On Fri, Apr 15, 2016 at 03:10:38PM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied@xxxxxxxxxx>
>
> We don't need to hold the fb lock around the initialisation,
> only around the list manipulaton.
>
> So do the lock hold only around the register for now.
> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
This needs a bit more explanation added:
"Previously fb refcounting, and especially the weak reference
(kref_get_unless_zero) used in fb lookups have been protected by fb_lock.
But with the refactoring to share refcounting in the drm_mode_object base
class that switched to being protected by idr_mutex, which means fb_lock
critical sections can be reduced."
I also double-checked that we don't have any outdated comments that point
at the wrong lock, and didn't find any.
With the commit message augmented:
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/drm_crtc.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 0d75517..1863879 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -458,21 +458,22 @@ int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb,
> {
> int ret;
>
> - mutex_lock(&dev->mode_config.fb_lock);
> INIT_LIST_HEAD(&fb->filp_head);
> fb->dev = dev;
> fb->funcs = funcs;
>
> ret = drm_mode_object_get_reg(dev, &fb->base, DRM_MODE_OBJECT_FB,
> - true, drm_framebuffer_free);
> + false, drm_framebuffer_free);
> if (ret)
> goto out;
>
> + mutex_lock(&dev->mode_config.fb_lock);
> dev->mode_config.num_fb++;
> list_add(&fb->head, &dev->mode_config.fb_list);
> -out:
> - mutex_unlock(&dev->mode_config.fb_lock);
>
> + drm_mode_object_register(dev, &fb->base);
> + mutex_unlock(&dev->mode_config.fb_lock);
> +out:
> return ret;
> }
> EXPORT_SYMBOL(drm_framebuffer_init);
> --
> 2.5.5
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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