[02/12] usb: usbtmc: Support Read Status Byte with SRQ per file handle

* [02/12] usb: usbtmc: Support Read Status Byte with SRQ per file handle
@ 2018-05-17 16:20 Greg Kroah-Hartman
  0 siblings, 0 replies; 12+ messages in thread
From: Greg Kroah-Hartman @ 2018-05-17 16:20 UTC (permalink / raw)
  To: Guido Kiener
  Cc: linux-usb, guido.kiener, pankaj.adhikari, steve_bayless, dpenkler

On Thu, May 17, 2018 at 07:03:26PM +0200, Guido Kiener wrote:
> - Add 'struct usbtmc_file_data' for each file handle to cache last
>   srq_byte (=Status Byte with SRQ) received by usbtmc_interrupt(..)
> 
> - usbtmc488_ioctl_read_stb returns cached srq_byte when available for
>   each file handle to avoid race conditions of concurrent applications.
> 
> - SRQ now sets EPOLLPRI instead of EPOLLIN
> 
> - Caches other values TermChar, TermCharEnabled, auto_abort in
>   'struct usbtmc_file_data' will not be changed by sysfs device
>   attributes during an open file session.
>   Future ioctl functions can change these values.
> 
> - use consistent error return value ETIMEOUT instead of ETIME
> 
> Tested-by: Dave Penkler <dpenkler@gmail.com>
> Reviewed-by: Steve Bayless <steve_bayless@keysight.com>
> Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com>
> ---
>  drivers/usb/class/usbtmc.c | 176 ++++++++++++++++++++++++++++---------
>  1 file changed, 136 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
> index 529295a17579..5754354429d8 100644
> --- a/drivers/usb/class/usbtmc.c
> +++ b/drivers/usb/class/usbtmc.c
> @@ -67,6 +67,7 @@ struct usbtmc_device_data {
>  	const struct usb_device_id *id;
>  	struct usb_device *usb_dev;
>  	struct usb_interface *intf;
> +	struct list_head file_list;
>  
>  	unsigned int bulk_in;
>  	unsigned int bulk_out;
> @@ -87,12 +88,12 @@ struct usbtmc_device_data {
>  	int            iin_interval;
>  	struct urb    *iin_urb;
>  	u16            iin_wMaxPacketSize;
> -	atomic_t       srq_asserted;
>  
>  	/* coalesced usb488_caps from usbtmc_dev_capabilities */
>  	__u8 usb488_caps;
>  
>  	/* attributes from the USB TMC spec for this device */
> +	/* They are used as default values for file_data */
>  	u8 TermChar;
>  	bool TermCharEnabled;
>  	bool auto_abort;
> @@ -104,9 +105,26 @@ struct usbtmc_device_data {
>  	struct mutex io_mutex;	/* only one i/o function running at a time */
>  	wait_queue_head_t waitq;
>  	struct fasync_struct *fasync;
> +	spinlock_t dev_lock; /* lock for file_list */
>  };
>  #define to_usbtmc_data(d) container_of(d, struct usbtmc_device_data, kref)
>  
> +/*
> + * This structure holds private data for each USBTMC file handle.
> + */
> +struct usbtmc_file_data {
> +	struct usbtmc_device_data *data;
> +	struct list_head file_elem;
> +
> +	u8             srq_byte;
> +	atomic_t       srq_asserted;
> +
> +	/* These values are initialized with default values from device_data */
> +	u8             TermChar;
> +	bool           TermCharEnabled;

I don't remember, does TermChar and TermCharEnabled come from a
specification somewhere?  Is that why they are in InterCaps format?

And why duplicate these fields as they are already in the
device-specific data structure?

> +	bool           auto_abort;
> +};
> +
>  /* Forward declarations */
>  static struct usb_driver usbtmc_driver;
>  
> @@ -114,6 +132,7 @@ static void usbtmc_delete(struct kref *kref)
>  {
>  	struct usbtmc_device_data *data = to_usbtmc_data(kref);
>  
> +	pr_debug("%s - called\n", __func__);
>  	usb_put_dev(data->usb_dev);
>  	kfree(data);
>  }
> @@ -122,7 +141,7 @@ static int usbtmc_open(struct inode *inode, struct file *filp)
>  {
>  	struct usb_interface *intf;
>  	struct usbtmc_device_data *data;
> -	int retval = 0;
> +	struct usbtmc_file_data *file_data;
>  
>  	intf = usb_find_interface(&usbtmc_driver, iminor(inode));
>  	if (!intf) {
> @@ -130,21 +149,54 @@ static int usbtmc_open(struct inode *inode, struct file *filp)
>  		return -ENODEV;
>  	}
>  
> +	file_data = kzalloc(sizeof(*file_data), GFP_KERNEL);
> +	if (!file_data)
> +		return -ENOMEM;
> +
> +	pr_debug("%s - called\n", __func__);

Please do not add "tracing" functions like this.  The kernel has a
wonderful built-in function tracing functionality, don't try to write
your own.  These lines should just be removed.

> +
>  	data = usb_get_intfdata(intf);
>  	/* Protect reference to data from file structure until release */
>  	kref_get(&data->kref);
>  
> +	mutex_lock(&data->io_mutex);
> +	file_data->data = data;
> +
> +	/* copy default values from device settings */
> +	file_data->TermChar = data->TermChar;
> +	file_data->TermCharEnabled = data->TermCharEnabled;
> +	file_data->auto_abort = data->auto_abort;
> +
> +	INIT_LIST_HEAD(&file_data->file_elem);
> +	spin_lock_irq(&data->dev_lock);
> +	list_add_tail(&file_data->file_elem, &data->file_list);
> +	spin_unlock_irq(&data->dev_lock);
> +	mutex_unlock(&data->io_mutex);
> +
>  	/* Store pointer in file structure's private data field */
> -	filp->private_data = data;
> +	filp->private_data = file_data;
>  
> -	return retval;
> +	return 0;
>  }
>  
>  static int usbtmc_release(struct inode *inode, struct file *file)
>  {
> -	struct usbtmc_device_data *data = file->private_data;
> +	struct usbtmc_file_data *file_data = file->private_data;
>  
> -	kref_put(&data->kref, usbtmc_delete);
> +	pr_debug("%s - called\n", __func__);

Again, these all need to be dropped.

> +
> +	/* prevent IO _AND_ usbtmc_interrupt */
> +	mutex_lock(&file_data->data->io_mutex);
> +	spin_lock_irq(&file_data->data->dev_lock);
> +
> +	list_del(&file_data->file_elem);
> +
> +	spin_unlock_irq(&file_data->data->dev_lock);
> +	mutex_unlock(&file_data->data->io_mutex);

You protect the list, but what about removing the data itself?

> +
> +	kref_put(&file_data->data->kref, usbtmc_delete);

What protects this from being called at the same time a kref_get is
being called?

Yeah, it previously probably already had this race, sorry I never
noticed that.

> +	file_data->data = NULL;
> +	kfree(file_data);
>  	return 0;
>  }
>  
> @@ -369,10 +421,12 @@ static int usbtmc_ioctl_abort_bulk_out(struct usbtmc_device_data *data)
>  	return rv;
>  }
>  
> -static int usbtmc488_ioctl_read_stb(struct usbtmc_device_data *data,
> +static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
>  				void __user *arg)
>  {
> +	struct usbtmc_device_data *data = file_data->data;
>  	struct device *dev = &data->intf->dev;
> +	int srq_asserted = 0;
>  	u8 *buffer;
>  	u8 tag;
>  	__u8 stb;
> @@ -381,15 +435,27 @@ static int usbtmc488_ioctl_read_stb(struct usbtmc_device_data *data,
>  	dev_dbg(dev, "Enter ioctl_read_stb iin_ep_present: %d\n",
>  		data->iin_ep_present);
>  
> +	spin_lock_irq(&data->dev_lock);
> +	srq_asserted = atomic_xchg(&file_data->srq_asserted, srq_asserted);

That really frightens me. Why are you messing with atomic values here?
What is it supposed to be "protecting" or "doing"?

thanks,

greg k-h
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