Also note that it is not currently feasible for UDL code to access
drm_global_mutex.

Please also refer to the similar comments ("FIXME: open_count is protected
by drm_global_mutex but that would lead to locking inversion with the
driver load path.") in nouveau, i915 and amdgpu.

On Wed, Feb 10, 2016 at 12:51 PM, Haixia Shi <hshi@chromium.org> wrote:

> > This should rather be:
> >
> >         drm_release(inode, filp);
> >         mutex_lock(&drm_global_mutex);
> >         if (!dev->open_count && udl_device_is_unplugged(dev))
> >                 drm_put_dev(dev);
> >         mutex_unlock(&drm_global_mutex);
> >
> >         return 0;
> >
> > There is no reason to look at the return code of drm_release(), ever.
>
> But drm_release() does return a retcode. It would still make sense to
> return that as-is in case any existing code relies on it.
>
> On Wed, Feb 10, 2016 at 4:24 AM, David Herrmann <dh.herrmann@gmail.com>
> wrote:
>
>> Hi
>>
>> On Tue, Feb 9, 2016 at 10:05 PM, Haixia Shi <hshi@chromium.org> wrote:
>> > Remove the general drm_device_is_unplugged() checks, and move the
>> unplugged
>> > flag handling logic into drm/udl. In general we want to keep
>> driver-specific
>> > logic out of common drm code.
>> >
>> > Signed-off-by: Haixia Shi <hshi@chromium.org>
>> > Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
>> > ---
>> >  drivers/gpu/drm/drm_drv.c           |  6 ----
>> >  drivers/gpu/drm/drm_fops.c          |  2 --
>> >  drivers/gpu/drm/drm_gem.c           |  3 --
>> >  drivers/gpu/drm/drm_ioctl.c         |  3 --
>> >  drivers/gpu/drm/drm_vm.c            |  3 --
>> >  drivers/gpu/drm/udl/udl_connector.c |  2 +-
>> >  drivers/gpu/drm/udl/udl_drv.c       |  7 +++--
>> >  drivers/gpu/drm/udl/udl_drv.h       |  6 ++++
>> >  drivers/gpu/drm/udl/udl_fb.c        |  2 +-
>> >  drivers/gpu/drm/udl/udl_gem.c       |  5 +++
>> >  drivers/gpu/drm/udl/udl_main.c      | 61
>> +++++++++++++++++++++++++++++++++++++
>> >  include/drm/drmP.h                  | 14 ---------
>> >  12 files changed, 78 insertions(+), 36 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
>> > index 167c8d3..f93ee12 100644
>> > --- a/drivers/gpu/drm/drm_drv.c
>> > +++ b/drivers/gpu/drm/drm_drv.c
>> > @@ -376,9 +376,6 @@ struct drm_minor *drm_minor_acquire(unsigned int
>> minor_id)
>> >
>> >         if (!minor) {
>> >                 return ERR_PTR(-ENODEV);
>> > -       } else if (drm_device_is_unplugged(minor->dev)) {
>> > -               drm_dev_unref(minor->dev);
>> > -               return ERR_PTR(-ENODEV);
>> >         }
>> >
>> >         return minor;
>> > @@ -464,9 +461,6 @@ void drm_unplug_dev(struct drm_device *dev)
>> >         drm_minor_unregister(dev, DRM_MINOR_CONTROL);
>> >
>> >         mutex_lock(&drm_global_mutex);
>> > -
>> > -       drm_device_set_unplugged(dev);
>> > -
>> >         if (dev->open_count == 0) {
>> >                 drm_put_dev(dev);
>> >         }
>> > diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
>> > index 1ea8790..b4332d4 100644
>> > --- a/drivers/gpu/drm/drm_fops.c
>> > +++ b/drivers/gpu/drm/drm_fops.c
>> > @@ -497,8 +497,6 @@ int drm_release(struct inode *inode, struct file
>> *filp)
>> >
>> >         if (!--dev->open_count) {
>> >                 retcode = drm_lastclose(dev);
>> > -               if (drm_device_is_unplugged(dev))
>> > -                       drm_put_dev(dev);
>> >         }
>> >         mutex_unlock(&drm_global_mutex);
>> >
>> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> > index 2e8c77e..c622e32 100644
>> > --- a/drivers/gpu/drm/drm_gem.c
>> > +++ b/drivers/gpu/drm/drm_gem.c
