On Thu, Aug 26, 2021 at 11:04:14AM +0200, Daniel Vetter wrote: > On Thu, Aug 19, 2021 at 11:25:09AM -0400, Andrey Grodzovsky wrote: > > > > On 2021-08-19 5:30 a.m., Daniel Vetter wrote: > > > On Wed, Aug 18, 2021 at 10:51:00AM -0400, Andrey Grodzovsky wrote: > > > > On 2021-08-18 10:42 a.m., Daniel Vetter wrote: > > > > > 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 > > > > > > > > If you look at the original patch it would reinsert it even earlier - right > > > > after stopping the SW scheduler thread, and even then it was to late for > > > > some drivers as they would decide to return back from their TDR handler even > > > > before that. It is solvable but in an ugly way as far as I see, you need to > > > > require each driver in his code to put the job back in the list if they do > > > > it before reaching the place where scheduler framework does it. Kind of > > > > spaghetti code seems to me. > > > Hm yeah I didn't realize this all happens before we stop the scheduler > > > thread. > > > > > > Why can't we stop the scheduler thread first, so that there's guaranteed > > > no race? I've recently had a lot of discussions with panfrost folks about > > > their reset that spawns across engines, and without stopping the scheduler > > > thread first before you touch anything it's just plain impossible. > > > > > > Talked with Christian on that, for each TDR we actually stop all the > > schedulers for all the rings and not only the hanged ring since > > ASIC reset will impact all the rings anyway. So we cannot allow > > other timeout handlers for other rings run in parallel to ours > > as they will stop/restart the threads we just stopped and rely > > on them being stopped. So it's all done with device wide lock > > inside the amdgpu tTDR handler. Only inside the locked > > section then we may stop/restart the scheduler threads. > > Christian also mentioned that you proposed at some point > > to serialize all TDR handling into single threading for all rings - this > > seems > > like something that could be used - we then don't need any > > locking against TDR handlers from other rings and then we may > > stop the scheduler thread as first step > > > > > > > > > > I'm also still not understanding what exactly you guys have done, > > > can someone please dig out the the amdgpu patches that motivate all this > > > maybe that's clearer? A full explanation would still be good since I've > > > only started in scheduler stuff. > > > > > > https://gitlab.freedesktop.org/agd5f/linux/-/commit/de7515d43659f852590645a688f8d493e4a18141 > > Uh, it would have been really good if this was discussed a bit wider > beforehand. Now we have rather diverging approaches to this. Also would be > really good to resurrect the dma_fence annotations too. > > Can you guys pls spend a bit of time on this? Shouldn't be to hard to type > up rfc conversion patches for the other drivers. Ping for this. Currently the hw fence is returned from the ->run_job callback, and that's not great design. If we embed it, then I think it should start existing latest from drm_sched_job_arm. Maybe not yet initialized, but at least allocated. So the right thing to do here is to have the hw fence as a pointer in struct drm_sched_job. And check in drm_sched_job_arm() that it's at least allocated. Otherwise we're just diverging across drivers and tempting them to do the wrong thing with the current ->run_job callback interface. Can you guys look into this? -Daniel > > > Another thing I recently pondered for tdr races looking at i915 code is > > > whether the tdr should first block the completion fence for that job. My > > > motivation is to have a race-free error capture (if the completion races > > > then we might start evicting memory and everything goes boom), but maybe > > > that helps here too. Some kind of atomic "block this fence from > > > completing thing. > > > > > > Or I'm I completely guessing in the wrong direction? > > > > > > I think we already do it here - https://elixir.bootlin.com/linux/v5.14-rc1/source/drivers/gpu/drm/scheduler/sched_main.c#L410 > > Ah yes this works becase drm/sched has separate hw fence from the logical > job fence. > -Daniel > > > > > Andrey > > > > > > > -Daniel > > > > > > > Andrey > > > > > > > > > > > > > > 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 > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch