On Sun, Feb 03, 2019 at 04:41:55PM +0100, Noralf Trønnes wrote:
> If userspace has open fd(s) when drm_dev_unplug() is run, it will result
> in drm_dev_unregister() being called twice. First in drm_dev_unplug() and
> then later in drm_release() through the call to drm_put_dev().
>
> Since userspace already holds a ref on drm_device through the drm_minor,
> it's not necessary to add extra ref counting based on no open file
> handles. Instead just drm_dev_put() unconditionally in drm_dev_unplug().
>
> We now has this:
> - Userpace holds a ref on drm_device as long as there's open fd(s)
> - The driver holds a ref on drm_device as long as it's bound to the
> struct device
>
> When both sides are done with drm_device, it is released.
>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
Reviewed-by: Sean Paul <sean@xxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_drv.c | 6 +-----
> drivers/gpu/drm/drm_file.c | 6 ++----
> 2 files changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 381581b01d48..05bbc2b622fc 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -376,11 +376,7 @@ void drm_dev_unplug(struct drm_device *dev)
> synchronize_srcu(&drm_unplug_srcu);
>
> drm_dev_unregister(dev);
> -
> - mutex_lock(&drm_global_mutex);
> - if (dev->open_count == 0)
> - drm_dev_put(dev);
> - mutex_unlock(&drm_global_mutex);
> + drm_dev_put(dev);
> }
> EXPORT_SYMBOL(drm_dev_unplug);
>
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 46f48f245eb5..3f20f598cd7c 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -479,11 +479,9 @@ int drm_release(struct inode *inode, struct file *filp)
>
> drm_file_free(file_priv);
>
> - if (!--dev->open_count) {
> + if (!--dev->open_count)
> drm_lastclose(dev);
> - if (drm_dev_is_unplugged(dev))
> - drm_put_dev(dev);
> - }
> +
> mutex_unlock(&drm_global_mutex);
>
> drm_minor_release(minor);
> --
> 2.20.1
>
--
Sean Paul, Software Engineer, Google / Chromium OS
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