Re: [PATCH 09/35] drm/gem: support BO freeing without dev->struct_mutex

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 26, 2016 at 05:52:31PM -0400, Alex Deucher wrote:
> On Tue, Apr 26, 2016 at 1:29 PM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > Finally all the core gem and a lot of drivers are entirely free of
> > dev->struct_mutex depencies, and we can start to have an entirely
> > lockless unref path.
> >
> > To make sure that no one who touches the core code accidentally breaks
> > existing drivers which still require dev->struct_mutex I've made the
> > might_lock check unconditional.
> >
> > While at it de-inline the ref/unref functions, they've become a bit
> > too big.
> >
> > v2: Make it not leak like a sieve.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> 
> This and the rest of the series are:
> Acked-by: Alex Deucher <alexander.deucher@amd.com>

Before I pull this in, I'd like at least an r-b on this and one of the
driver patches. t-b even better.
-Daniel

> 
> > ---
> >  drivers/gpu/drm/drm_gem.c | 64 ++++++++++++++++++++++++++++++++++++++---------
> >  include/drm/drmP.h        | 12 ++++++++-
> >  include/drm/drm_gem.h     | 45 ++-------------------------------
> >  3 files changed, 65 insertions(+), 56 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index 25dac31eef37..8f2eff448bb5 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -788,16 +788,7 @@ drm_gem_object_release(struct drm_gem_object *obj)
> >  }
> >  EXPORT_SYMBOL(drm_gem_object_release);
> >
> > -/**
> > - * drm_gem_object_free - free a GEM object
> > - * @kref: kref of the object to free
> > - *
> > - * Called after the last reference to the object has been lost.
> > - * Must be called holding struct_ mutex
> > - *
> > - * Frees the object
> > - */
> > -void
> > +static void
> >  drm_gem_object_free(struct kref *kref)
> >  {
> >         struct drm_gem_object *obj =
> > @@ -806,10 +797,59 @@ drm_gem_object_free(struct kref *kref)
> >
> >         WARN_ON(!mutex_is_locked(&dev->struct_mutex));
> >
> > -       if (dev->driver->gem_free_object != NULL)
> > +       if (dev->driver->gem_free_object_unlocked != NULL)
> > +               dev->driver->gem_free_object_unlocked(obj);
> > +       else if (dev->driver->gem_free_object != NULL)
> >                 dev->driver->gem_free_object(obj);
> >  }
> > -EXPORT_SYMBOL(drm_gem_object_free);
> > +
> > +/**
> > + * drm_gem_object_unreference_unlocked - release a GEM BO reference
> > + * @obj: GEM buffer object
> > + *
> > + * This releases a reference to @obj. Callers must not hold the
> > + * dev->struct_mutex lock when calling this function.
> > + */
> > +void
> > +drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
> > +{
> > +       struct drm_device *dev;
> > +
> > +       if (!obj)
> > +               return;
> > +
> > +       dev = obj->dev;
> > +       might_lock(&dev->struct_mutex);
> > +
> > +       if (dev->driver->gem_free_object != NULL)
> > +               kref_put(&obj->refcount, drm_gem_object_free);
> > +       else if (kref_put_mutex(&obj->refcount, drm_gem_object_free,
> > +                               &dev->struct_mutex))
> > +               mutex_unlock(&dev->struct_mutex);
> > +}
> > +EXPORT_SYMBOL(drm_gem_object_unreference_unlocked);
> > +
> > +/**
> > + * drm_gem_object_unreference - release a GEM BO reference
> > + * @obj: GEM buffer object
> > + *
> > + * This releases a reference to @obj. Callers must hold the dev->struct_mutex
> > + * lock when calling this function, even when the driver doesn't use
> > + * dev->struct_mutex for anything.
> > + *
> > + * For drivers not encumbered with legacy locking use
> > + * drm_gem_object_unreference_unlocked() instead.
> > + */
> > +void
> > +drm_gem_object_unreference(struct drm_gem_object *obj)
> > +{
> > +       if (obj != NULL) {