>> > @@ -900,9 +900,6 @@ int drm_gem_mmap(struct file *filp, struct
>> vm_area_struct *vma)
>> >         struct drm_vma_offset_node *node;
>> >         int ret;
>> >
>> > -       if (drm_device_is_unplugged(dev))
>> > -               return -ENODEV;
>> > -
>> >         drm_vma_offset_lock_lookup(dev->vma_offset_manager);
>> >         node =
>> drm_vma_offset_exact_lookup_locked(dev->vma_offset_manager,
>> >                                                   vma->vm_pgoff,
>> > diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
>> > index 8ce2a0c..f959074 100644
>> > --- a/drivers/gpu/drm/drm_ioctl.c
>> > +++ b/drivers/gpu/drm/drm_ioctl.c
>> > @@ -695,9 +695,6 @@ long drm_ioctl(struct file *filp,
>> >
>> >         dev = file_priv->minor->dev;
>> >
>> > -       if (drm_device_is_unplugged(dev))
>> > -               return -ENODEV;
>> > -
>> >         is_driver_ioctl = nr >= DRM_COMMAND_BASE && nr <
>> DRM_COMMAND_END;
>> >
>> >         if (is_driver_ioctl) {
>> > diff --git a/drivers/gpu/drm/drm_vm.c b/drivers/gpu/drm/drm_vm.c
>> > index f90bd5f..3a68be4 100644
>> > --- a/drivers/gpu/drm/drm_vm.c
>> > +++ b/drivers/gpu/drm/drm_vm.c
>> > @@ -657,9 +657,6 @@ int drm_legacy_mmap(struct file *filp, struct
>> vm_area_struct *vma)
>> >         struct drm_device *dev = priv->minor->dev;
>> >         int ret;
>> >
>> > -       if (drm_device_is_unplugged(dev))
>> > -               return -ENODEV;
>> > -
>> >         mutex_lock(&dev->struct_mutex);
>> >         ret = drm_mmap_locked(filp, vma);
>> >         mutex_unlock(&dev->struct_mutex);
>> > diff --git a/drivers/gpu/drm/udl/udl_connector.c
>> b/drivers/gpu/drm/udl/udl_connector.c
>> > index 4709b54..b168f2c 100644
>> > --- a/drivers/gpu/drm/udl/udl_connector.c
>> > +++ b/drivers/gpu/drm/udl/udl_connector.c
>> > @@ -96,7 +96,7 @@ static int udl_mode_valid(struct drm_connector
>> *connector,
>> >  static enum drm_connector_status
>> >  udl_detect(struct drm_connector *connector, bool force)
>> >  {
>> > -       if (drm_device_is_unplugged(connector->dev))
>> > +       if (udl_device_is_unplugged(connector->dev))
>> >                 return connector_status_disconnected;
>> >         return connector_status_connected;
>> >  }
>> > diff --git a/drivers/gpu/drm/udl/udl_drv.c
>> b/drivers/gpu/drm/udl/udl_drv.c
>> > index d5728ec..f5c2a97 100644
>> > --- a/drivers/gpu/drm/udl/udl_drv.c
>> > +++ b/drivers/gpu/drm/udl/udl_drv.c
>> > @@ -24,12 +24,12 @@ static const struct vm_operations_struct
>> udl_gem_vm_ops = {
>> >
>> >  static const struct file_operations udl_driver_fops = {
>> >         .owner = THIS_MODULE,
>> > -       .open = drm_open,
>> > +       .open = udl_drm_open,
>> >         .mmap = udl_drm_gem_mmap,
>> >         .poll = drm_poll,
>> >         .read = drm_read,
>> > -       .unlocked_ioctl = drm_ioctl,
>> > -       .release = drm_release,
>> > +       .unlocked_ioctl = udl_drm_ioctl,
>> > +       .release = udl_drm_release,
>> >  #ifdef CONFIG_COMPAT
>> >         .compat_ioctl = drm_compat_ioctl,
>> >  #endif
>> > @@ -97,6 +97,7 @@ static void udl_usb_disconnect(struct usb_interface
>> *interface)
>> >         drm_connector_unplug_all(dev);
>> >         udl_fbdev_unplug(dev);
>> >         udl_drop_usb(dev);
>> > +       udl_device_set_unplugged(dev);
>> >         drm_unplug_dev(dev);
>> >  }
>> >
>> > diff --git a/drivers/gpu/drm/udl/udl_drv.h
>> b/drivers/gpu/drm/udl/udl_drv.h
>> > index 4a064ef..75aa91c 100644
>> > --- a/drivers/gpu/drm/udl/udl_drv.h
>> > +++ b/drivers/gpu/drm/udl/udl_drv.h
>> > @@ -65,6 +65,7 @@ struct udl_device {
>> >         atomic_t bytes_identical; /* saved effort with backbuffer
>> comparison */
