Re: [PATCH v2 01/11] drm/sched: Split drm_sched_job_init

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jul 08, 2021 at 09:53:00AM +0200, Christian König wrote:
> Am 08.07.21 um 09:19 schrieb Daniel Vetter:
> > On Thu, Jul 8, 2021 at 9:09 AM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > > On Thu, Jul 8, 2021 at 8:56 AM Christian König <christian.koenig@amd.com> wrote:
> > > > Am 07.07.21 um 18:32 schrieb Daniel Vetter:
> > > > > On Wed, Jul 7, 2021 at 2:58 PM Christian König <christian.koenig@amd.com> wrote:
> > > > > > Am 07.07.21 um 14:13 schrieb Daniel Vetter:
> > > > > > > On Wed, Jul 7, 2021 at 1:57 PM Christian König <christian.koenig@amd.com> wrote:
> > > > > > > > Am 07.07.21 um 13:14 schrieb Daniel Vetter:
> > > > > > > > > On Wed, Jul 7, 2021 at 11:30 AM Christian König
> > > > > > > > > <christian.koenig@amd.com> wrote:
> > > > > > > > > > Am 02.07.21 um 23:38 schrieb Daniel Vetter:
> > > > > > > > > > > This is a very confusingly named function, because not just does it
> > > > > > > > > > > init an object, it arms it and provides a point of no return for
> > > > > > > > > > > pushing a job into the scheduler. It would be nice if that's a bit
> > > > > > > > > > > clearer in the interface.
> > > > > > > > > > > 
> > > > > > > > > > > But the real reason is that I want to push the dependency tracking
> > > > > > > > > > > helpers into the scheduler code, and that means drm_sched_job_init
> > > > > > > > > > > must be called a lot earlier, without arming the job.
> > > > > > > > > > > 
> > > > > > > > > > > v2:
> > > > > > > > > > > - don't change .gitignore (Steven)
> > > > > > > > > > > - don't forget v3d (Emma)
> > > > > > > > > > > 
> > > > > > > > > > > v3: Emma noticed that I leak the memory allocated in
> > > > > > > > > > > drm_sched_job_init if we bail out before the point of no return in
> > > > > > > > > > > subsequent driver patches. To be able to fix this change
> > > > > > > > > > > drm_sched_job_cleanup() so it can handle being called both before and
> > > > > > > > > > > after drm_sched_job_arm().
> > > > > > > > > > Thinking more about this, I'm not sure if this really works.
> > > > > > > > > > 
> > > > > > > > > > See drm_sched_job_init() was also calling drm_sched_entity_select_rq()
> > > > > > > > > > to update the entity->rq association.
> > > > > > > > > > 
> > > > > > > > > > And that can only be done later on when we arm the fence as well.
> > > > > > > > > Hm yeah, but that's a bug in the existing code I think: We already
> > > > > > > > > fail to clean up if we fail to allocate the fences. So I think the
> > > > > > > > > right thing to do here is to split the checks into job_init, and do
> > > > > > > > > the actual arming/rq selection in job_arm? I'm not entirely sure
> > > > > > > > > what's all going on there, the first check looks a bit like trying to
> > > > > > > > > schedule before the entity is set up, which is a driver bug and should
> > > > > > > > > have a WARN_ON?
> > > > > > > > No you misunderstood me, the problem is something else.
> > > > > > > > 
> > > > > > > > You asked previously why the call to drm_sched_job_init() was so late in
> > > > > > > > the CS.
> > > > > > > > 
> > > > > > > > The reason for this was not alone the scheduler fence init, but also the
> > > > > > > > call to drm_sched_entity_select_rq().
> > > > > > > Ah ok, I think I can fix that. Needs a prep patch to first make
> > > > > > > drm_sched_entity_select infallible, then should be easy to do.
> > > > > > > 
> > > > > > > > > The 2nd check around last_scheduled I have honeslty no idea what it's
> > > > > > > > > even trying to do.
> > > > > > > > You mean that here?
