On Wed, Apr 25, 2018 at 12:56:45PM +0200, Johan Hovold wrote:
> On Wed, Apr 25, 2018 at 10:56:49AM +0200, Greg Kroah-Hartman wrote:
> > On Tue, Apr 24, 2018 at 06:34:52PM +0200, Johan Hovold wrote:
> > > +static int gnss_open(struct inode *inode, struct file *file)
> > > +{
> > > + struct gnss_device *gdev;
> > > + int ret = 0;
> > > +
> > > + gdev = container_of(inode->i_cdev, struct gnss_device, cdev);
> > > +
> > > + get_device(&gdev->dev);
> > > +
> > > + nonseekable_open(inode, file);
> > > + file->private_data = gdev;
> > > +
> > > + down_write(&gdev->rwsem);
> >
> > Just curious, why a rwsem? They can be slower than a normal semaphore,
> > is this really a contentious lock?
>
> I use the rwsem to deal with hotplugging; the underlying device can go
> away at any time and the core makes sure that no further calls into the
> corresponding driver is made once all currently executing callbacks
> return.
I just did find one access to the gnss ops which was unsafe however; the
existence check for a write_raw callback in write() needs to be replaced
by a device flag.
Thanks,
Johan
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