On Sat, Jul 15, 2017 at 12:02:47PM +0100, Chris Wilson wrote:
> Quoting Daniel Vetter (2017-07-15 10:53:28)
> > For modern drivers the DRM core doesn't use struct_mutex at all, which
> > means it's defacto a driver-private lock. But since we still need it
> > for legacy drivers we can't initialize it in drivers, which means all
> > the different instances share one lockdep key. Despite that they might
> > be placed in totally different places in the locking hierarchy.
> >
> > This results in a lot of bogus lockdep splats when running stuff on
> > systems with multiple gpus. Partially remedy the situation by only
> > doing might_lock checks on drivers that do use struct_mutex still for
> > gem locking.
> >
> > A more complete solution would be to do the mutex_init in the drm core
> > only for legacy drivers, plus add it to each modern driver that still
> > needs it, which would also give each its own lockdep key. Trying to do
> > that dynamically doesn't work, because lockdep requires it's keys to
> > be statically allocated.
> >
> > Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
> > Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
> > Cc: Jiri Slaby <jirislaby@xxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
>
> But fwiw, the patch isn't wrong and fixes a false positive, so
> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>
> > drivers/gpu/drm/drm_gem.c | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index 8dc11064253d..9663a79dd363 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -826,13 +826,15 @@ drm_gem_object_put_unlocked(struct drm_gem_object *obj)
> > return;
> >
> > dev = obj->dev;
> > - might_lock(&dev->struct_mutex);
> >
> > if (dev->driver->gem_free_object_unlocked)
>
> coding-style nit, if one branch needs {} they all need {}.
> (The real reason why I didn't want to move might_lock around in this
> function ;)
Fixed while applying, thanks for your review.
-Daniel
>
> > kref_put(&obj->refcount, drm_gem_object_free);
> > - else if (kref_put_mutex(&obj->refcount, drm_gem_object_free,
> > + else {
> > + might_lock(&dev->struct_mutex);
> > + if (kref_put_mutex(&obj->refcount, drm_gem_object_free,
> > &dev->struct_mutex))
> > - mutex_unlock(&dev->struct_mutex);
> > + mutex_unlock(&dev->struct_mutex);
> > + }
> > }
> > EXPORT_SYMBOL(drm_gem_object_put_unlocked);
> _______________________________________________
> dri-devel mailing list
> dri-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
