On Sun, Nov 6, 2022 at 12:54 PM Oded Gabbay <ogabbay@xxxxxxxxxx> wrote:
>
> On Thu, Nov 3, 2022 at 7:26 AM Jiho Chu <jiho.chu@xxxxxxxxxxx> wrote:
> >
> > On Wed, 2 Nov 2022 22:34:04 +0200
> > Oded Gabbay <ogabbay@xxxxxxxxxx> wrote:
> >
> > > +/**
> > > + * accel_open - open method for ACCEL file
> > > + * @inode: device inode
> > > + * @filp: file pointer.
> > > + *
> > > + * This function must be used by drivers as their &file_operations.open method.
> > > + * It looks up the correct ACCEL device and instantiates all the per-file
> > > + * resources for it. It also calls the &drm_driver.open driver callback.
> > > + *
> > > + * Return: 0 on success or negative errno value on failure.
> > > + */
> > > +int accel_open(struct inode *inode, struct file *filp)
> > > +{
> > > + struct drm_device *dev;
> > > + struct drm_minor *minor;
> > > + int retcode;
> > > +
> > > + minor = accel_minor_acquire(iminor(inode));
> > > + if (IS_ERR(minor))
> > > + return PTR_ERR(minor);
> > > +
> > > + dev = minor->dev;
> > > +
> > > + atomic_fetch_inc(&dev->open_count);
> > > +
> >
> > Hi,
> > It needs to consider drm_global_mutex to access open_count.
> > please check doxy of open_count.
> Now that I'm changing the code back to be part of drm.ko, I can return
> all the code that is in drm_copy which I removed for this to compile.
I take it back. All the code that I omitted was for legacy drivers.
If you look inside drm_dev_needs_global_mutex(), you will see 3 cases
where you need to take the global mutex, and all 3 are only relevant
for legacy drivers and/or drivers that use deprecated features.
So, I disagree with your original comment here.
Moreover, open_count is atomic, so I don't need to take the mutex to
increment it, and as you can see in drm_open(), the function
increments it regardless of whether it takes
drm_dev_needs_global_mutex.
Oded
>
> >
> >
> > > + /* share address_space across all char-devs of a single device */
> > > + filp->f_mapping = dev->anon_inode->i_mapping;
> > > +
> > > + retcode = drm_open_helper(filp, minor);
> > > + if (retcode)
> > > + goto err_undo;
> > > +
> > > + return 0;
> > > +
> > > +err_undo:
> > > + atomic_dec(&dev->open_count);
> > > + accel_minor_release(minor);
> > > + return retcode;
> > > +}
> > > +EXPORT_SYMBOL_GPL(accel_open);
> > > +
> > > static int accel_stub_open(struct inode *inode, struct file *filp)
> > > {
> > > - DRM_DEBUG("Operation not supported");
> > > + const struct file_operations *new_fops;
> > > + struct drm_minor *minor;
> > > + int err;
> > > +
> > > + DRM_DEBUG("\n");
> >
> > It seems useless.
> Correct, I removed it in v3.
> Thanks,
> Oded
> >
> > Thanks.
> > Jiho Chu
