[PATCH 2/5] drm/xe: Add ref counting for xe_file

[Matthew Brost]

On Tue, Jul 09, 2024 at 09:37:54AM -0700, Umesh Nerlige Ramappa wrote:
> On Tue, Jul 09, 2024 at 10:11:47AM -0500, Lucas De Marchi wrote:
> > On Tue, Jul 09, 2024 at 12:28:43AM GMT, Matthew Brost wrote:
> > > On Mon, Jul 08, 2024 at 04:26:00PM -0700, Umesh Nerlige Ramappa wrote:
> > > > On Mon, Jul 08, 2024 at 05:52:00PM -0500, Lucas De Marchi wrote:
> > > > > On Mon, Jul 08, 2024 at 01:21:00PM GMT, Umesh Nerlige Ramappa wrote:
> > > > > > Add ref counting for xe_file.
> > > > > >
> > > > > > Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
> > > > > > ---
> > > > > > drivers/gpu/drm/xe/xe_device.c       |  7 +++++--
> > > > > > drivers/gpu/drm/xe/xe_device.h       | 12 ++++++++++++
> > > > > > drivers/gpu/drm/xe/xe_device_types.h |  3 +++
> > > > > > 3 files changed, 20 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
> > > > > > index babb697652d5..e6eacf1bcce0 100644
> > > > > > --- a/drivers/gpu/drm/xe/xe_device.c
> > > > > > +++ b/drivers/gpu/drm/xe/xe_device.c
> > > > > > @@ -87,11 +87,14 @@ static int xe_file_open(struct drm_device *dev, struct drm_file *file)
> > > > > > 	spin_unlock(&xe->clients.lock);
> > > > > >
> > > > > > 	file->driver_priv = xef;
> > > > > > +	kref_init(&xef->refcount);
> > > > > > +
> > > > > > 	return 0;
> > > > > > }
> > > > > >
> > > > > > -static void xe_file_destroy(struct xe_file *xef)
> > > > > > +void xe_file_destroy(struct kref *ref)
> > > > > 
> > > > > why do you export this?  I don't think anybody should be calling
> > > > > xe_file_destroy() directly and this function being executed should only
> > > > > be the outcome of kref being 0. Also, if it's exported, it shouldn't
> > > > > really have struct kref as argument, but rather a struct xe_file
> > > > > 
> > > > > 
> > > > > > {
> > > > > > +	struct xe_file *xef = container_of(ref, struct xe_file, refcount);
> > > > > > 	struct xe_device *xe = xef->xe;
> > > > > > 	struct xe_vm *vm;
> > > > > > 	unsigned long idx;
> > > > > > @@ -130,7 +133,7 @@ static void xe_file_close(struct drm_device *dev, struct drm_file *file)
> > > > > > 		xe_exec_queue_put(q);
> > > > > > 	}
> > > > > >
> > > > > > -	xe_file_destroy(xef);
> > > > > > +	xe_file_put(xef);
> > > > > > }
> > > > > >
> > > > > > static const struct drm_ioctl_desc xe_ioctls[] = {
> > > > > > diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
> > > > > > index bb07f5669dbb..2a8b370b1fda 100644
> > > > > > --- a/drivers/gpu/drm/xe/xe_device.h
> > > > > > +++ b/drivers/gpu/drm/xe/xe_device.h
> > > > > > @@ -169,5 +169,17 @@ static inline bool xe_device_wedged(struct xe_device *xe)
> > > > > > }
> > > > > >
> > > > > > void xe_device_declare_wedged(struct xe_device *xe);
> > > > > > +void xe_file_destroy(struct kref *ref);
> > > > > > +
> > > > > > +static inline struct xe_file *xe_file_get(struct xe_file *xef)
> > > > > > +{
> > > > > > +	kref_get(&xef->refcount);
> > > > > > +	return xef;
> > > > > > +}
> > > > > > +
> > > > > > +static inline void xe_file_put(struct xe_file *xef)
> > > > > 
> > > > > I think if you just make this non-inline, passing file_destroy and
> > > > > leave it in the same place, it should work.
> > > > 
> > > > the put is called from xe_exec_queue.c and xe_vm.c also, so passing the
> > > > destroy may not work.
> > > > 
> > > > Based on the patterns below, xe_file_put/xe_file_get will need to be moved
> > > > to xe_device.c and then exported. It looks cleaner, hoping that'w what you
> > > > mean.
> > > > 
> > > > In xe_device.h:
> > > > 
> > > > void xe_file_put(struct xe_file *xef);
> > > > struct xe_file *xe_file_get(struct xe_file *xef);
> > 
> > yes
> 
> ok, posted v2 with this change.
> 
> > 
> > > > 
> > > 
> > > My opinion is the way you have it is correct.
> > > 
> > > Most of Xe is coded this way...
> > > 
> > > mbrost at lstrano-desk:xe$ grep _get\( *.h | grep inline
> > > xe_bo.h:static inline struct xe_bo *xe_bo_get(struct xe_bo *bo)
> > > xe_device.h:static inline struct xe_file *xe_file_get(struct xe_file *xef)
> > > xe_exec_queue.h:static inline struct xe_exec_queue *xe_exec_queue_get(struct xe_exec_queue *q)
> > > xe_lrc.h:static inline struct xe_lrc *xe_lrc_get(struct xe_lrc *lrc)
> > > xe_sched_job.h:static inline struct xe_sched_job *xe_sched_job_get(struct xe_sched_job *job)
> > > xe_vm.h:static inline struct xe_vm *xe_vm_get(struct xe_vm *vm)
> > > 
> > > I'm kinda confused by what Lucas is suggesting.
> > 
> > just don't make xe_file_destroy() non-static, which would basically
> > ignore the refcounting. xe_file_destroy() should rather be local to the
> > .c implementing xe_file_put().
> > 
> 
> In the above instances from grep, most of the destroy helpers are indeed
> exported. Those might need to be changed as per this review comment.
> 

This really just bikeshedding, I prefer static inlines so these being
exported to make get/put as fast as possible. Perhaps this doesn't even
matter with how compilers work these days (e.g. even if exported
functions they get inlined by the compiler?). I don't care enough so
push back though.

I do agree we should be uniform in this though. Maybe the maintainers
set a policy and we follow that everywhere in Xe?

Matt


> Thanks,
> Umesh
> > 
> > Lucas De Marchi