On 2021-05-18 12:33 p.m., Christian König wrote:
Am 18.05.21 um 18:17 schrieb Andrey Grodzovsky:On 2021-05-18 11:15 a.m., Christian König wrote:Am 18.05.21 um 17:03 schrieb Andrey Grodzovsky:On 2021-05-18 10:07 a.m., Christian König wrote:In a separate discussion with Daniel we once more iterated over the dma_resv requirements and I came to the conclusion that this approach here won't work reliable.The problem is as following:1. device A schedules some rendering with into a buffer and exports it as DMA-buf. 2. device B imports the DMA-buf and wants to consume the rendering, for the the fence of device A is replaced with a new operation. 3. device B is hot plugged and the new operation canceled/newer scheduled.The problem is now that we can't do this since the operation of device A is still running and by signaling our fences we run into the problem of potential memory corruption.By signaling s_fence->finished of the canceled operation from the removed device B we in fact cause memory corruption for the uncompleted job still running on device A ? Because there is someone waiting to read write from the imported buffer on device B and he only waits for the s_fence->finished of device B we signaled in drm_sched_entity_kill_jobs ?Exactly that, yes.In other words when you have a dependency chain like A->B->C then memory management only waits for C before freeing up the memory for example.When C now signaled because the device is hot-plugged before A or B are finished they are essentially accessing freed up memory.
But didn't C imported the BO form B or A in this case ? Why would he be the one releasing that memory ? He would be just dropping his reference to the BO, no ? Also in the general case, drm_sched_entity_fini->drm_sched_entity_kill_jobs which is the one who signals the 'C' fence with error code are as far as I looked called from when the user of that BO is stopping the usage anyway (e.g. drm_driver.postclose callback for when use process closes his device file) who would then access and corrupt the exported memory on device A where the job hasn't completed yet ? Andrey
Christian.AndreyI am not sure this problem you describe above is related to this patch.Well it is kind of related.Here we purely expand the criteria for when sched_entity is considered idle in order to prevent a hang on device remove.And exactly that is problematic. See the jobs on the entity need to cleanly wait for their dependencies before they can be completed.drm_sched_entity_kill_jobs() is also not handling that correctly at the moment, we only wait for the last scheduled fence but not for the dependencies of the job.Were you addressing the patch from yesterday in which you commented that you found a problem with how we finish fences ? It was '[PATCH v7 12/16] drm/amdgpu: Fix hang on device removal.' Also, in the patch series as it is now we only signal HW fences for theextracted device B, we are not touching any other fences. In fact as youmay remember, I dropped all new logic to forcing fence completion in this patch series and only call amdgpu_fence_driver_force_completion for the HW fences of the extracted device as it's done today anyway.Signaling hardware fences is unproblematic since they are emitted when the software scheduling is already completed.Christian.AndreyNot sure how to handle that case. One possibility would be to wait for all dependencies of unscheduled jobs before signaling their fences as canceled.Christian. Am 12.05.21 um 16:26 schrieb Andrey Grodzovsky:Problem: If scheduler is already stopped by the time sched_entity is released and entity's job_queue not empty I encountreda hang in drm_sched_entity_flush. This is because drm_sched_entity_is_idlenever becomes false. Fix: In drm_sched_fini detach all sched_entities from the scheduler's run queues. This will satisfy drm_sched_entity_is_idle. Also wakeup all those processes stuck in sched_entity flushing as the scheduler main thread which wakes them up is stopped by now. v2: Reverse order of drm_sched_rq_remove_entity and marking s_entity as stopped to prevent reinserion back to rq due to race. v3: Drop drm_sched_rq_remove_entity, only modify entity->stopped and check for it in drm_sched_entity_is_idle Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx> Reviewed-by: Christian König <christian.koenig@xxxxxxx> --- drivers/gpu/drm/scheduler/sched_entity.c | 3 ++-drivers/gpu/drm/scheduler/sched_main.c | 24 ++++++++++++++++++++++++2 files changed, 26 insertions(+), 1 deletion(-)diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.cindex 0249c7450188..2e93e881b65f 100644 --- a/drivers/gpu/drm/scheduler/sched_entity.c +++ b/drivers/gpu/drm/scheduler/sched_entity.c@@ -116,7 +116,8 @@ static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity)rmb(); /* for list_empty to work without lock */ if (list_empty(&entity->list) || - spsc_queue_count(&entity->job_queue) == 0) + spsc_queue_count(&entity->job_queue) == 0 || + entity->stopped) return true; return false;diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.cindex 8d1211e87101..a2a953693b45 100644 --- a/drivers/gpu/drm/scheduler/sched_main.c +++ b/drivers/gpu/drm/scheduler/sched_main.c @@ -898,9 +898,33 @@ EXPORT_SYMBOL(drm_sched_init); */ void drm_sched_fini(struct drm_gpu_scheduler *sched) { + struct drm_sched_entity *s_entity; + int i; + if (sched->thread) kthread_stop(sched->thread);+ for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN; i--) {+ struct drm_sched_rq *rq = &sched->sched_rq[i]; + + if (!rq) + continue; + + spin_lock(&rq->lock); + list_for_each_entry(s_entity, &rq->entities, list) + /* + * Prevents reinsertion and marks job_queue as idle, + * it will removed from rq in drm_sched_entity_fini + * eventually + */ + s_entity->stopped = true; + spin_unlock(&rq->lock); + + } ++ /* Wakeup everyone stuck in drm_sched_entity_flush for this scheduler */+ wake_up_all(&sched->job_scheduled); + /* Confirm no work left behind accessing device structures */ cancel_delayed_work_sync(&sched->work_tdr);
