On Thu, Aug 19, 2021 at 03:01:26AM +0000, Liu, Monk wrote:
> [AMD Official Use Only]
>
> Hi Andrey and Daniel
>
> We worked for a really long time on this new feature to AMD that finally
> can pick up the bad job from all timedout ones, and the change in
> scheduler (get/put fence in drm_sched_job_timedout, and remove the bad
> job delete and put back) is the last piece for us.
>
> While we understand and realized that after the "bad job list node
> delete logic" being removed from job_timedout, there will be race
> issues introduced if vendor's job_timeout calback is accessing the bad
> job in parallel of scheduler doing "sched->ops->free_job(leanup_job)".
>
> And to not introduce impact at all on those vendors I'd like to proposal
> a very simple change (which introduced a new bool member for scheduler
> to indicate if the del/put-back logic is needed or not) , check patch
> here below:
If everyone operates like that then the shared code becomes a massive mess
of incompatible options and unmaintainable. I don't think that's a good
path forward.
-Daniel
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> index 47ea468..5e0bdc4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> @@ -495,6 +495,8 @@ int amdgpu_fence_driver_init_ring(struct amdgpu_ring *ring,
> return r;
> }
>
> + ring->sched.keep_bad_job = true;
> +
> return 0;
> }
>
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 92d8de2..e7ac384 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -314,6 +314,7 @@ static void drm_sched_job_timedout(struct work_struct *work)
> {
> struct drm_gpu_scheduler *sched;
> struct drm_sched_job *job;
> + struct dma_fence *f = NULL;
>
> sched = container_of(work, struct drm_gpu_scheduler, work_tdr.work);
>
> @@ -328,7 +329,11 @@ static void drm_sched_job_timedout(struct work_struct *work)
> * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
> * is parked at which point it's safe.
> */
> - list_del_init(&job->list);
> + if (sched->keep_bad_job == false)
> + list_del_init(&job->list);
> + else
> + f = dma_fence_get(job->s_fence->parent);//get parent fence here to prevent hw_fence dropping to zero due to sched-main's cleanup_jobs, for amdgpu once parent fence drop to zero the sched_job will be kfree-ed
> +
> spin_unlock(&sched->job_list_lock);
>
> job->sched->ops->timedout_job(job);
> @@ -341,6 +346,8 @@ static void drm_sched_job_timedout(struct work_struct *work)
> job->sched->ops->free_job(job);
> sched->free_guilty = false;
> }
> +
> + dma_fence_put(f);
> } else {
> spin_unlock(&sched->job_list_lock);
> }
> @@ -396,7 +403,7 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
> * (earlier) cleanups and drm_sched_get_cleanup_job will not be called
> * now until the scheduler thread is unparked.
> */
> - if (bad && bad->sched == sched)
> + if (bad && bad->sched == sched && sched->keep_bad_job == false)
> /*
> * Add at the head of the queue to reflect it was the earliest
> * job extracted.
> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> index 4ea8606..5f9a640 100644
> --- a/include/drm/gpu_scheduler.h
> +++ b/include/drm/gpu_scheduler.h
> @@ -301,6 +301,7 @@ struct drm_gpu_scheduler {
> atomic_t _score;
> bool ready;
> bool free_guilty;
> + bool keep_bad_job;
> };
>
> int drm_sched_init(struct drm_gpu_scheduler *sched,
>
>
> Thanks
>
> ------------------------------------------
> Monk Liu | Cloud-GPU Core team
> ------------------------------------------
>
> -----Original Message-----
> From: Daniel Vetter <daniel@xxxxxxxx>
> Sent: Wednesday, August 18, 2021 10:43 PM
> To: Grodzovsky, Andrey <Andrey.Grodzovsky@xxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>; Alex Deucher <alexdeucher@xxxxxxxxx>; Chen, JingWen <JingWen.Chen2@xxxxxxx>; Maling list - DRI developers <dri-devel@xxxxxxxxxxxxxxxxxxxxx>; amd-gfx list <amd-gfx@xxxxxxxxxxxxxxxxxxxxx>; Liu, Monk <Monk.Liu@xxxxxxx>; Koenig, Christian <Christian.Koenig@xxxxxxx>
> Subject: Re: [PATCH v2] Revert "drm/scheduler: Avoid accessing freed bad job."
>
> On Wed, Aug 18, 2021 at 10:36:32AM -0400, Andrey Grodzovsky wrote:
> >
> > On 2021-08-18 10:32 a.m., Daniel Vetter wrote:
> > > On Wed, Aug 18, 2021 at 10:26:25AM -0400, Andrey Grodzovsky wrote:
> > > > On 2021-08-18 10:02 a.m., Alex Deucher wrote:
> > > >
> > > > > + dri-devel
> > > > >
> > > > > Since scheduler is a shared component, please add dri-devel on
> > > > > all scheduler patches.
> > > > >
> > > > > On Wed, Aug 18, 2021 at 7:21 AM Jingwen Chen <Jingwen.Chen2@xxxxxxx> wrote:
> > > > > > [Why]
> > > > > > for bailing job, this commit will delete it from pending list
> > > > > > thus the bailing job will never have a chance to be
> > > > > > resubmitted even in advance tdr mode.
> > > > > >
> > > > > > [How]
> > > > > > after embeded hw_fence into amdgpu_job is done, the race
> > > > > > condition that this commit tries to work around is completely
> > > > > > solved.So revert this commit.
> > > > > > This reverts commit 135517d3565b48f4def3b1b82008bc17eb5d1c90.
> > > > > > v2:
> > > > > > add dma_fence_get/put() around timedout_job to avoid
> > > > > > concurrent delete during processing timedout_job
> > > > > >
> > > > > > Signed-off-by: Jingwen Chen <Jingwen.Chen2@xxxxxxx>
> > > > > > ---
> > > > > > drivers/gpu/drm/scheduler/sched_main.c | 23 +++++------------------
> > > > > > 1 file changed, 5 insertions(+), 18 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > index a2a953693b45..f9b9b3aefc4a 100644
> > > > > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > @@ -314,6 +314,7 @@ static void drm_sched_job_timedout(struct work_struct *work)
> > > > > > {
> > > > > > struct drm_gpu_scheduler *sched;
> > > > > > struct drm_sched_job *job;
> > > > > > + struct dma_fence *fence;
> > > > > > enum drm_gpu_sched_stat status =
> > > > > > DRM_GPU_SCHED_STAT_NOMINAL;
> > > > > >
> > > > > > sched = container_of(work, struct drm_gpu_scheduler,
> > > > > > work_tdr.work); @@ -325,11 +326,10 @@ static void
> > > > > > drm_sched_job_timedout(struct work_struct *work)
> > > > > >
> > > > > > if (job) {
> > > > > > /*
> > > > > > - * Remove the bad job so it cannot be freed by concurrent
> > > > > > - * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
> > > > > > - * is parked at which point it's safe.
> > > > > > + * Get job->s_fence->parent here to avoid concurrent delete during
> > > > > > + * processing timedout_job
> > > > > > */
> > > > > > - list_del_init(&job->list);
> > > > > > + fence = dma_fence_get(job->s_fence->parent);
> > > >
> > > > While this is true for amdgpu, it has no meaning for other drivers
> > > > for whom we haven't done the refactoring of embedding HW fence
> > > > (parent) into the job structure.
> > > > In fact thinking
> > > > about it, unless you do the HW fence embedding for all the drivers
> > > > using the scheduler you cannot revert this patch or you will just
> > > > break them.
> > > btw, why did you do that embedding? I do still have my patches with
> > > dma_fence annotations floating around, but my idea at least was to
> > > fix that issue with a mempool, not with embeddeding. What was the
> > > motivation for embedding the wh fence?
> > > -Daniel
> >
> >
> > The motivation was 2 fold, avoid memory allocation during jobs
> > submissions (HW fence allocation) because as Christian explained this
> > leads to deadlock with mm code during evictions due to memory pressure
> > (Christian can clarify if I messed
>
> Yeah that's the exact same thing I've chased with my dma_fence annotations, but thus far zero to none interested in getting it sorted. I think it'd be good to have some cross-driver agreement on how this should be solved before someone just charges ahead ...
>
> > this explanation). Second is to exactly revert this patch because
> > while it solved the issue described in the patch it created another
> > with drivers who baildc out early during TDR handling for various
> > reason and the job would just leak because it was already removed form
> > pending list.
>
> Can't we reinsert it before we restart the scheduler thread? It might need a separate list for that due to the lockless queue tricks. Or am I thinking about the wrong kind of "we lost the job"?
> -Danile
>
> >
> > Andrey
> >
> >
> > >
> > >
> > > > Andrey
> > > >
> > > >
> > > > > > spin_unlock(&sched->job_list_lock);
> > > > > >
> > > > > > status = job->sched->ops->timedout_job(job);
> > > > > > @@ -342,6 +342,7 @@ static void drm_sched_job_timedout(struct work_struct *work)
> > > > > > job->sched->ops->free_job(job);
> > > > > > sched->free_guilty = false;
> > > > > > }
> > > > > > + dma_fence_put(fence);
> > > > > > } else {
> > > > > > spin_unlock(&sched->job_list_lock);
> > > > > > }
> > > > > > @@ -392,20 +393,6 @@ void drm_sched_stop(struct
> > > > > > drm_gpu_scheduler *sched, struct drm_sched_job *bad)
> > > > > >
> > > > > > kthread_park(sched->thread);
> > > > > >
> > > > > > - /*
> > > > > > - * Reinsert back the bad job here - now it's safe as
> > > > > > - * drm_sched_get_cleanup_job cannot race against us and release the
> > > > > > - * bad job at this point - we parked (waited for) any in progress
> > > > > > - * (earlier) cleanups and drm_sched_get_cleanup_job will not be called
> > > > > > - * now until the scheduler thread is unparked.
> > > > > > - */
> > > > > > - if (bad && bad->sched == sched)
> > > > > > - /*
> > > > > > - * Add at the head of the queue to reflect it was the earliest
> > > > > > - * job extracted.
> > > > > > - */
> > > > > > - list_add(&bad->list, &sched->pending_list);
> > > > > > -
> > > > > > /*
> > > > > > * Iterate the job list from later to earlier one and either deactive
> > > > > > * their HW callbacks or remove them from pending
> > > > > > list if they already
> > > > > > --
> > > > > > 2.25.1
> > > > > >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll.ch%2F&data=04%7C01%7Cmonk.liu%40amd.com%7C8ddd8838028242eb82c708d9625678cf%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637648945806335873%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=uFdAwQH6yWm%2FC%2FdDeG8wXKNsOqI7dSQRGO9NbKkjYyU%3D&reserved=0
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
