Am Dienstag, den 25.06.2019, 09:04 +0200 schrieb Johan Hovold:
> On Mon, Jun 24, 2019 at 10:33:23AM +0200, Oliver Neukum wrote:
> > If you deregister a device you need to wake up all waiters
> > as there will be no further wakeups.
> >
> > Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
> > ---
> > drivers/gnss/core.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c
> > index e6f94501cb28..0d13bd2cefd5 100644
> > --- a/drivers/gnss/core.c
> > +++ b/drivers/gnss/core.c
> > @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev)
> > down_write(&gdev->rwsem);
> > gdev->disconnected = true;
> > if (gdev->count) {
> > - wake_up_interruptible(&gdev->read_queue);
> > + wake_up_interruptible_all(&gdev->read_queue);
>
> GNSS core doesn't have any exclusive waiters, so no need to use use the
> exclusive wake-up (all) interface.
Well, yes, but that is the problem. In gnss_read() you drop the lock:
mutex_lock(&gdev->read_mutex);
while (kfifo_is_empty(&gdev->read_fifo)) {
mutex_unlock(&gdev->read_mutex);
if (gdev->disconnected)
return 0;
if (file->f_flags & O_NONBLOCK)
return -EAGAIN;
That means that an arbitrary number of tasks can get here.
ret = wait_event_interruptible(gdev->read_queue,
gdev->disconnected ||
!kfifo_is_empty(&gdev->read_fifo));
Meaning that an arbitrary number can be sleeping here. Yet in
gnss_deregister_device() you use a simple wake_up:
void gnss_deregister_device(struct gnss_device *gdev)
{
down_write(&gdev->rwsem);
gdev->disconnected = true;
if (gdev->count) {
wake_up_interruptible(&gdev->read_queue);
wake_up_interruptible() will wake up one waiting task. But after that
the device is gone. There will be no further events. The other tasks
will sleep forever.
Regards
Oliver
