_init(&ctrldev->ctrl_lock);
>>  	cdev_init(&ctrldev->cdev, &rpmsg_ctrldev_fops);
>>  	ctrldev->cdev.owner = THIS_MODULE;
>>  
>> diff --git a/include/uapi/linux/rpmsg.h b/include/uapi/linux/rpmsg.h
>> index f5ca8740f3fb..1637e68177d9 100644
>> --- a/include/uapi/linux/rpmsg.h
>> +++ b/include/uapi/linux/rpmsg.h
>> @@ -33,4 +33,14 @@ struct rpmsg_endpoint_info {
>>   */
>>  #define RPMSG_DESTROY_EPT_IOCTL	_IO(0xb5, 0x2)
>>  
>> +/**
>> + * Instantiate a new local rpmsg service device.
>> + */
>> +#define RPMSG_CREATE_DEV_IOCTL	_IOW(0xb5, 0x3, struct rpmsg_endpoint_info)
>> +
>> +/**
>> + * Release a local rpmsg device.
>> + */
>> +#define RPMSG_RELEASE_DEV_IOCTL	_IOW(0xb5, 0x4, struct rpmsg_endpoint_info)
>> +
>>  #endif
>> -- 
>> 2.17.1
>>

Re: [PATCH v2 1/1] rpmsg: ctrl: Introduce new RPMSG_CREATE/RELEASE_DEV_IOCTL controls

[Mathieu Poirier]

On Tue, Jun 22, 2021 at 09:43:49AM +0200, Arnaud POULIQUEN wrote:
> Hi Mathieu
> 
> On 6/22/21 1:16 AM, Mathieu Poirier wrote:
> > On Mon, Jun 21, 2021 at 02:58:00PM +0200, Arnaud Pouliquen wrote:
> >> Allow the user space application to create and release an rpmsg device
> >> by adding RPMSG_CREATE_DEV_IOCTL and RPMSG_RELEASE_DEV_IOCTL ioctrls to
> >> the /dev/rpmsg_ctrl interface
> >>
> >> The RPMSG_CREATE_DEV_IOCTL Ioctl can be used to instantiate a local rpmsg
> >> device.
> >> Depending on the back-end implementation, the associated rpmsg driver is
> >> probed and a NS announcement can be sent to the remote processor.
> >>
> >> The RPMSG_RELEASE_DEV_IOCTL allows the user application to release a
> >> rpmsg device created either by the remote processor or with the
> >> RPMSG_CREATE_DEV_IOCTL call.
> >> Depending on the back-end implementation, the associated rpmsg driver is
> >> removed and a NS destroy rpmsg can be sent to the remote processor.
> >>
> >> Suggested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> >> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
> >> ---
> >>  drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++++++----
> >>  include/uapi/linux/rpmsg.h | 10 ++++++++++
> >>  2 files changed, 43 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
> >> index eeb1708548c1..cb19e32d05e1 100644
> >> --- a/drivers/rpmsg/rpmsg_ctrl.c
> >> +++ b/drivers/rpmsg/rpmsg_ctrl.c
> >> @@ -23,6 +23,7 @@
> >>  #include <uapi/linux/rpmsg.h>
> >>  
> >>  #include "rpmsg_char.h"
> >> +#include "rpmsg_internal.h"
> >>  
> >>  static dev_t rpmsg_major;
> >>  
> >> @@ -37,11 +38,13 @@ static DEFINE_IDA(rpmsg_minor_ida);
> >>   * @rpdev:	underlaying rpmsg device
> >>   * @cdev:	cdev for the ctrl device
> >>   * @dev:	device for the ctrl device
> >> + * @ctrl_lock:	serialize the ioctrls.
> >>   */
> >>  struct rpmsg_ctrldev {
> >>  	struct rpmsg_device *rpdev;
> >>  	struct cdev cdev;
> >>  	struct device dev;
> >> +	struct mutex ctrl_lock;
> >>  };
> >>  
> >>  static int rpmsg_ctrldev_open(struct inode *inode, struct file *filp)
> >> @@ -70,9 +73,8 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
> >>  	void __user *argp = (void __user *)arg;
> >>  	struct rpmsg_endpoint_info eptinfo;
> >>  	struct rpmsg_channel_info chinfo;
> >> -
> >> -	if (cmd != RPMSG_CREATE_EPT_IOCTL)
> >> -		return -EINVAL;
> >> +	struct rpmsg_device *rpdev;
> >> +	int ret = 0;
> >>  
> >>  	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
> >>  		return -EFAULT;
> >> @@ -82,7 +84,33 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
> >>  	chinfo.src = eptinfo.src;
> >>  	chinfo.dst = eptinfo.dst;
> >>  
> >> -	return rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
> >> +	mutex_lock(&ctrldev->ctrl_lock);
> > 
> > Have you been able to verify the VFS layer doesn't take care of serializing
> > ioctl() and file accesses in general?  I did a quick search in the drivers/
> > directory and the vast majority of implementations don't use a lock.
> 
> Please find my answer here https://lkml.org/lkml/2021/6/21/235

