[PATCH 3/3] drm/amdgpu: Fix deadlock during GPU reset.
Liu, Monk
Monk.Liu at amd.com
Mon Oct 23 07:38:46 UTC 2017
Let's make it clear enough:
> That won't work. All VM updates must be completed while the reservation object lock is still held, otherwise you run into possible concurrent VM updates.
All VM updates will be represented as fence which will be hook in the sync object, and after we push job to scheduler, we immediately call ttm_eu_fence_buffer_objects()
So that means the reservation object lock is *not* hold anymore, right ? but keep in mind that this point scheduler may not even begin to work, so I don't believe
This sentence " All VM updates must be completed while the reservation object lock is still held"
> No, TTM callbacks into our driver to do the move. So we don't have an opportunity to drop the reservation lock.
For TTM callbacks, can you help illustrate how the deadlock triggered ???
BR Monk
-----Original Message-----
From: Christian König [mailto:ckoenig.leichtzumerken at gmail.com]
Sent: 2017年10月23日 15:31
To: Liu, Monk <Monk.Liu at amd.com>; Koenig, Christian <Christian.Koenig at amd.com>; Grodzovsky, Andrey <Andrey.Grodzovsky at amd.com>; amd-gfx at lists.freedesktop.org
Subject: Re: [PATCH 3/3] drm/amdgpu: Fix deadlock during GPU reset.
> For VM updates, the situation is same as commands submission, deadlock
> can also be solved by moving ttm_eu_fence_buffer_objects() ahead of
> push_job()
That won't work. All VM updates must be completed while the reservation object lock is still held, otherwise you run into possible concurrent VM updates.
Keep in mind that you can have multiple context per VM, so that isn't covered by the per context lock.
> For TTM buffers moves can we pardon gpu_reset routine and wait till the TTM moves complete ?
No, TTM callbacks into our driver to do the move. So we don't have an opportunity to drop the reservation lock.
Additional to that kfifo has some other drawbacks as well. For example we waste around 20k of memory for each context for multi media ring buffers which are mostly unused.
Regards,
Christian.
Am 23.10.2017 um 09:24 schrieb Liu, Monk:
> For VM updates, the situation is same as commands submission, deadlock
> can also be solved by moving ttm_eu_fence_buffer_objects() ahead of push_job() For TTM buffers moves can we pardon gpu_reset routine and wait till the TTM moves complete ?
>
> -----Original Message-----
> From: Christian König [mailto:ckoenig.leichtzumerken at gmail.com]
> Sent: 2017年10月23日 15:09
> To: Liu, Monk <Monk.Liu at amd.com>; Grodzovsky, Andrey
> <Andrey.Grodzovsky at amd.com>; amd-gfx at lists.freedesktop.org
> Cc: Koenig, Christian <Christian.Koenig at amd.com>
> Subject: Re: [PATCH 3/3] drm/amdgpu: Fix deadlock during GPU reset.
>
> We discussed that as well, problem is that this won't be sufficient.
>
> We push to the kfifo not only during command submission, but also for VM updates and TTM buffers moves.
>
> So we can still deadlock because of them.
>
> Regards,
> Christian.
>
> Am 23.10.2017 um 05:03 schrieb Liu, Monk:
>> Why not use a more simple way ?
>>
>> Like moving ttm_eu_fence_buffer_objects() to before amd_sched_entity_push_job() ?
>> That could solve the deadlock from your description
>>
>> And the push order is already guaranteed by context->mutex (which is
>> also a patch from you)
>>
>>
>> BR Monk
>>
>> -----Original Message-----
>> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On
>> Behalf Of Andrey Grodzovsky
>> Sent: 2017年10月20日 21:32
>> To: amd-gfx at lists.freedesktop.org
>> Cc: Grodzovsky, Andrey <Andrey.Grodzovsky at amd.com>; Koenig, Christian
>> <Christian.Koenig at amd.com>
>> Subject: [PATCH 3/3] drm/amdgpu: Fix deadlock during GPU reset.
>>
>> Switch from kfifo to SPSC queue.
>>
>> Bug:
>> Kfifo is limited at size, during GPU reset it would fill up to limit and the pushing thread (producer) would wait for the scheduler worker to consume the items in the fifo while holding reservation lock on a BO. The gpu reset thread on the other hand blocks the scheduler during reset. Before it unblocks the sceduler it might want to recover VRAM and so will try to reserve the same BO the producer thread is already holding creating a deadlock.
>>
>> Fix:
>> Switch from kfifo to SPSC queue which is unlimited in size.
