Re: [PATCH 4/4] drm/xe/bo: add some annotations in bo_put()

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Sep 10, 2024 at 03:52:26PM +0100, Matthew Auld wrote:
> Hi,
> 
> On 10/09/2024 14:59, Matthew Brost wrote:
> > On Tue, Sep 10, 2024 at 02:11:49PM +0100, Matthew Auld wrote:
> > > If the put() triggers bo destroy then there is at least one potential
> > > sleeping lock. Also annotate bos_lock and ggtt lock.
> > > 
> > > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > > Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> > > Cc: Tejas Upadhyay <tejas.upadhyay@intel.com>
> > > Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
> > > ---
> > >   drivers/gpu/drm/xe/xe_bo.c | 14 ++++++++++++++
> > >   drivers/gpu/drm/xe/xe_bo.h |  6 +-----
> > >   2 files changed, 15 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> > > index 53948a965404..4176b302c38d 100644
> > > --- a/drivers/gpu/drm/xe/xe_bo.c
> > > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > > @@ -2320,6 +2320,20 @@ void xe_bo_put_commit(struct llist_head *deferred)
> > >   		drm_gem_object_free(&bo->ttm.base.refcount);
> > >   }
> > > +void xe_bo_put(struct xe_bo *bo)
> > 
> > These are helpful but thinking we might need a version without asserts
> > that can be used in code paths where we know that we have another ref to
> > the BO. I can already think of a case in the SVM code where this would
> > be needed. In that version maybe we assert the ref count > 1, granted
> > that races but probably the best we can there.
> 
> Yeah, adding another put() variant or similar for that case should be
> totally fine I think.
> 

CI seems to indicate this change is good with the current code base,
will add another variant if / when it is needed.

With that:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> > 
> > What do you think?
> > 
> > Asserts look good though.
> > 
> > Matt
> > 
> > > +{
> > > +	might_sleep();
> > > +	if (bo) {
> > > +#ifdef CONFIG_PROC_FS
> > > +		if (bo->client)
> > > +			might_lock(&bo->client->bos_lock);
> > > +#endif
> > > +		if (bo->ggtt_node && bo->ggtt_node->ggtt)
> > > +			might_lock(&bo->ggtt_node->ggtt->lock);
> > > +		drm_gem_object_put(&bo->ttm.base);
> > > +	}
> > > +}
> > > +
> > >   /**
> > >    * xe_bo_dumb_create - Create a dumb bo as backing for a fb
> > >    * @file_priv: ...
> > > diff --git a/drivers/gpu/drm/xe/xe_bo.h b/drivers/gpu/drm/xe/xe_bo.h
> > > index dbfb3209615d..6e4be52306df 100644
> > > --- a/drivers/gpu/drm/xe/xe_bo.h
> > > +++ b/drivers/gpu/drm/xe/xe_bo.h
> > > @@ -126,11 +126,7 @@ static inline struct xe_bo *xe_bo_get(struct xe_bo *bo)
> > >   	return bo;
> > >   }
> > > -static inline void xe_bo_put(struct xe_bo *bo)
> > > -{
> > > -	if (bo)
> > > -		drm_gem_object_put(&bo->ttm.base);
> > > -}
> > > +void xe_bo_put(struct xe_bo *bo);
> > >   static inline void __xe_bo_unset_bulk_move(struct xe_bo *bo)
> > >   {
> > > -- 
> > > 2.46.0
> > >