linux-kernel - Re: [PATCH] drm/sched: Mandate usage of drm_sched_job

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Message-ID: <87f93819aed4784b3e280af38bd7b447821873f5.camel@mailbox.org>
Date: Tue, 14 Oct 2025 13:56:30 +0200
From: Philipp Stanner <phasta@...lbox.org>
To: Tvrtko Ursulin <tursulin@...ulin.net>, Philipp Stanner
 <phasta@...nel.org>,  Matthew Brost <matthew.brost@...el.com>, Danilo
 Krummrich <dakr@...nel.org>, Christian König
 <ckoenig.leichtzumerken@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/sched: Mandate usage of drm_sched_job_cleanup()

On Mon, 2025-10-13 at 13:20 +0100, Tvrtko Ursulin wrote:
> 
> On 26/09/2025 13:36, Philipp Stanner wrote:
> > drm_sched_job_cleanup()'s documentation so far uses relatively soft
> > language, only "recommending" usage of the function. To avoid memory
> > leaks and, potentiall, other bugs, however, the function has to be used.
> > 
> > Demand usage of the function explicitly.
> > 
> > Signed-off-by: Philipp Stanner <phasta@...nel.org>
> > ---
> >   drivers/gpu/drm/scheduler/sched_main.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > index 46119aacb809..0a9df9e61963 100644
> > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > @@ -1030,7 +1030,7 @@ EXPORT_SYMBOL(drm_sched_job_has_dependency);
> >    *
> >    * Cleans up the resources allocated with drm_sched_job_init().
> >    *
> > - * Drivers should call this from their error unwind code if @job is aborted
> > + * Drivers need to call this from their error unwind code if @job is aborted
> 
> Should is indeed wrong. I think it could be better to go with "shall" or 
> "must" though. Since those two are more standard language for this.

"need to" is standard UK(?) English for "must to" I think.

But I'm fine with "must"

> 
> >    * before drm_sched_job_arm() is called.
> >    *
> >    * drm_sched_job_arm() is a point of no return since it initializes the fences
> > @@ -1038,7 +1038,7 @@ EXPORT_SYMBOL(drm_sched_job_has_dependency);
> >    * submit it with drm_sched_entity_push_job() and cannot simply abort it by
> >    * calling drm_sched_job_cleanup().
> >    *
> > - * This function should be called in the &drm_sched_backend_ops.free_job callback.
> > + * This function must be called in the &drm_sched_backend_ops.free_job callback.
> >    */
> >   void drm_sched_job_cleanup(struct drm_sched_job *job)
> >   {
> 
> Hm, having read the thread so far the situation seems not so easy to 
> untangle.
> 
> On one hand I see Matt's point that free_job callback is a bit 
> misleadingly named and that there isn't anything really requiring 
> drm_sched_job_cleanup() to be called exactly from there. Free_job 
> semantics seem to be "job is done, *scheduler* is done with it".
> 
> Drm_sched_job_cleanup() already says it has to be called after the point 
> of no return (arm) so it could be left at drivers discretion (de facto 
> state today) to choose how and when to do it.
> 
> What I did not get is what is actually the perceived problem with 
> letting this stay? (Ie. "should" indicating it is recommended, but not a 
> must/shall.)

I think the most correct formulation with our current mess would be
"cleanup() must be called earliest in free_job(), or later (if there is
a very good reason for that)."

Question would be how to document that.

I still have that big life time docu patch pending. Let me dig into how
I could combine that..


P.

> 
> Regards,
> 
> Tvrtko
>