Some vague evidences suggests this can go wrong. Try to prevent it by holding the right mutex and clearing ->deferred_setup to make sure we later on don't accidentally try to re-register the fbdev when the driver thought it had it all cleaned up already. v2: I realized that this is fundamentally butchered, and CI complained about lockdep splats. So limit the critical section again and just add a few notes what the proper fix is. References: https://intel-gfx-ci.01.org/tree/linux-next/next-20201215/fi-byt-j1900/igt@i915_pm_rpm@xxxxxxxxxxxxxxxxxx Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> Cc: Maxime Ripard <mripard@xxxxxxxxxx> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> Cc: David Airlie <airlied@xxxxxxxx> Cc: Daniel Vetter <daniel@xxxxxxxx> --- drivers/gpu/drm/drm_fb_helper.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index 9d82fda274eb..8f11e5abb222 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -598,6 +598,9 @@ EXPORT_SYMBOL(drm_fb_helper_alloc_fbi); * A wrapper around unregister_framebuffer, to release the fb_info * framebuffer device. This must be called before releasing all resources for * @fb_helper by calling drm_fb_helper_fini(). + * + * Note that this is fundamentally racy on hotunload because it doen't handle + * open fbdev file descriptors at all. Use drm_fbdev_generic_setup() instead. */ void drm_fb_helper_unregister_fbi(struct drm_fb_helper *fb_helper) { @@ -611,6 +614,9 @@ EXPORT_SYMBOL(drm_fb_helper_unregister_fbi); * @fb_helper: driver-allocated fbdev helper, can be NULL * * This cleans up all remaining resources associated with @fb_helper. + * + * Note that this is fundamentally racy on hotunload because it doen't handle + * open fbdev file descriptors at all. Use drm_fbdev_generic_setup() instead. */ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper) { @@ -2382,6 +2388,10 @@ static void drm_fbdev_client_unregister(struct drm_client_dev *client) { struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); + mutex_lock(&fb_helper->lock); + fb_helper->deferred_setup = false; + mutex_unlock(&fb_helper->lock); + if (fb_helper->fbdev) /* drm_fbdev_fb_destroy() takes care of cleanup */ drm_fb_helper_unregister_fbi(fb_helper); -- 2.32.0