>> >         atomic_t bytes_sent; /* to usb, after compression including
>> overhead */
>> >         atomic_t cpu_kcycles_used; /* transpired during pixel
>> processing */
>> > +       atomic_t unplugged; /* device has been unplugged or gone away */
>> >  };
>> >
>> >  struct udl_gem_object {
>> > @@ -133,6 +134,9 @@ int udl_gem_get_pages(struct udl_gem_object *obj);
>> >  void udl_gem_put_pages(struct udl_gem_object *obj);
>> >  int udl_gem_vmap(struct udl_gem_object *obj);
>> >  void udl_gem_vunmap(struct udl_gem_object *obj);
>> > +int udl_drm_open(struct inode *inode, struct file *filp);
>> > +int udl_drm_release(struct inode *inode, struct file *filp);
>> > +int udl_drm_ioctl(struct file *filp, unsigned int cmd, unsigned long
>> arg);
>> >  int udl_drm_gem_mmap(struct file *filp, struct vm_area_struct *vma);
>> >  int udl_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf);
>> >
>> > @@ -140,6 +144,8 @@ int udl_handle_damage(struct udl_framebuffer *fb,
>> int x, int y,
>> >                       int width, int height);
>> >
>> >  int udl_drop_usb(struct drm_device *dev);
>> > +void udl_device_set_unplugged(struct drm_device *dev);
>> > +int udl_device_is_unplugged(struct drm_device *dev);
>> >
>> >  #define CMD_WRITE_RAW8   "\xAF\x60" /**< 8 bit raw write command. */
>> >  #define CMD_WRITE_RL8    "\xAF\x61" /**< 8 bit run length command. */
>> > diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c
>> > index 200419d..df1d53e 100644
>> > --- a/drivers/gpu/drm/udl/udl_fb.c
>> > +++ b/drivers/gpu/drm/udl/udl_fb.c
>> > @@ -325,7 +325,7 @@ static int udl_fb_open(struct fb_info *info, int
>> user)
>> >         struct udl_device *udl = dev->dev_private;
>> >
>> >         /* If the USB device is gone, we don't accept new opens */
>> > -       if (drm_device_is_unplugged(udl->ddev))
>> > +       if (udl_device_is_unplugged(udl->ddev))
>> >                 return -ENODEV;
>> >
>> >         ufbdev->fb_count++;
>> > diff --git a/drivers/gpu/drm/udl/udl_gem.c
>> b/drivers/gpu/drm/udl/udl_gem.c
>> > index 2a0a784..33c302f 100644
>> > --- a/drivers/gpu/drm/udl/udl_gem.c
>> > +++ b/drivers/gpu/drm/udl/udl_gem.c
>> > @@ -86,8 +86,13 @@ int udl_dumb_create(struct drm_file *file,
>> >
>> >  int udl_drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
>> >  {
>> > +       struct drm_file *priv = filp->private_data;
>> > +       struct drm_device *dev = priv->minor->dev;
>> >         int ret;
>> >
>> > +       if (udl_device_is_unplugged(dev))
>> > +               return -ENODEV;
>> > +
>> >         ret = drm_gem_mmap(filp, vma);
>> >         if (ret)
>> >                 return ret;
>> > diff --git a/drivers/gpu/drm/udl/udl_main.c
>> b/drivers/gpu/drm/udl/udl_main.c
>> > index 33dbfb2..2ba3ee3 100644
>> > --- a/drivers/gpu/drm/udl/udl_main.c
>> > +++ b/drivers/gpu/drm/udl/udl_main.c
>> > @@ -350,3 +350,64 @@ int udl_driver_unload(struct drm_device *dev)
>> >         kfree(udl);
>> >         return 0;
>> >  }
>> > +
>> > +int udl_drm_open(struct inode *inode, struct file *filp)
>> > +{
>> > +       struct drm_file *file_priv;
>> > +       struct drm_minor *minor;
>> > +
>> > +       int ret = drm_open(inode, filp);
>> > +       if (ret)
>> > +               return ret;
>> > +
>> > +       file_priv = filp->private_data;
>> > +       minor = file_priv->minor;
>> > +       if (udl_device_is_unplugged(minor->dev)) {
>> > +               drm_dev_unref(minor->dev);
>> > +               return -ENODEV;
>> > +       }
>>
>> This doesn't make sense to me. You're called here with global-mutex
>> held, so you can just check udl_device_is_unplugged() before calling
>> into drm_open().
