On Thu, Oct 15, 2015 at 11:06:59AM +0100, Chris Wilson wrote:
> On Thu, Oct 15, 2015 at 11:33:43AM +0200, Daniel Vetter wrote:
> > Compared to wrapping the final kref_put with dev->struct_mutex this
> > allows us to only acquire the offset manager look both in the final
> > cleanup and in the lookup. Which has the upside that no locks leak out
> > of the core abstractions. But it means that we need to hold a
> > temporary reference to the object while checking mmap constraints, to
> > make sure the object doesn't disappear. Extended the critical region
> > would have worked too, but would result in more leaky locking.
> >
> > Also, this is the final bit which required dev->struct_mutex in gem
> > core, now modern drivers can be completely struct_mutex free!
> >
> > This needs a new drm_vma_offset_exact_lookup_locked and makes both
> > drm_vma_offset_exact_lookup and drm_vma_offset_lookup unused.
> >
> > v2: Don't leak object references in failure paths (David).
> >
> > Cc: David Herrmann <dh.herrmann@xxxxxxxxx>
> > Reviewed-by: David Herrmann <dh.herrmann@xxxxxxxxx>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_gem.c | 30 +++++++++++++++++------------
> > drivers/gpu/drm/drm_vma_manager.c | 40 ++++++++++++---------------------------
> > include/drm/drm_vma_manager.h | 22 ++++++---------------
> > 3 files changed, 36 insertions(+), 56 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index ab8ea42264f4..663fadbe979e 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -862,30 +862,36 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
> > {
> > struct drm_file *priv = filp->private_data;
> > struct drm_device *dev = priv->minor->dev;
> > - struct drm_gem_object *obj;
> > + struct drm_gem_object *obj = NULL;
> > struct drm_vma_offset_node *node;
> > int ret;
> >
> > if (drm_device_is_unplugged(dev))
> > return -ENODEV;
> >
>
> /* bla bla bla
> * When the object is being freed, after it hits 0-refcnt
> * it acquires the struct_mutex and proceeds to tear down
> * the object. In the process it will attempt to remove
> * the VMA offset and so acquire this mgr->vm_lock.
> * Therefore if we find an object with a 0-refcnt that matches
> * our range, we know it is in the process of being destroyed
> * and will be freed as soon as we release the lock - so
> * we have to check for the 0-refcnted object and treat it as
> * invalid.
> */
As discussed on irc struct_mutex is just a digression, so I left that part
out when adding your comment.
> > - mutex_lock(&dev->struct_mutex);
> > + drm_vma_offset_lock_lookup(dev->vma_offset_manager);
> > + node = drm_vma_offset_exact_lookup_locked(dev->vma_offset_manager,
> > + vma->vm_pgoff,
> > + vma_pages(vma));
> > + if (likely(node)) {
> > + obj = container_of(node, struct drm_gem_object, vma_node);
> > + if (!kref_get_unless_zero(&obj->refcount))
> > + obj = NULL;
> > + }
> > + drm_vma_offset_unlock_lookup(dev->vma_offset_manager);
>
> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
All four core gem patches now merged in drm-misc, thanks for the review.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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