> > +               WARN_ON(!mutex_is_locked(&obj->dev->struct_mutex));
> > +
> > +               kref_put(&obj->refcount, drm_gem_object_free);
> > +       }
> > +}
> > +EXPORT_SYMBOL(drm_gem_object_unreference);
> >
> >  /**
> >   * drm_gem_vm_open - vma->ops->open implementation for GEM
> > diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> > index c81dd2250fc6..7e30b3d2b25c 100644
> > --- a/include/drm/drmP.h
> > +++ b/include/drm/drmP.h
> > @@ -583,9 +583,19 @@ struct drm_driver {
> >          * Driver-specific constructor for drm_gem_objects, to set up
> >          * obj->driver_private.
> >          *
> > -        * Returns 0 on success.
> > +        * This is deprecated and should not be used by new drivers. Use
> > +        * @gem_free_object_unlocked instead.
> >          */
> >         void (*gem_free_object) (struct drm_gem_object *obj);
> > +
> > +       /**
> > +        * Driver-specific constructor for drm_gem_objects, to set up
> > +        * obj->driver_private. This is for drivers which are not encumbered
> > +        * with dev->struct_mutex legacy locking schemes. Use this hook instead
> > +        * of @gem_free_object.
> > +        */
> > +       void (*gem_free_object_unlocked) (struct drm_gem_object *obj);
> > +
> >         int (*gem_open_object) (struct drm_gem_object *, struct drm_file *);
> >         void (*gem_close_object) (struct drm_gem_object *, struct drm_file *);
> >
> > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> > index 0b3e11ab8757..ae1c7f18eec0 100644
> > --- a/include/drm/drm_gem.h
> > +++ b/include/drm/drm_gem.h
> > @@ -175,7 +175,6 @@ struct drm_gem_object {
> >  };
> >
> >  void drm_gem_object_release(struct drm_gem_object *obj);
> > -void drm_gem_object_free(struct kref *kref);
> >  int drm_gem_object_init(struct drm_device *dev,
> >                         struct drm_gem_object *obj, size_t size);
> >  void drm_gem_private_object_init(struct drm_device *dev,
> > @@ -199,48 +198,8 @@ drm_gem_object_reference(struct drm_gem_object *obj)
> >         kref_get(&obj->refcount);
> >  }
> >
> > -/**
> > - * drm_gem_object_unreference - release a GEM BO reference
> > - * @obj: GEM buffer object
> > - *
> > - * This releases a reference to @obj. Callers must hold the dev->struct_mutex
> > - * lock when calling this function, even when the driver doesn't use
> > - * dev->struct_mutex for anything.
> > - *
> > - * For drivers not encumbered with legacy locking use
> > - * drm_gem_object_unreference_unlocked() instead.
> > - */
> > -static inline void
> > -drm_gem_object_unreference(struct drm_gem_object *obj)
> > -{
> > -       if (obj != NULL) {
> > -               WARN_ON(!mutex_is_locked(&obj->dev->struct_mutex));
> > -
> > -               kref_put(&obj->refcount, drm_gem_object_free);
> > -       }
> > -}
> > -
> > -/**
> > - * drm_gem_object_unreference_unlocked - release a GEM BO reference
> > - * @obj: GEM buffer object
> > - *
> > - * This releases a reference to @obj. Callers must not hold the
> > - * dev->struct_mutex lock when calling this function.
> > - */
> > -static inline void
> > -drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
> > -{
> > -       struct drm_device *dev;
> > -
> > -       if (!obj)
> > -               return;
> > -
> > -       dev = obj->dev;
> > -       if (kref_put_mutex(&obj->refcount, drm_gem_object_free, &dev->struct_mutex))
> > -               mutex_unlock(&dev->struct_mutex);
> > -       else
> > -               might_lock(&dev->struct_mutex);
> > -}
> > +void drm_gem_object_unreference_unlocked(struct drm_gem_object *obj);
> > +void drm_gem_object_unreference(struct drm_gem_object *obj);
> >
> >  int drm_gem_handle_create(struct drm_file *file_priv,
> >                           struct drm_gem_object *obj,
> > --
> > 2.8.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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