Ah ok, I hadn't noticed that one.

> I tested by suppressing the lock and adding msleep to check a potential atomic.
> in the rpmsg_ctrldev_ioctl function. Nothing seems prevent the re-entrance.

Thanks for testing this out.  I did some research on my side and turns out
unlocked_ioctl() was introduced to get rid of the Big Kernel Lock rather than
indicate that serialisation is not supported by this interface.  Someone also
asked the exact same question here [1].

So yes, locking is required. 

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

[1]. https://stackoverflow.com/questions/18874962/linux-device-driver-file-operations-it-is-possible-to-have-race-conditions

> 
> Regards,
> Arnaud
> 
> > 
> > Thanks,
> > Mathieu
> > 
> >> +	switch (cmd) {
> >> +	case RPMSG_CREATE_EPT_IOCTL:
> >> +		ret = rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo);
> >> +		break;
> >> +
> >> +	case RPMSG_CREATE_DEV_IOCTL:
> >> +		rpdev = rpmsg_create_channel(ctrldev->rpdev, &chinfo);
> >> +		if (!rpdev) {
> >> +			dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name);
> >> +			ret = -ENXIO;
> >> +		}
> >> +		break;
> >> +
> >> +	case RPMSG_RELEASE_DEV_IOCTL:
> >> +		ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo);
> >> +		if (ret)
> >> +			dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n",
> >> +				chinfo.name, ret);
> >> +		break;
> >> +
> >> +	default:
> >> +		ret = -EINVAL;
> >> +	}
> >> +	mutex_unlock(&ctrldev->ctrl_lock);
> >> +
> >> +	return ret;
> >>  };
> >>  
> >>  static const struct file_operations rpmsg_ctrldev_fops = {
> >> @@ -119,6 +147,7 @@ static int rpmsg_ctrldev_probe(struct rpmsg_device *rpdev)
> >>  	device_initialize(dev);
> >>  	dev->parent = &rpdev->dev;
> >>  
> >> +	mutex_init(&ctrldev->ctrl_lock);
> >>  	cdev_init(&ctrldev->cdev, &rpmsg_ctrldev_fops);
> >>  	ctrldev->cdev.owner = THIS_MODULE;
> >>  
> >> diff --git a/include/uapi/linux/rpmsg.h b/include/uapi/linux/rpmsg.h
> >> index f5ca8740f3fb..1637e68177d9 100644
> >> --- a/include/uapi/linux/rpmsg.h
> >> +++ b/include/uapi/linux/rpmsg.h
> >> @@ -33,4 +33,14 @@ struct rpmsg_endpoint_info {
> >>   */
> >>  #define RPMSG_DESTROY_EPT_IOCTL	_IO(0xb5, 0x2)
> >>  
> >> +/**
> >> + * Instantiate a new local rpmsg service device.
> >> + */
> >> +#define RPMSG_CREATE_DEV_IOCTL	_IOW(0xb5, 0x3, struct rpmsg_endpoint_info)
> >> +
> >> +/**
> >> + * Release a local rpmsg device.
> >> + */
> >> +#define RPMSG_RELEASE_DEV_IOCTL	_IOW(0xb5, 0x4, struct rpmsg_endpoint_info)
> >> +
> >>  #endif
> >> -- 
> >> 2.17.1
> >>