> > > > > > > > 
> > > > > > > >             fence = READ_ONCE(entity->last_scheduled);
> > > > > > > >             if (fence && !dma_fence_is_signaled(fence))
> > > > > > > >                     return;
> > > > > > > > 
> > > > > > > > This makes sure that load balancing is not moving the entity to a
> > > > > > > > different scheduler while there are still jobs running from this entity
> > > > > > > > on the hardware,
> > > > > > > Yeah after a nap that idea crossed my mind too. But now I have locking
> > > > > > > questions, afaiui the scheduler thread updates this, without taking
> > > > > > > any locks - entity dequeuing is lockless. And here we read the fence
> > > > > > > and then seem to yolo check whether it's signalled? What's preventing
> > > > > > > a use-after-free here? There's no rcu or anything going on here at
> > > > > > > all, and it's outside of the spinlock section, which starts a bit
> > > > > > > further down.
> > > > > > The last_scheduled fence of an entity can only change when there are
> > > > > > jobs on the entities queued, and we have just ruled that out in the
> > > > > > check before.
> > > > > There aren't any barriers, so the cpu could easily run the two checks
> > > > > the other way round. I'll ponder this and figure out where exactly we
> > > > > need docs for the constraint and/or barriers to make this work as
> > > > > intended. As-is I'm not seeing how it does ...
> > > > spsc_queue_count() provides the necessary barrier with the atomic_read().
> > > atomic_t is fully unordered, except when it's a read-modify-write
> > Wasn't awake yet, I think the rule is read-modify-write and return
> > previous value gives you full barrier. So stuff like cmpxchg, but also
> > a few others. See atomic_t.txt under ODERING heading (yes that
> > maintainer refuses to accept .rst so I can't just link you to the
> > right section, it's silly). get/set and even RMW atomic ops that don't
> > return anything are all fully unordered.
> 
> As far as I know that not completely correct. The rules around atomics i
> once learned are:
> 
> 1. Everything which modifies something is a write barrier.
> 2. Everything which returns something is a read barrier.
> 
> And I know a whole bunch of use cases where this is relied upon in the core
> kernel, so I'm pretty sure that's correct.

That's against what the doc says, and also it would mean stuff like
atomic_read_acquire or smp_mb__after/before_atomic is completely pointless.

On x86 you're right, anywhere else where there's no total store ordering I
you're wrong.

If there's code that relies on this it needs to be fixed and properly
documented. I did go through the squeue code a bit, and might be better to
just replace this with a core data structure.
-Daniel

> In this case the write barrier is the atomic_dec() in spsc_queue_pop() and
> the read barrier is the aromic_read() in spsc_queue_count().
> 
> The READ_ONCE() is actually not even necessary as far as I can see.
> 
> Christian.
> 
> > -Daniel
> > 
> > 
> > > atomic op, then it's a full barrier. So yeah you need more here. But
> > > also since you only need a read barrier on one side, and a write
> > > barrier on the other, you don't actually need a cpu barriers on x86.
> > > And READ_ONCE gives you the compiler barrier on one side at least, I
> > > haven't found it on the writer side yet.
> > > 
> > > > But yes a comment would be really nice here. I had to think for a while
> > > > why we don't need this as well.
> > > I'm typing a patch, which after a night's sleep I realized has the
> > > wrong barriers. And now I'm also typing some doc improvements for
> > > drm_sched_entity and related functions.
> > > 
> > > > Christian.
> > > > 
> > > > > -Daniel
> > > > > 
> > > > > > Christian.
> > > > > > 
> > > > > > 
> > > > > > > -Daniel
> > > > > > > 
> > > > > > > > Regards
> > > > > > > > Christian.
> > > > > > > > 
> > > > > > > > > -Daniel
> > > > > > > > > 
> > > > > > > > > > Christian.
> > > > > > > > > > 
> > > > > > > > > > > Also improve the kerneldoc for this.
