On Tue, Mar 21, 2017 at 11:00:23AM +0100, Daniel Vetter wrote:
> On Tue, Mar 21, 2017 at 09:13:53AM +0100, Thierry Reding wrote:
> > From: Thierry Reding <treding@xxxxxxxxxx>
> >
> > Introduce a new top-level lock for the FB helper code. This will allow
> > better locking granularity and avoid the need to abuse modeset locking
> > for this purpose instead.
> >
> > Tested-by: John Stultz <john.stultz@xxxxxxxxxx>
> > Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
>
> Some suggestions below, since I think this state of locking implemented
> here is a bit a too awkwared intermediate thing.
To clarify: After having reviewed the next patch I think this here is
fine. So gets an Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
as-is. I just think we want a notch more here.
But if you're burried too much we can do that as a follow-up too, but in
that case please add a FIXME to e.g. the @lock kernel-doc:
"FIXME: fbdev emulation locking is a mess, long term we want to protect
all helper internal state with this lock, and reduce core KMS locking as
much as possible."
Your choice :-)
Cheers, Daniel
>
> > ---
> > drivers/gpu/drm/drm_fb_helper.c | 27 ++++++++++++++++++++++++++-
> > include/drm/drm_fb_helper.h | 7 +++++++
> > 2 files changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > index 6af80afc4f40..9060adcf7cf8 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -119,6 +119,7 @@ static int __drm_fb_helper_add_one_connector(struct drm_fb_helper *fb_helper,
> > if (!drm_fbdev_emulation)
> > return 0;
> >
> > + WARN_ON(!mutex_is_locked(&fb_helper->lock));
> > WARN_ON(!mutex_is_locked(&fb_helper->dev->mode_config.mutex));
>
> mode_config.mutex isn't needed anymore here (with the recommendations at
> the bottom), please remove.
> >
> > count = fb_helper->connector_count + 1;
> > @@ -141,6 +142,7 @@ static int __drm_fb_helper_add_one_connector(struct drm_fb_helper *fb_helper,
> > drm_connector_get(connector);
> > conn->connector = connector;
> > fb_helper->connector_info[fb_helper->connector_count++] = conn;
> > +
> > return 0;
> > }
> >
> > @@ -149,11 +151,13 @@ int drm_fb_helper_add_one_connector(struct drm_fb_helper *fb_helper,
> > {
> > int err;
> >
> > + mutex_lock(&fb_helper->lock);
> > mutex_lock(&fb_helper->dev->mode_config.mutex);
>
> Same.
>
> >
> > err = __drm_fb_helper_add_one_connector(fb_helper, connector);
> >
> > mutex_unlock(&fb_helper->dev->mode_config.mutex);
> > + mutex_unlock(&fb_helper->lock);
> >
> > return err;
> > }
> > @@ -183,6 +187,7 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
> > if (!drm_fbdev_emulation)
> > return 0;
> >
> > + mutex_lock(&fb_helper->lock);
> > mutex_lock(&dev->mode_config.mutex);
>
> Same.
>
> > drm_connector_list_iter_begin(dev, &conn_iter);
> > drm_for_each_connector_iter(connector, &conn_iter) {
> > @@ -206,6 +211,7 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
> > out:
> > drm_connector_list_iter_end(&conn_iter);
> > mutex_unlock(&dev->mode_config.mutex);
> > + mutex_unlock(&fb_helper->lock);
> >
> > return ret;
> > }
> > @@ -220,6 +226,7 @@ static int __drm_fb_helper_remove_one_connector(struct drm_fb_helper *fb_helper,
> > if (!drm_fbdev_emulation)
> > return 0;
> >
> > + WARN_ON(!mutex_is_locked(&fb_helper->lock));
> > WARN_ON(!mutex_is_locked(&fb_helper->dev->mode_config.mutex));
>
> Same.
