On Tue, Nov 15, 2022 at 10:30:01AM +0100, Andrzej Hajda wrote:
> On 13.07.2021 15:59, Daniel Vetter wrote:
> > 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_...@module-reload.html
> > Signed-off-by: Daniel Vetter <daniel.vet...@intel.com>
> > Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
> > Cc: Chris Wilson <ch...@chris-wilson.co.uk>
> > Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
> > Cc: Maxime Ripard <mrip...@kernel.org>
> > Cc: Thomas Zimmermann <tzimmerm...@suse.de>
> > Cc: David Airlie <airl...@linux.ie>
> > Cc: Daniel Vetter <dan...@ffwll.ch>
>
> Reviewed-by: Andrzej Hajda <andrzej.ha...@intel.com>
I just dropped this one from my patch pile a while ago, because there were
conflicts. If you like it, feel free to resurrect&rebase and then merge it
(but maybe cc intel-gfx so the CI there can test it).
-Daniel
>
> Regards
> Andrzej
>
> > ---
> > 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);
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