> > > > > > > > > > > 
> > > > > > > > > > > Acked-by: Steven Price <steven.price@arm.com> (v2)
> > > > > > > > > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > > > > > > > > > Cc: Lucas Stach <l.stach@pengutronix.de>
> > > > > > > > > > > Cc: Russell King <linux+etnaviv@armlinux.org.uk>
> > > > > > > > > > > Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
> > > > > > > > > > > Cc: Qiang Yu <yuq825@gmail.com>
> > > > > > > > > > > Cc: Rob Herring <robh@kernel.org>
> > > > > > > > > > > Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> > > > > > > > > > > Cc: Steven Price <steven.price@arm.com>
> > > > > > > > > > > Cc: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
> > > > > > > > > > > Cc: David Airlie <airlied@linux.ie>
> > > > > > > > > > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > > > > > > > > > Cc: Sumit Semwal <sumit.semwal@linaro.org>
> > > > > > > > > > > Cc: "Christian König" <christian.koenig@amd.com>
> > > > > > > > > > > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > > > > > > > > > > Cc: Kees Cook <keescook@chromium.org>
> > > > > > > > > > > Cc: Adam Borowski <kilobyte@angband.pl>
> > > > > > > > > > > Cc: Nick Terrell <terrelln@fb.com>
> > > > > > > > > > > Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > > > > > > > > > > Cc: Paul Menzel <pmenzel@molgen.mpg.de>
> > > > > > > > > > > Cc: Sami Tolvanen <samitolvanen@google.com>
> > > > > > > > > > > Cc: Viresh Kumar <viresh.kumar@linaro.org>
> > > > > > > > > > > Cc: Alex Deucher <alexander.deucher@amd.com>
> > > > > > > > > > > Cc: Dave Airlie <airlied@redhat.com>
> > > > > > > > > > > Cc: Nirmoy Das <nirmoy.das@amd.com>
> > > > > > > > > > > Cc: Deepak R Varma <mh12gx2825@gmail.com>
> > > > > > > > > > > Cc: Lee Jones <lee.jones@linaro.org>
> > > > > > > > > > > Cc: Kevin Wang <kevin1.wang@amd.com>
> > > > > > > > > > > Cc: Chen Li <chenli@uniontech.com>
> > > > > > > > > > > Cc: Luben Tuikov <luben.tuikov@amd.com>
> > > > > > > > > > > Cc: "Marek Olšák" <marek.olsak@amd.com>
> > > > > > > > > > > Cc: Dennis Li <Dennis.Li@amd.com>
> > > > > > > > > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > > > > > > > > > > Cc: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
> > > > > > > > > > > Cc: Sonny Jiang <sonny.jiang@amd.com>
> > > > > > > > > > > Cc: Boris Brezillon <boris.brezillon@collabora.com>
> > > > > > > > > > > Cc: Tian Tao <tiantao6@hisilicon.com>
> > > > > > > > > > > Cc: Jack Zhang <Jack.Zhang1@amd.com>
> > > > > > > > > > > Cc: etnaviv@lists.freedesktop.org
> > > > > > > > > > > Cc: lima@lists.freedesktop.org
> > > > > > > > > > > Cc: linux-media@vger.kernel.org
> > > > > > > > > > > Cc: linaro-mm-sig@lists.linaro.org
> > > > > > > > > > > Cc: Emma Anholt <emma@anholt.net>
> > > > > > > > > > > ---
> > > > > > > > > > >       drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c   |  2 ++
> > > > > > > > > > >       drivers/gpu/drm/amd/amdgpu/amdgpu_job.c  |  2 ++
> > > > > > > > > > >       drivers/gpu/drm/etnaviv/etnaviv_sched.c  |  2 ++
> > > > > > > > > > >       drivers/gpu/drm/lima/lima_sched.c        |  2 ++
> > > > > > > > > > >       drivers/gpu/drm/panfrost/panfrost_job.c  |  2 ++
> > > > > > > > > > >       drivers/gpu/drm/scheduler/sched_entity.c |  6 ++--
> > > > > > > > > > >       drivers/gpu/drm/scheduler/sched_fence.c  | 17 +++++----
> > > > > > > > > > >       drivers/gpu/drm/scheduler/sched_main.c   | 46 +++++++++++++++++++++---
> > > > > > > > > > >       drivers/gpu/drm/v3d/v3d_gem.c            |  2 ++
> > > > > > > > > > >       include/drm/gpu_scheduler.h              |  7 +++-
> > > > > > > > > > >       10 files changed, 74 insertions(+), 14 deletions(-)
> > > > > > > > > > > 
> > > > > > > > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> > > > > > > > > > > index c5386d13eb4a..a4ec092af9a7 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> > > > > > > > > > > @@ -1226,6 +1226,8 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p,
> > > > > > > > > > >           if (r)
> > > > > > > > > > >                   goto error_unlock;
> > > > > > > > > > > 
> > > > > > > > > > > +     drm_sched_job_arm(&job->base);
> > > > > > > > > > > +
> > > > > > > > > > >           /* No memory allocation is allowed while holding the notifier lock.