>>
>> Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky at amd.com>
>> ---
>> drivers/gpu/drm/amd/scheduler/gpu_sched_trace.h | 4 +-
>> drivers/gpu/drm/amd/scheduler/gpu_scheduler.c | 51 ++++++++++---------------
>> drivers/gpu/drm/amd/scheduler/gpu_scheduler.h | 4 +-
>> 3 files changed, 26 insertions(+), 33 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/scheduler/gpu_sched_trace.h
>> b/drivers/gpu/drm/amd/scheduler/gpu_sched_trace.h
>> index 8bd3810..86838a8 100644
>> --- a/drivers/gpu/drm/amd/scheduler/gpu_sched_trace.h
>> +++ b/drivers/gpu/drm/amd/scheduler/gpu_sched_trace.h
>> @@ -28,8 +28,8 @@ TRACE_EVENT(amd_sched_job,
>> __entry->id = sched_job->id;
>> __entry->fence = &sched_job->s_fence->finished;
>> __entry->name = sched_job->sched->name;
>> - __entry->job_count = kfifo_len(
>> - &sched_job->s_entity->job_queue) / sizeof(sched_job);
>> + __entry->job_count = spsc_queue_count(
>> + &sched_job->s_entity->job_queue);
>> __entry->hw_job_count = atomic_read(
>> &sched_job->sched->hw_rq_count);
>> ),
>> diff --git a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> index 1bbbce2..0c9cdc0 100644
>> --- a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> +++ b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> @@ -28,9 +28,14 @@
>> #include <drm/drmP.h>
>> #include "gpu_scheduler.h"
>>
>> +#include "spsc_queue.h"
>> +
>> #define CREATE_TRACE_POINTS
>> #include "gpu_sched_trace.h"
>>
>> +#define to_amd_sched_job(sched_job) \
>> + container_of((sched_job), struct amd_sched_job, queue_node)
>> +
>> static bool amd_sched_entity_is_ready(struct amd_sched_entity *entity); static void amd_sched_wakeup(struct amd_gpu_scheduler *sched); static void amd_sched_process_job(struct dma_fence *f, struct dma_fence_cb *cb); @@ -123,8 +128,6 @@ int amd_sched_entity_init(struct amd_gpu_scheduler *sched,
>> struct amd_sched_rq *rq,
>> uint32_t jobs)
>> {
>> - int r;
>> -
>> if (!(sched && entity && rq))
>> return -EINVAL;
>>
>> @@ -135,9 +138,7 @@ int amd_sched_entity_init(struct
>> amd_gpu_scheduler *sched,
>>
>> spin_lock_init(&entity->rq_lock);
>> spin_lock_init(&entity->queue_lock);
>> - r = kfifo_alloc(&entity->job_queue, jobs * sizeof(void *), GFP_KERNEL);
>> - if (r)
>> - return r;
>> + spsc_queue_init(&entity->job_queue);
>>
>> atomic_set(&entity->fence_seq, 0);
>> entity->fence_context = dma_fence_context_alloc(2); @@ -170,7 +171,7 @@ static bool amd_sched_entity_is_initialized(struct amd_gpu_scheduler *sched, static bool amd_sched_entity_is_idle(struct amd_sched_entity *entity) {
>> rmb();
>> - if (kfifo_is_empty(&entity->job_queue))
>> + if (spsc_queue_peek(&entity->job_queue) == NULL)
>> return true;
>>
>> return false;
>> @@ -185,7 +186,7 @@ static bool amd_sched_entity_is_idle(struct amd_sched_entity *entity)
>> */
>> static bool amd_sched_entity_is_ready(struct amd_sched_entity *entity) {
>> - if (kfifo_is_empty(&entity->job_queue))
>> + if (spsc_queue_peek(&entity->job_queue) == NULL)
>> return false;
>>
>> if (ACCESS_ONCE(entity->dependency)) @@ -227,7 +228,7 @@ void
>> amd_sched_entity_fini(struct amd_gpu_scheduler *sched,
>> */
>> kthread_park(sched->thread);
>> kthread_unpark(sched->thread);
>> - while (kfifo_out(&entity->job_queue, &job, sizeof(job))) {
>> + while ((job =
>> +to_amd_sched_job(spsc_queue_pop(&entity->job_queue))))
>> +{
>> struct amd_sched_fence *s_fence = job->s_fence;
>> amd_sched_fence_scheduled(s_fence);
>> dma_fence_set_error(&s_fence->finished, -ESRCH); @@ -235,9 +236,7 @@ void amd_sched_entity_fini(struct amd_gpu_scheduler *sched,
>> dma_fence_put(&s_fence->finished);
>> sched->ops->free_job(job);
>> }
>> -
>> }
>> - kfifo_free(&entity->job_queue);
>> }
>>
>> static void amd_sched_entity_wakeup(struct dma_fence *f, struct
>> dma_fence_cb *cb) @@ -332,18 +331,21 @@ static bool
>> amd_sched_entity_add_dependency_cb(struct amd_sched_entity *entity)
>> }
>>
>> static struct amd_sched_job *
>> -amd_sched_entity_peek_job(struct amd_sched_entity *entity)
>> +amd_sched_entity_pop_job(struct amd_sched_entity *entity)
>> {
>> struct amd_gpu_scheduler *sched = entity->sched;
>> - struct amd_sched_job *sched_job;
>> + struct amd_sched_job *sched_job = to_amd_sched_job(
>> + spsc_queue_peek(&entity->job_queue));
>>
>> - if (!kfifo_out_peek(&entity->job_queue, &sched_job, sizeof(sched_job)))
>> + if (!sched_job)
>> return NULL;
>>
>> while ((entity->dependency = sched->ops->dependency(sched_job)))
>> if (amd_sched_entity_add_dependency_cb(entity))
>> return NULL;
>>
>> + sched_job->s_entity = NULL;
>> + spsc_queue_pop(&entity->job_queue);
>> return sched_job;
>> }
>>
>> @@ -354,18 +356,14 @@ amd_sched_entity_peek_job(struct amd_sched_entity *entity)
>> *
>> * Returns true if we could submit the job.