>>
>> > +
>> > +       return 0;
>> > +}
>> > +
>> > +int udl_drm_release(struct inode *inode, struct file *filp)
>> > +{
>> > +       struct drm_file *file_priv = filp->private_data;
>> > +       struct drm_device *dev = file_priv->minor->dev;
>> > +
>> > +       int ret = drm_release(inode, filp);
>> > +       if (!dev->open_count && udl_device_is_unplugged(dev))
>> > +               drm_put_dev(dev);
>>
>> This should rather be:
>>
>>         drm_release(inode, filp);
>>         mutex_lock(&drm_global_mutex);
>>         if (!dev->open_count && udl_device_is_unplugged(dev))
>>                 drm_put_dev(dev);
>>         mutex_unlock(&drm_global_mutex);
>>
>>         return 0;
>>
>> There is no reason to look at the return code of drm_release(), ever.
>>
>> > +
>> > +       return ret;
>> > +}
>> > +
>> > +int udl_drm_ioctl(struct file *filp, unsigned int cmd, unsigned long
>> arg)
>> > +{
>> > +       struct drm_file *file_priv = filp->private_data;
>> > +       struct drm_device *dev = file_priv->minor->dev;
>> > +       unsigned int nr = DRM_IOCTL_NR(cmd);
>> > +
>> > +       if (udl_device_is_unplugged(dev) &&
>> > +               nr != DRM_IOCTL_NR(DRM_IOCTL_MODE_SETCRTC) &&
>> > +               nr != DRM_IOCTL_NR(DRM_IOCTL_MODE_RMFB) &&
>> > +               nr != DRM_IOCTL_NR(DRM_IOCTL_MODE_DESTROY_DUMB))
>> > +               return -ENODEV;
>>
>> Why?
>>
>> Just do:
>>
>>         if (udl_device_is_unplugged(dev))
>>                 return -ENODEV;
>>
>> Why this complex logic here?
>>
>> Thanks
>> David
>>
>> > +
>> > +       return drm_ioctl(filp, cmd, arg);
>> > +}
>> > +
>> > +void udl_device_set_unplugged(struct drm_device *dev)
>> > +{
>> > +       struct udl_device *udl = dev->dev_private;
>> > +       smp_wmb();
>> > +       atomic_set(&udl->unplugged, 1);
>> > +}
>> > +
>> > +int udl_device_is_unplugged(struct drm_device *dev)
>> > +{
>> > +       struct udl_device *udl = dev->dev_private;
>> > +       int ret = atomic_read(&udl->unplugged);
>> > +       smp_rmb();
>> > +       return ret;
>> > +}
>> > diff --git a/include/drm/drmP.h b/include/drm/drmP.h
>> > index d7162cf..40c6099 100644
>> > --- a/include/drm/drmP.h
>> > +++ b/include/drm/drmP.h
>> > @@ -748,7 +748,6 @@ struct drm_device {
>> >         struct drm_minor *control;              /**< Control node */
>> >         struct drm_minor *primary;              /**< Primary node */
>> >         struct drm_minor *render;               /**< Render node */
>> > -       atomic_t unplugged;                     /**< Flag whether dev
>> is dead */
>> >         struct inode *anon_inode;               /**< inode for private
>> address-space */
>> >         char *unique;                           /**< unique name of the
>> device */
>> >         /*@} */
>> > @@ -879,19 +878,6 @@ static __inline__ int
>> drm_core_check_feature(struct drm_device *dev,
>> >         return ((dev->driver->driver_features & feature) ? 1 : 0);
>> >  }
>> >
>> > -static inline void drm_device_set_unplugged(struct drm_device *dev)
>> > -{
>> > -       smp_wmb();
>> > -       atomic_set(&dev->unplugged, 1);
>> > -}
>> > -
>> > -static inline int drm_device_is_unplugged(struct drm_device *dev)
>> > -{
>> > -       int ret = atomic_read(&dev->unplugged);
>> > -       smp_rmb();
>> > -       return ret;
>> > -}
>> > -
>> >  static inline bool drm_is_render_client(const struct drm_file
>> *file_priv)
>> >  {
>> >         return file_priv->minor->type == DRM_MINOR_RENDER;
>> > --
>> > 2.7.0.rc3.207.g0ac5344
>> >
>>
>
>