> > > > > > > > > > >            * The lock is held until amdgpu_cs_submit is finished and fence is
> > > > > > > > > > >            * added to BOs.
> > > > > > > > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
> > > > > > > > > > > index d33e6d97cc89..5ddb955d2315 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
> > > > > > > > > > > @@ -170,6 +170,8 @@ int amdgpu_job_submit(struct amdgpu_job *job, struct drm_sched_entity *entity,
> > > > > > > > > > >           if (r)
> > > > > > > > > > >                   return r;
> > > > > > > > > > > 
> > > > > > > > > > > +     drm_sched_job_arm(&job->base);
> > > > > > > > > > > +
> > > > > > > > > > >           *f = dma_fence_get(&job->base.s_fence->finished);
> > > > > > > > > > >           amdgpu_job_free_resources(job);
> > > > > > > > > > >           drm_sched_entity_push_job(&job->base, entity);
> > > > > > > > > > > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_sched.c b/drivers/gpu/drm/etnaviv/etnaviv_sched.c
> > > > > > > > > > > index feb6da1b6ceb..05f412204118 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/etnaviv/etnaviv_sched.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_sched.c
> > > > > > > > > > > @@ -163,6 +163,8 @@ int etnaviv_sched_push_job(struct drm_sched_entity *sched_entity,
> > > > > > > > > > >           if (ret)
> > > > > > > > > > >                   goto out_unlock;
> > > > > > > > > > > 
> > > > > > > > > > > +     drm_sched_job_arm(&submit->sched_job);
> > > > > > > > > > > +
> > > > > > > > > > >           submit->out_fence = dma_fence_get(&submit->sched_job.s_fence->finished);
> > > > > > > > > > >           submit->out_fence_id = idr_alloc_cyclic(&submit->gpu->fence_idr,
> > > > > > > > > > >                                                   submit->out_fence, 0,
> > > > > > > > > > > diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c
> > > > > > > > > > > index dba8329937a3..38f755580507 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/lima/lima_sched.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/lima/lima_sched.c
> > > > > > > > > > > @@ -129,6 +129,8 @@ int lima_sched_task_init(struct lima_sched_task *task,
> > > > > > > > > > >                   return err;
> > > > > > > > > > >           }
> > > > > > > > > > > 
> > > > > > > > > > > +     drm_sched_job_arm(&task->base);
> > > > > > > > > > > +
> > > > > > > > > > >           task->num_bos = num_bos;
> > > > > > > > > > >           task->vm = lima_vm_get(vm);
> > > > > > > > > > > 
> > > > > > > > > > > diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> > > > > > > > > > > index 71a72fb50e6b..2992dc85325f 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> > > > > > > > > > > @@ -288,6 +288,8 @@ int panfrost_job_push(struct panfrost_job *job)
> > > > > > > > > > >                   goto unlock;
> > > > > > > > > > >           }
> > > > > > > > > > > 
> > > > > > > > > > > +     drm_sched_job_arm(&job->base);
> > > > > > > > > > > +
> > > > > > > > > > >           job->render_done_fence = dma_fence_get(&job->base.s_fence->finished);
> > > > > > > > > > > 
> > > > > > > > > > >           ret = panfrost_acquire_object_fences(job->bos, job->bo_count,
> > > > > > > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > > > > > index 79554aa4dbb1..f7347c284886 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > > > > > @@ -485,9 +485,9 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
> > > > > > > > > > >        * @sched_job: job to submit
> > > > > > > > > > >        * @entity: scheduler entity
> > > > > > > > > > >        *
> > > > > > > > > > > - * Note: To guarantee that the order of insertion to queue matches
> > > > > > > > > > > - * the job's fence sequence number this function should be
> > > > > > > > > > > - * called with drm_sched_job_init under common lock.
> > > > > > > > > > > + * Note: To guarantee that the order of insertion to queue matches the job's
> > > > > > > > > > > + * fence sequence number this function should be called with drm_sched_job_arm()
> > > > > > > > > > > + * under common lock.