>> */
>> -static bool amd_sched_entity_in(struct amd_sched_job *sched_job)
>> +static void amd_sched_entity_in(struct amd_sched_job *sched_job)
>> {
>> struct amd_gpu_scheduler *sched = sched_job->sched;
>> struct amd_sched_entity *entity = sched_job->s_entity;
>> - bool added, first = false;
>> + bool first = false;
>>
>> spin_lock(&entity->queue_lock);
>> - added = kfifo_in(&entity->job_queue, &sched_job,
>> - sizeof(sched_job)) == sizeof(sched_job);
>> -
>> - if (added && kfifo_len(&entity->job_queue) == sizeof(sched_job))
>> - first = true;
>> + first = spsc_queue_push(&entity->job_queue,
>> +&sched_job->queue_node);
>>
>> spin_unlock(&entity->queue_lock);
>>
>> @@ -377,7 +375,6 @@ static bool amd_sched_entity_in(struct amd_sched_job *sched_job)
>> spin_unlock(&entity->rq_lock);
>> amd_sched_wakeup(sched);
>> }
>> - return added;
>> }
>>
>> /* job_finish is called after hw fence signaled @@ -514,11 +511,8 @@ void amd_sched_job_recovery(struct amd_gpu_scheduler *sched)
>> */
>> void amd_sched_entity_push_job(struct amd_sched_job *sched_job) {
>> - struct amd_sched_entity *entity = sched_job->s_entity;
>> -
>> trace_amd_sched_job(sched_job);
>> - wait_event(entity->sched->job_scheduled,
>> - amd_sched_entity_in(sched_job));
>> + amd_sched_entity_in(sched_job);
>> }
>>
>> /* init a sched_job with basic field */ @@ -611,7 +605,7 @@ static int amd_sched_main(void *param) {
>> struct sched_param sparam = {.sched_priority = 1};
>> struct amd_gpu_scheduler *sched = (struct amd_gpu_scheduler *)param;
>> - int r, count;
>> + int r;
>>
>> sched_setscheduler(current, SCHED_FIFO, &sparam);
>>
>> @@ -629,7 +623,7 @@ static int amd_sched_main(void *param)
>> if (!entity)
>> continue;
>>
>> - sched_job = amd_sched_entity_peek_job(entity);
>> + sched_job = amd_sched_entity_pop_job(entity);
>> if (!sched_job)
>> continue;
>>
>> @@ -656,9 +650,6 @@ static int amd_sched_main(void *param)
>> amd_sched_process_job(NULL, &s_fence->cb);
>> }
>>
>> - count = kfifo_out(&entity->job_queue, &sched_job,
>> - sizeof(sched_job));
>> - WARN_ON(count != sizeof(sched_job));
>> wake_up(&sched->job_scheduled);
>> }
>> return 0;
>> diff --git a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> index 3f75b45..8844ce7 100644
>> --- a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> +++ b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> @@ -26,6 +26,7 @@
>>
>> #include <linux/kfifo.h>
>> #include <linux/dma-fence.h>
>> +#include "spsc_queue.h"
>>
>> struct amd_gpu_scheduler;
>> struct amd_sched_rq;
>> @@ -56,7 +57,7 @@ struct amd_sched_entity {
>> struct amd_gpu_scheduler *sched;
>>
>> spinlock_t queue_lock;
>> - struct kfifo job_queue;
>> + struct spsc_queue job_queue;
>>
>> atomic_t fence_seq;
>> uint64_t fence_context;
>> @@ -87,6 +88,7 @@ struct amd_sched_fence { };
>>
>> struct amd_sched_job {
>> + struct spsc_node queue_node;
>> struct amd_gpu_scheduler *sched;
>> struct amd_sched_entity *s_entity;
>> struct amd_sched_fence *s_fence;
>> --
>> 2.7.4
>>
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