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.
> ---
> 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
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