> > > > > > > > > > >        *
> > > > > > > > > > >        * Returns 0 for success, negative error code otherwise.
> > > > > > > > > > >        */
> > > > > > > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c
> > > > > > > > > > > index 69de2c76731f..c451ee9a30d7 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/scheduler/sched_fence.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/scheduler/sched_fence.c
> > > > > > > > > > > @@ -90,7 +90,7 @@ static const char *drm_sched_fence_get_timeline_name(struct dma_fence *f)
> > > > > > > > > > >        *
> > > > > > > > > > >        * Free up the fence memory after the RCU grace period.
> > > > > > > > > > >        */
> > > > > > > > > > > -static void drm_sched_fence_free(struct rcu_head *rcu)
> > > > > > > > > > > +void drm_sched_fence_free(struct rcu_head *rcu)
> > > > > > > > > > >       {
> > > > > > > > > > >           struct dma_fence *f = container_of(rcu, struct dma_fence, rcu);
> > > > > > > > > > >           struct drm_sched_fence *fence = to_drm_sched_fence(f);
> > > > > > > > > > > @@ -152,11 +152,10 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f)
> > > > > > > > > > >       }
> > > > > > > > > > >       EXPORT_SYMBOL(to_drm_sched_fence);
> > > > > > > > > > > 
> > > > > > > > > > > -struct drm_sched_fence *drm_sched_fence_create(struct drm_sched_entity *entity,
> > > > > > > > > > > -                                            void *owner)
> > > > > > > > > > > +struct drm_sched_fence *drm_sched_fence_alloc(struct drm_sched_entity *entity,
> > > > > > > > > > > +                                           void *owner)
> > > > > > > > > > >       {
> > > > > > > > > > >           struct drm_sched_fence *fence = NULL;
> > > > > > > > > > > -     unsigned seq;
> > > > > > > > > > > 
> > > > > > > > > > >           fence = kmem_cache_zalloc(sched_fence_slab, GFP_KERNEL);
> > > > > > > > > > >           if (fence == NULL)
> > > > > > > > > > > @@ -166,13 +165,19 @@ struct drm_sched_fence *drm_sched_fence_create(struct drm_sched_entity *entity,
> > > > > > > > > > >           fence->sched = entity->rq->sched;
> > > > > > > > > > >           spin_lock_init(&fence->lock);
> > > > > > > > > > > 
> > > > > > > > > > > +     return fence;
> > > > > > > > > > > +}
> > > > > > > > > > > +
> > > > > > > > > > > +void drm_sched_fence_init(struct drm_sched_fence *fence,
> > > > > > > > > > > +                       struct drm_sched_entity *entity)
> > > > > > > > > > > +{
> > > > > > > > > > > +     unsigned seq;
> > > > > > > > > > > +
> > > > > > > > > > >           seq = atomic_inc_return(&entity->fence_seq);
> > > > > > > > > > >           dma_fence_init(&fence->scheduled, &drm_sched_fence_ops_scheduled,
> > > > > > > > > > >                          &fence->lock, entity->fence_context, seq);
> > > > > > > > > > >           dma_fence_init(&fence->finished, &drm_sched_fence_ops_finished,
> > > > > > > > > > >                          &fence->lock, entity->fence_context + 1, seq);
> > > > > > > > > > > -
> > > > > > > > > > > -     return fence;
> > > > > > > > > > >       }
> > > > > > > > > > > 
> > > > > > > > > > >       module_init(drm_sched_fence_slab_init);
> > > > > > > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > > > > > index 33c414d55fab..5e84e1500c32 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > > > > > @@ -48,9 +48,11 @@
> > > > > > > > > > >       #include <linux/wait.h>
> > > > > > > > > > >       #include <linux/sched.h>
> > > > > > > > > > >       #include <linux/completion.h>
> > > > > > > > > > > +#include <linux/dma-resv.h>
> > > > > > > > > > >       #include <uapi/linux/sched/types.h>
> > > > > > > > > > > 
> > > > > > > > > > >       #include <drm/drm_print.h>
> > > > > > > > > > > +#include <drm/drm_gem.h>
> > > > > > > > > > >       #include <drm/gpu_scheduler.h>
> > > > > > > > > > >       #include <drm/spsc_queue.h>
> > > > > > > > > > > 
> > > > > > > > > > > @@ -569,7 +571,6 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs_ext);
> > > > > > > > > > > 
> > > > > > > > > > >       /**
> > > > > > > > > > >        * drm_sched_job_init - init a scheduler job
> > > > > > > > > > > - *
> > > > > > > > > > >        * @job: scheduler job to init
> > > > > > > > > > >        * @entity: scheduler entity to use
> > > > > > > > > > >        * @owner: job owner for debugging
> > > > > > > > > > > @@ -577,6 +578,9 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs_ext);
> > > > > > > > > > >        * Refer to drm_sched_entity_push_job() documentation
> > > > > > > > > > >        * for locking considerations.
