by Arnaud Pouliquen

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Subject: Re: [PATCH 1/4] rpmsg: ctrl: Introduce RPMSG_CREATE_DEV_IOCTL

On 6/16/21 10:12 AM, Arnaud POULIQUEN wrote:
> Hello Mathieu,
>
> On 6/15/21 7:53 PM, Mathieu Poirier wrote:
>> On Fri, Jun 04, 2021 at 11:14:03AM +0200, Arnaud Pouliquen wrote:
>>> Implement the RPMSG_CREATE_DEV_IOCTL to allow the user application to
>>> initiate a communication through a new rpmsg channel.
>>> This 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.
>>>
>>> Suggested-by: Mathieu Poirier <[email protected]>
>>> Signed-off-by: Arnaud Pouliquen <[email protected]>
>>> ---
>>> drivers/rpmsg/rpmsg_ctrl.c | 30 ++++++++++++++++++++++++++----
>>> include/uapi/linux/rpmsg.h | 5 +++++
>>> 2 files changed, 31 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
>>> index eeb1708548c1..4aa962df3661 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 +84,26 @@ 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);
>>
>> Do we need a lock here? I thought the character device layer would guarantee
>> accesses on a file handler would be atomic... Am I wrong?
>>
>
> It is a good point! from my understanding, using "unlocked_ioctl" ops, the
> driver has to handle is own atomic protection.
> I will try to hack the code to verify this.

I confirm without lock there is no atomic access, re-entrance is possible in
rpmsg_ctrldev_ioctl. Keeping lock to serialize the controls seems safer to me to
avoid race condition.

Regards
Arnaud

>
> Thanks,
> Arnaud
>
>>> + 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;
>>> +
>>> + default:
>>> + ret = -EINVAL;
>>> + }
>>> + mutex_unlock(&ctrldev->ctrl_lock);
>>> +
>>> + return ret;
>>> };
>>>
>>> static const struct file_operations rpmsg_ctrldev_fops = {
>>> @@ -119,6 +140,7 @@ 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..f9d5a74e7801 100644
>>> --- a/include/uapi/linux/rpmsg.h
>>> +++ b/include/uapi/linux/rpmsg.h
>>> @@ -33,4 +33,9 @@ struct rpmsg_endpoint_info {
>>> */
>>> #define RPMSG_DESTROY_EPT_IOCTL _IO(0xb5, 0x2)
>>>
>>> +/**
>>> + * Instantiate a rpmsg service device.
>>> + */
>>> +#define RPMSG_CREATE_DEV_IOCTL _IOW(0xb5, 0x3, struct rpmsg_endpoint_info)
>>> +
>>> #endif
>>> --
>>> 2.17.1
>>>