From: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
To: "Christian König" <christian.koenig@amd.com>,
dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
linux-pci@vger.kernel.org, ckoenig.leichtzumerken@gmail.com,
daniel.vetter@ffwll.ch, Harry.Wentland@amd.com
Cc: ppaalanen@gmail.com, Alexander.Deucher@amd.com,
gregkh@linuxfoundation.org, helgaas@kernel.org,
Felix.Kuehling@amd.com
Subject: Re: [PATCH v7 13/16] drm/scheduler: Fix hang when sched_entity released
Date: Tue, 18 May 2021 13:43:52 -0400 [thread overview]
Message-ID: <ec157a35-85fb-11e5-226a-c25d699102c6@amd.com> (raw)
In-Reply-To: <8228ea6b-4faf-bb7e-aaf4-8949932e869a@amd.com>
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.
>
>>
>> Andrey
>>
>>>>
>>>>
>>>> I 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 the
>>>> extracted device B, we are not touching any other fences. In fact as
>>>> you
>>>> may 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.
>>>
>>>>
>>>> Andrey
>>>>
>>>>>
>>>>> Not 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 encountred
>>>>>> a hang in drm_sched_entity_flush. This is because
>>>>>> drm_sched_entity_is_idle
>>>>>> never 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@amd.com>
>>>>>> Reviewed-by: Christian König <christian.koenig@amd.com>
>>>>>> ---
>>>>>> 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.c
>>>>>> index 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.c
>>>>>> index 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);
>>>>>
>>>
>
next prev parent reply other threads:[~2021-05-18 17:43 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 14:26 [PATCH v7 00/16] RFC Support hot device unplug in amdgpu Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 01/16] drm/ttm: Remap all page faults to per process dummy page Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 02/16] drm/amdgpu: Split amdgpu_device_fini into early and late Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 03/16] drm/amdkfd: Split kfd suspend from device exit Andrey Grodzovsky
2021-05-12 20:33 ` Felix Kuehling
2021-05-12 20:38 ` Andrey Grodzovsky
2021-05-20 3:20 ` [PATCH] drm/amdgpu: Add early fini callback Andrey Grodzovsky
2021-05-20 3:29 ` Felix Kuehling
2021-05-20 3:58 ` Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 04/16] " Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 05/16] drm/amdgpu: Handle IOMMU enabled case Andrey Grodzovsky
2021-05-14 14:41 ` Andrey Grodzovsky
2021-05-14 16:25 ` Felix Kuehling
2021-05-14 16:26 ` Andrey Grodzovsky
2021-05-17 14:38 ` [PATCH] " Andrey Grodzovsky
2021-05-17 14:48 ` Felix Kuehling
2021-05-12 14:26 ` [PATCH v7 06/16] drm/amdgpu: Remap all page faults to per process dummy page Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 07/16] PCI: Add support for dev_groups to struct pci_driver Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 08/16] drm/amdgpu: Convert driver sysfs attributes to static attributes Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 09/16] drm/amdgpu: Guard against write accesses after device removal Andrey Grodzovsky
2021-05-12 20:17 ` Alex Deucher
2021-05-12 20:30 ` Andrey Grodzovsky
2021-05-12 20:50 ` Alex Deucher
2021-05-13 14:47 ` Andrey Grodzovsky
2021-05-13 14:54 ` Alex Deucher
2021-05-12 14:26 ` [PATCH v7 10/16] drm/sched: Make timeout timer rearm conditional Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 11/16] drm/amdgpu: Prevent any job recoveries after device is unplugged Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 12/16] drm/amdgpu: Fix hang on device removal Andrey Grodzovsky
2021-05-14 14:42 ` Andrey Grodzovsky
2021-05-17 14:40 ` Andrey Grodzovsky
2021-05-17 17:39 ` Alex Deucher
2021-05-17 19:39 ` Christian König
2021-05-17 19:46 ` Andrey Grodzovsky
2021-05-17 19:54 ` Christian König
2021-05-12 14:26 ` [PATCH v7 13/16] drm/scheduler: Fix hang when sched_entity released Andrey Grodzovsky
2021-05-18 14:07 ` Christian König
2021-05-18 15:03 ` Andrey Grodzovsky
2021-05-18 15:15 ` Christian König
2021-05-18 16:17 ` Andrey Grodzovsky
2021-05-18 16:33 ` Christian König
2021-05-18 17:43 ` Andrey Grodzovsky [this message]
2021-05-18 18:02 ` Christian König
2021-05-18 18:09 ` Andrey Grodzovsky
2021-05-18 18:13 ` Christian König
2021-05-18 18:48 ` Andrey Grodzovsky
2021-05-18 20:56 ` Andrey Grodzovsky
2021-05-19 10:57 ` Christian König
2021-05-19 11:03 ` Andrey Grodzovsky
2021-05-19 11:46 ` Christian König
2021-05-19 11:51 ` Andrey Grodzovsky
2021-05-19 11:56 ` Christian König
2021-05-19 14:14 ` [PATCH] drm/sched: Avoid data corruptions Andrey Grodzovsky
2021-05-19 14:15 ` Christian König
2021-05-12 14:26 ` [PATCH v7 14/16] drm/amd/display: Remove superfluous drm_mode_config_cleanup Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 15/16] drm/amdgpu: Verify DMA opearations from device are done Andrey Grodzovsky
2021-05-12 14:26 ` [PATCH v7 16/16] drm/amdgpu: Unmap all MMIO mappings Andrey Grodzovsky
2021-05-14 14:42 ` Andrey Grodzovsky
2021-05-17 14:41 ` Andrey Grodzovsky
2021-05-17 17:43 ` Alex Deucher
2021-05-17 18:46 ` Andrey Grodzovsky
2021-05-17 18:56 ` Alex Deucher
2021-05-17 19:22 ` Andrey Grodzovsky
2021-05-17 19:31 ` [PATCH] " Andrey Grodzovsky
2021-05-18 14:01 ` Andrey Grodzovsky
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