On Wed, Feb 19, 2020 at 3:52 PM Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Daniel,
>
> On Wed, Feb 19, 2020 at 03:37:46PM +0100, Daniel Vetter wrote:
> > On Wed, Feb 19, 2020 at 3:22 PM Laurent Pinchart wrote:
> > > On Wed, Feb 19, 2020 at 11:20:54AM +0100, Daniel Vetter wrote:
> > > > We might want to look into pushing this down into drm_mm_init, but
> > > > that would mean rolling out return codes to a pile of functions
> > > > unfortunately. So let's leave that for now.
> > > >
> > > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > > > ---
> > > > drivers/gpu/drm/drm_drv.c | 8 +-------
> > > > drivers/gpu/drm/drm_gem.c | 21 ++++++++++-----------
> > > > drivers/gpu/drm/drm_internal.h | 1 -
> > > > 3 files changed, 11 insertions(+), 19 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > > > index 03a1fb377830..7b3df1188da9 100644
> > > > --- a/drivers/gpu/drm/drm_drv.c
> > > > +++ b/drivers/gpu/drm/drm_drv.c
> > > > @@ -688,13 +688,10 @@ int drm_dev_init(struct drm_device *dev,
> > > >
> > > > ret = drm_dev_set_unique(dev, dev_name(parent));
> > > > if (ret)
> > > > - goto err_setunique;
> > > > + goto err;
> > > >
> > > > return 0;
> > > >
> > > > -err_setunique:
> > > > - if (drm_core_check_feature(dev, DRIVER_GEM))
> > > > - drm_gem_destroy(dev);
> > > > err:
> > > > drm_managed_release(dev);
> > > >
> > > > @@ -756,9 +753,6 @@ EXPORT_SYMBOL(devm_drm_dev_init);
> > > > void drm_dev_fini(struct drm_device *dev)
> > > > {
> > > > drm_vblank_cleanup(dev);
> > > > -
> > > > - if (drm_core_check_feature(dev, DRIVER_GEM))
> > > > - drm_gem_destroy(dev);
> > > > }
> > > > EXPORT_SYMBOL(drm_dev_fini);
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > > > index 0b6e6623735e..31095e0f6b9f 100644
> > > > --- a/drivers/gpu/drm/drm_gem.c
> > > > +++ b/drivers/gpu/drm/drm_gem.c
> > > > @@ -44,6 +44,7 @@
> > > > #include <drm/drm_drv.h>
> > > > #include <drm/drm_file.h>
> > > > #include <drm/drm_gem.h>
> > > > +#include <drm/drm_managed.h>
> > > > #include <drm/drm_print.h>
> > > > #include <drm/drm_vma_manager.h>
> > > >
> > > > @@ -77,6 +78,12 @@
> > > > * up at a later date, and as our interface with shmfs for memory allocation.
> > > > */
> > > >
> > > > +static void
> > > > +drm_gem_init_release(struct drm_device *dev, void *ptr)
> > > > +{
> > > > + drm_vma_offset_manager_destroy(dev->vma_offset_manager);
> > > > +}
> > > > +
> > > > /**
> > > > * drm_gem_init - Initialize the GEM device fields
> > > > * @dev: drm_devic structure to initialize
> > > > @@ -89,7 +96,8 @@ drm_gem_init(struct drm_device *dev)
> > > > mutex_init(&dev->object_name_lock);
> > > > idr_init_base(&dev->object_name_idr, 1);
> > > >
> > > > - vma_offset_manager = kzalloc(sizeof(*vma_offset_manager), GFP_KERNEL);
> > > > + vma_offset_manager = drmm_kzalloc(dev, sizeof(*vma_offset_manager),
> > > > + GFP_KERNEL);
> > > > if (!vma_offset_manager) {
> > > > DRM_ERROR("out of memory\n");
> > > > return -ENOMEM;
> > > > @@ -100,16 +108,7 @@ drm_gem_init(struct drm_device *dev)
> > > > DRM_FILE_PAGE_OFFSET_START,
> > > > DRM_FILE_PAGE_OFFSET_SIZE);
> > > >
> > > > - return 0;
> > > > -}
> > > > -
> > > > -void
> > > > -drm_gem_destroy(struct drm_device *dev)
> > > > -{
> > > > -
> > > > - drm_vma_offset_manager_destroy(dev->vma_offset_manager);
> > > > - kfree(dev->vma_offset_manager);
> > > > - dev->vma_offset_manager = NULL;
> > > > + return drmm_add_action(dev, drm_gem_init_release, NULL);
> > >
> > > This looks fine as such (although I'm not sure if the managed API
> > > overhead is really worth it for core code), but it leads to a potential
> > > issue: if we handle more of the cleanup through the managed API, how do
> > > we ensure that the cleanup functions are called in the right order (when
> > > order matters) ?
> >
> > KASAN essentially (already helped while developing this), plus review.
> > It's still the same problem like reviewing onion unwind code, it's
> > just less fragile for the normal case.
>
> That wasn't really my question though. If there are ordering
> constraints, and if we want to honour them, the ordering of cleanups
> need to be documented in the API (and of course implemented). We may for
> instance want to always do cleanups in the reverse order of the
> allocations.
>
> > I also think that if you have ordering constraints in your drm_device
> > release functions, there's a more fundamental problem going on.
> > Unfortunately we have a lot of these, which is why converting
> > everything in drm, including drivers, is not going to be easy nor
> > quick. There's a lot of problems. E.g. naively converting all
> > drm_connector allocations from devm_kzalloc to drmm_kzalloc still
> > means they get released too early, since the drm_mode_config_init
> > happens before you set up the connectors. So you still have the
> > problem that your connector_funcs->destroy gets called on already
> > freed memory. Lots of work ahead.
>
> Yes that's the kind of issue I was thinking about. We have ordering
> constraints, they will not go away. What's your idea on how to handle
> this ?
drmm_ guarantees that release actions are executed in reverse order of
how they're added. That's the right thing to do in 99% of cases. For
the others you need manual unwind logic, maybe with a combined release
action. Or some some safety checks in your release hook. I think the
drm_minor_alloc conversion is a useful example of some of the problems
that can lurk, and options for handling it all.
-Daniel
>
> > > > }
> > > >
> > > > /**
> > > > diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> > > > index 8c2628dfc6c7..cb09e95a795e 100644
> > > > --- a/drivers/gpu/drm/drm_internal.h
> > > > +++ b/drivers/gpu/drm/drm_internal.h
> > > > @@ -144,7 +144,6 @@ void drm_sysfs_lease_event(struct drm_device *dev);
> > > > /* drm_gem.c */
> > > > struct drm_gem_object;
> > > > int drm_gem_init(struct drm_device *dev);
> > > > -void drm_gem_destroy(struct drm_device *dev);
> > > > int drm_gem_handle_create_tail(struct drm_file *file_priv,
> > > > struct drm_gem_object *obj,
> > > > u32 *handlep);
>
> --
> Regards,
>
> Laurent Pinchart
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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