[PATCH 09/35] drm/gem: support BO freeing without dev->struct_mutex
Daniel Vetter
daniel at ffwll.ch
Wed Apr 27 11:21:13 UTC 2016
On Wed, Apr 27, 2016 at 11:31:00AM +0200, Lucas Stach wrote:
> Am Dienstag, den 26.04.2016, 19:29 +0200 schrieb Daniel Vetter:
> > 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 at intel.com>
>
> Two mostly cosmetic comments below, otherwise looks good:
>
> Reviewed-by: Lucas Stach <l.stach at pengutronix.de>
>
> > ---
> > 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)
>
> Why those explicit != NULL checks? The style mostly used in this file is
> to omit those, like "if (dev->driver->gem_free_object_unlocked)". Same
> comment applies to several hunks of this patch.
I move some of these functions around, the != NULL checks where there
already. I can easily change all the ones I touch.
> > + 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 part of the comment is really off. I see it's just copy&paste from
> the comment above gem_free_object, but I think it should have been
> placed above gem_open_object and has nothing to do with the free*
> callbacks.
Oops, wanted to add proper kerneldoc for this new hook and the old one to
explain the differences, and totally failed at that. Will fix up.
-Daniel
>
> > 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,
>
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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