> > > > > > > > > > >        *
> > > > > > > > > > > + * Drivers must make sure drm_sched_job_cleanup() if this function returns
> > > > > > > > > > > + * successfully, even when @job is aborted before drm_sched_job_arm() is called.
> > > > > > > > > > > + *
> > > > > > > > > > >        * Returns 0 for success, negative error code otherwise.
> > > > > > > > > > >        */
> > > > > > > > > > >       int drm_sched_job_init(struct drm_sched_job *job,
> > > > > > > > > > > @@ -594,7 +598,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
> > > > > > > > > > >           job->sched = sched;
> > > > > > > > > > >           job->entity = entity;
> > > > > > > > > > >           job->s_priority = entity->rq - sched->sched_rq;
> > > > > > > > > > > -     job->s_fence = drm_sched_fence_create(entity, owner);
> > > > > > > > > > > +     job->s_fence = drm_sched_fence_alloc(entity, owner);
> > > > > > > > > > >           if (!job->s_fence)
> > > > > > > > > > >                   return -ENOMEM;
> > > > > > > > > > >           job->id = atomic64_inc_return(&sched->job_id_count);
> > > > > > > > > > > @@ -606,13 +610,47 @@ int drm_sched_job_init(struct drm_sched_job *job,
> > > > > > > > > > >       EXPORT_SYMBOL(drm_sched_job_init);
> > > > > > > > > > > 
> > > > > > > > > > >       /**
> > > > > > > > > > > - * drm_sched_job_cleanup - clean up scheduler job resources
> > > > > > > > > > > + * drm_sched_job_arm - arm a scheduler job for execution
> > > > > > > > > > > + * @job: scheduler job to arm
> > > > > > > > > > > + *
> > > > > > > > > > > + * This arms a scheduler job for execution. Specifically it initializes the
> > > > > > > > > > > + * &drm_sched_job.s_fence of @job, so that it can be attached to struct dma_resv
> > > > > > > > > > > + * or other places that need to track the completion of this job.
> > > > > > > > > > > + *
> > > > > > > > > > > + * Refer to drm_sched_entity_push_job() documentation for locking
> > > > > > > > > > > + * considerations.
> > > > > > > > > > >        *
> > > > > > > > > > > + * This can only be called if drm_sched_job_init() succeeded.
> > > > > > > > > > > + */
> > > > > > > > > > > +void drm_sched_job_arm(struct drm_sched_job *job)
> > > > > > > > > > > +{
> > > > > > > > > > > +     drm_sched_fence_init(job->s_fence, job->entity);
> > > > > > > > > > > +}
> > > > > > > > > > > +EXPORT_SYMBOL(drm_sched_job_arm);
> > > > > > > > > > > +
> > > > > > > > > > > +/**
> > > > > > > > > > > + * drm_sched_job_cleanup - clean up scheduler job resources
> > > > > > > > > > >        * @job: scheduler job to clean up
> > > > > > > > > > > + *
> > > > > > > > > > > + * Cleans up the resources allocated with drm_sched_job_init().
> > > > > > > > > > > + *
> > > > > > > > > > > + * Drivers should call this from their error unwind code if @job is aborted
> > > > > > > > > > > + * before drm_sched_job_arm() is called.
> > > > > > > > > > > + *
> > > > > > > > > > > + * After that point of no return @job is committed to be executed by the
> > > > > > > > > > > + * scheduler, and this function should be called from the
> > > > > > > > > > > + * &drm_sched_backend_ops.free_job callback.
