Re: [PATCH 2/2] drm: make unplugged flag specific to udl driver

[Haixia Shi <hshi@chromium.org>]

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Regarding the following comment:

> 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);

>Again, you cannot drop this without replacement! In this case, you
>really should wrap fops.release() from UDL and call into drm_release()
>before copying this unplug-logic.

Does this really work? drm_release() will release minor at the end,
regardless of dev->open_count.

If minor is released, can I still safely get dev and call drm_put_dev(dev)
afterwards?

On Tue, Feb 9, 2016 at 4:44 AM, David Herrmann <dh.herrmann@gmail.com>
wrote:

> Hi
>
> On Fri, Feb 5, 2016 at 10:57 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.
>
> I like the idea of moving this hack into udl. However, I don't think
> this patch is sufficient, see below for comments.
>
> Btw., hotplug might happen on other buses as well. It just happens
> that no-one tried pci/platform unplugging so far.. We used to have
> some patches flying around to make it work properly (with enter/leave
> markers), but no-one picked those up. But I like the idea of moving
> this unplugged marker into UDL, to make clear if someone else needs
> it, they better do it properly.
>
> > 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       |  1 +
> >  drivers/gpu/drm/udl/udl_drv.h       |  3 +++
> >  drivers/gpu/drm/udl/udl_fb.c        |  2 +-
> >  drivers/gpu/drm/udl/udl_main.c      | 15 +++++++++++++++
> >  include/drm/drmP.h                  | 14 --------------
> >  11 files changed, 21 insertions(+), 33 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);
> >         }
>
> You cannot just drop this without a replacement. You should add a
> drm_driver.open callback to UDL which checks for this.
> drm_minor_acquire() is only ever called from drm_stub_open(), and as
> such only from drm_open().
>
> Alternatively, you can provide fops.open from UDL and wrap drm_open().
>
> >
> >         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);
> > -
>
> You replace this by moving it into the caller of drm_unplug_dev().
> Sounds good to me. There has never been a real reason to put it
> underneath the global mutex, anyway.
>
> >         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);
>
> Again, you cannot drop this without replacement! In this case, you
> really should wrap fops.release() from UDL and call into drm_release()
> before copying this unplug-logic.
>
> >         }
> >         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;
> > -
>
> Rather than just dropping it, you better move it into udl_drm_gem_mmap().
>
> >         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;
> > -
>
> You *must* provide a wrapper for fops.ioctl() in udl which does this check.
>
> >         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;
> > -
>
> This looks fine to me.
>
> >         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..3cbafe7 100644
> > --- a/drivers/gpu/drm/udl/udl_drv.c
> > +++ b/drivers/gpu/drm/udl/udl_drv.c
> > @@ -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);
>
> This looks good.
>
> >  }
> >
> > diff --git a/drivers/gpu/drm/udl/udl_drv.h
> b/drivers/gpu/drm/udl/udl_drv.h
> > index 4a064ef..61e117a 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 {
> > @@ -140,6 +141,8 @@ 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_main.c
> b/drivers/gpu/drm/udl/udl_main.c
> > index 33dbfb2..f6028a4 100644
> > --- a/drivers/gpu/drm/udl/udl_main.c
> > +++ b/drivers/gpu/drm/udl/udl_main.c
> > @@ -350,3 +350,18 @@ int udl_driver_unload(struct drm_device *dev)
> >         kfree(udl);
> >         return 0;
> >  }
> > +
> > +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;
> > +}
>
> This looks fine to me.
>
> Please make sure to wrap most of the file_operations callbacks in UDL
> and protect them with the "unplugged" check. Yes, we all know that
> this is racy, and always has been. However, it is still better than
> nothing. So please don't just drop them without any explanation!
>
> Thanks
> David
>
> > 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
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
>

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