>
> >
> > for (i = 0; i < fb_helper->connector_count; i++) {
> > @@ -246,11 +253,13 @@ int drm_fb_helper_remove_one_connector(struct drm_fb_helper *fb_helper,
> > {
> > int err;
> >
> > + mutex_lock(&fb_helper->lock);
> > mutex_lock(&fb_helper->dev->mode_config.mutex);
> >
> > err = __drm_fb_helper_remove_one_connector(fb_helper, connector);
> >
> > mutex_unlock(&fb_helper->dev->mode_config.mutex);
> > + mutex_unlock(&fb_helper->lock);
> >
> > return err;
> > }
> > @@ -502,16 +511,21 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
> > if (!drm_fbdev_emulation)
> > return -ENODEV;
> >
> > + mutex_lock(&fb_helper->lock);
> > drm_modeset_lock_all(dev);
> > +
> > ret = restore_fbdev_mode(fb_helper);
> >
> > do_delayed = fb_helper->delayed_hotplug;
> > if (do_delayed)
> > fb_helper->delayed_hotplug = false;
> > +
> > drm_modeset_unlock_all(dev);
> > + mutex_unlock(&fb_helper->lock);
> >
> > if (do_delayed)
> > drm_fb_helper_hotplug_event(fb_helper);
> > +
> > return ret;
> > }
> > EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked);
> > @@ -747,6 +761,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> > INIT_WORK(&helper->resume_work, drm_fb_helper_resume_worker);
> > INIT_WORK(&helper->dirty_work, drm_fb_helper_dirty_work);
> > helper->dirty_clip.x1 = helper->dirty_clip.y1 = ~0;
> > + mutex_init(&helper->lock);
> > helper->funcs = funcs;
> > helper->dev = dev;
> > }
> > @@ -912,6 +927,7 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
> > }
> > mutex_unlock(&kernel_fb_helper_lock);
> >
> > + mutex_destroy(&fb_helper->lock);
> > drm_fb_helper_crtc_free(fb_helper);
> >
> > }
> > @@ -2421,25 +2437,34 @@ EXPORT_SYMBOL(drm_fb_helper_initial_config);
> > int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
> > {
> > struct drm_device *dev = fb_helper->dev;
> > + int err = 0;
> >
> > if (!drm_fbdev_emulation)
> > return 0;
> >
> > + mutex_lock(&fb_helper->lock);
> > mutex_lock(&dev->mode_config.mutex);
> > +
> > if (!fb_helper->fb || !drm_fb_helper_is_bound(fb_helper)) {
> > fb_helper->delayed_hotplug = true;
> > mutex_unlock(&dev->mode_config.mutex);
> > - return 0;
> > + goto unlock;
> > }
> > +
> > DRM_DEBUG_KMS("\n");
> >
> > drm_setup_crtcs(fb_helper, fb_helper->fb->width, fb_helper->fb->height);
> >
> > mutex_unlock(&dev->mode_config.mutex);
> > + mutex_unlock(&fb_helper->lock);
> >
> > drm_fb_helper_set_par(fb_helper->fbdev);
> >
> > return 0;
> > +
> > +unlock:
> > + mutex_unlock(&fb_helper->lock);
> > + return err;
> > }
> > EXPORT_SYMBOL(drm_fb_helper_hotplug_event);
> >
> > diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> > index 119e5e4609c7..33771d0c44e3 100644
> > --- a/include/drm/drm_fb_helper.h
> > +++ b/include/drm/drm_fb_helper.h
> > @@ -201,6 +201,13 @@ struct drm_fb_helper {
> > struct work_struct resume_work;
> >
> > /**
> > + * @lock:
> > + *
> > + * Top-level FB helper lock.
>
> Bit more detail would be good here.
>
> "This protects all the internal data structures and lists, like
> @connector_info or @crtc_info."
>
> > + */
> > + struct mutex lock;
> > +
> > + /**
> > * @kernel_fb_list:
> > *
> > * Entry on the global kernel_fb_helper_list, used for kgdb entry/exit.
>
> So I think you're missing to protect almost all the fbdev paths.
> Essentially anything looking at crtc_info or connector_info must hold the
> new lock, which means all the places that currently call
> drm_modeset_lock_all() need to grab this new lock too.
>
> Best way to make sure you catch them all is to also update the lockdep
> assert in drm_fb_helper_for_each_connector().
>
> There's still a massive mess going with locking here, especially around
> the probe code and drm_fb_helper_is_bound, but that's a different thing
> and better left for cleanup later on.
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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