> > > > > > > > > > >        */
> > > > > > > > > > >       void drm_sched_job_cleanup(struct drm_sched_job *job)
> > > > > > > > > > >       {
> > > > > > > > > > > -     dma_fence_put(&job->s_fence->finished);
> > > > > > > > > > > +     if (!kref_read(&job->s_fence->finished.refcount)) {
> > > > > > > > > > > +             /* drm_sched_job_arm() has been called */
> > > > > > > > > > > +             dma_fence_put(&job->s_fence->finished);
> > > > > > > > > > > +     } else {
> > > > > > > > > > > +             /* aborted job before committing to run it */
> > > > > > > > > > > +             drm_sched_fence_free(&job->s_fence->finished.rcu);
> > > > > > > > > > > +     }
> > > > > > > > > > > +
> > > > > > > > > > >           job->s_fence = NULL;
> > > > > > > > > > >       }
> > > > > > > > > > >       EXPORT_SYMBOL(drm_sched_job_cleanup);
> > > > > > > > > > > diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> > > > > > > > > > > index 4eb354226972..5c3a99027ecd 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/v3d/v3d_gem.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> > > > > > > > > > > @@ -475,6 +475,8 @@ v3d_push_job(struct v3d_file_priv *v3d_priv,
> > > > > > > > > > >           if (ret)
> > > > > > > > > > >                   return ret;
> > > > > > > > > > > 
> > > > > > > > > > > +     drm_sched_job_arm(&job->base);
> > > > > > > > > > > +
> > > > > > > > > > >           job->done_fence = dma_fence_get(&job->base.s_fence->finished);
> > > > > > > > > > > 
> > > > > > > > > > >           /* put by scheduler job completion */
> > > > > > > > > > > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> > > > > > > > > > > index 88ae7f331bb1..83afc3aa8e2f 100644
> > > > > > > > > > > --- a/include/drm/gpu_scheduler.h
> > > > > > > > > > > +++ b/include/drm/gpu_scheduler.h
> > > > > > > > > > > @@ -348,6 +348,7 @@ void drm_sched_fini(struct drm_gpu_scheduler *sched);
> > > > > > > > > > >       int drm_sched_job_init(struct drm_sched_job *job,
> > > > > > > > > > >                          struct drm_sched_entity *entity,
> > > > > > > > > > >                          void *owner);
> > > > > > > > > > > +void drm_sched_job_arm(struct drm_sched_job *job);
> > > > > > > > > > >       void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
> > > > > > > > > > >                                       struct drm_gpu_scheduler **sched_list,
> > > > > > > > > > >                                          unsigned int num_sched_list);
> > > > > > > > > > > @@ -387,8 +388,12 @@ void drm_sched_entity_set_priority(struct drm_sched_entity *entity,
> > > > > > > > > > >                                      enum drm_sched_priority priority);
> > > > > > > > > > >       bool drm_sched_entity_is_ready(struct drm_sched_entity *entity);
> > > > > > > > > > > 
> > > > > > > > > > > -struct drm_sched_fence *drm_sched_fence_create(
> > > > > > > > > > > +struct drm_sched_fence *drm_sched_fence_alloc(
> > > > > > > > > > >           struct drm_sched_entity *s_entity, void *owner);
> > > > > > > > > > > +void drm_sched_fence_init(struct drm_sched_fence *fence,
> > > > > > > > > > > +                       struct drm_sched_entity *entity);
> > > > > > > > > > > +void drm_sched_fence_free(struct rcu_head *rcu);
> > > > > > > > > > > +
> > > > > > > > > > >       void drm_sched_fence_scheduled(struct drm_sched_fence *fence);
> > > > > > > > > > >       void drm_sched_fence_finished(struct drm_sched_fence *fence);
> > > > > > > > > > > 
> > > 
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll.ch%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C1ac51fc78f9f4e2f08a808d941e0c013%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637613255881294371%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=PRGZl6tUAc7FrL39mu%2BBV2AfC02Mz9R2Neqs5TjdB6M%3D&amp;reserved=0
> > 
> > 
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll.ch%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C1ac51fc78f9f4e2f08a808d941e0c013%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637613255881294371%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=PRGZl6tUAc7FrL39mu%2BBV2AfC02Mz9R2Neqs5TjdB6M%3D&amp;reserved=0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch