Hi Arnd!
On 01/02/2014 01:07 PM, Arnd Bergmann wrote:
> interruptible_sleep_on is racy and going away. This replaces
> one use in the radio-cadet driver with an open-coded
> wait loop that lets us check the condition under the mutex
> but sleep without it.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Hans Verkuil <hverkuil@xxxxxxxxx>
> Cc: Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> ---
> drivers/media/radio/radio-cadet.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/radio/radio-cadet.c b/drivers/media/radio/radio-cadet.c
> index 545c04c..67b5bbf 100644
> --- a/drivers/media/radio/radio-cadet.c
> +++ b/drivers/media/radio/radio-cadet.c
> @@ -39,6 +39,7 @@
> #include <linux/pnp.h>
> #include <linux/sched.h>
> #include <linux/io.h> /* outb, outb_p */
> +#include <linux/wait.h>
> #include <media/v4l2-device.h>
> #include <media/v4l2-ioctl.h>
> #include <media/v4l2-ctrls.h>
> @@ -323,25 +324,32 @@ static ssize_t cadet_read(struct file *file, char __user *data, size_t count, lo
> struct cadet *dev = video_drvdata(file);
> unsigned char readbuf[RDS_BUFFER];
> int i = 0;
> + DEFINE_WAIT(wait);
>
> mutex_lock(&dev->lock);
> if (dev->rdsstat == 0)
> cadet_start_rds(dev);
> - if (dev->rdsin == dev->rdsout) {
> + while (1) {
> + prepare_to_wait(&dev->read_queue, &wait, TASK_INTERRUPTIBLE);
> + if (dev->rdsin != dev->rdsout)
> + break;
> +
> if (file->f_flags & O_NONBLOCK) {
> i = -EWOULDBLOCK;
> goto unlock;
> }
> mutex_unlock(&dev->lock);
> - interruptible_sleep_on(&dev->read_queue);
> + schedule();
> mutex_lock(&dev->lock);
> }
> +
This seems overly complicated. Isn't it enough to replace interruptible_sleep_on
by 'wait_event_interruptible(&dev->read_queue, dev->rdsin != dev->rdsout);'?
Or am I missing something subtle?
Regards,
Hans
> while (i < count && dev->rdsin != dev->rdsout)
> readbuf[i++] = dev->rdsbuf[dev->rdsout++];
>
> if (i && copy_to_user(data, readbuf, i))
> i = -EFAULT;
> unlock:
> + finish_wait(&dev->read_queue, &wait);
> mutex_unlock(&dev->lock);
> return i;
> }
>
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