Re: [PATCH 1/3] drm/amdgpu: Avoid accessing job->entity after the job is scheduled.

[Andrey Grodzovsky <andrey.grodzovsky-5C7GfCeVMHo@public.gmane.org>]

On 2017-10-20 11:59 AM, Andres Rodriguez wrote:
>
>
> On 2017-10-20 09:32 AM, Andrey Grodzovsky wrote:
>> Bug: amdgpu_job_free_cb was accessing s_job->s_entity when the allocated
>> amdgpu_ctx (and the entity inside it) were already deallocated from
>> amdgpu_cs_parser_fini.
>>
>> Fix: Save job's priority on it's creation instead of accessing it from
>> s_entity later on.
>
> I'm not sure if this is the correct approach for a fix.
>
> Keeping s_entity as a dangling pointer could result in a similar bugs 
> being reintroduced. For example, there would still be a race condition 
> between amdgpu_cs_parser_fini() and amdgpu_job_dependency().

.dependency hook is called only in once place amd_sched_entity_pop_job, 
amdgpu_cs_parser_fini will wait  (from amd_sched_entity_fini) for 
wake_up(&sched->job_scheduled) from amd_sched_main so I don't see a race 
here.

>
>
> Instead, it might be better for the job to grab a reference to the 
> context during job_init(), and put that reference on job free.

Originally it was my thinkimg to, but I consulted Christian and he 
advised that quote - "it's not the best idea since
the problem is that when we terminate a process we need to make sure 
that all resources are released or at least not hold for much longer. 
When we keep the ctx alive with the job we need to also keep the VM 
alive and that means we need to keep all the VM page tables alive".

Thanks,
Andrey

>
> Regards,
> Andres
>
>>
>> Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c        |  3 +--
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_job.c       |  5 ++---
>>   drivers/gpu/drm/amd/scheduler/gpu_scheduler.c |  1 +
>>   drivers/gpu/drm/amd/scheduler/gpu_scheduler.h | 32 
>> ++++++++++++---------------
>>   4 files changed, 18 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>> index f7fceb6..a760b6e 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>> @@ -1192,8 +1192,7 @@ static int amdgpu_cs_submit(struct 
>> amdgpu_cs_parser *p,
>>       job->uf_sequence = seq;
>>         amdgpu_job_free_resources(job);
>> -    amdgpu_ring_priority_get(job->ring,
>> - amd_sched_get_job_priority(&job->base));
>> +    amdgpu_ring_priority_get(job->ring, job->base.s_priority);
>>         trace_amdgpu_cs_ioctl(job);
>>       amd_sched_entity_push_job(&job->base);
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> index 0cfc68d..a58e3c5 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> @@ -104,7 +104,7 @@ static void amdgpu_job_free_cb(struct 
>> amd_sched_job *s_job)
>>   {
>>       struct amdgpu_job *job = container_of(s_job, struct amdgpu_job, 
>> base);
>>   -    amdgpu_ring_priority_put(job->ring, 
>> amd_sched_get_job_priority(s_job));
>> +    amdgpu_ring_priority_put(job->ring, s_job->s_priority);
>>       dma_fence_put(job->fence);
>>       amdgpu_sync_free(&job->sync);
>>       amdgpu_sync_free(&job->dep_sync);
>> @@ -141,8 +141,7 @@ int amdgpu_job_submit(struct amdgpu_job *job, 
>> struct amdgpu_ring *ring,
>>       job->fence_ctx = entity->fence_context;
>>       *f = dma_fence_get(&job->base.s_fence->finished);
>>       amdgpu_job_free_resources(job);
>> -    amdgpu_ring_priority_get(job->ring,
>> - amd_sched_get_job_priority(&job->base));
>> +    amdgpu_ring_priority_get(job->ring, job->base.s_priority);
>>       amd_sched_entity_push_job(&job->base);
>>         return 0;
>> diff --git a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c 
>> b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> index e4d3b4e..1bbbce2 100644
>> --- a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> +++ b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> @@ -529,6 +529,7 @@ int amd_sched_job_init(struct amd_sched_job *job,
>>   {
>>       job->sched = sched;
>>       job->s_entity = entity;
>> +    job->s_priority = entity->rq - sched->sched_rq;
>>       job->s_fence = amd_sched_fence_create(entity, owner);
>>       if (!job->s_fence)
>>           return -ENOMEM;
>> diff --git a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h 
>> b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> index 52c8e54..3f75b45 100644
>> --- a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> +++ b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.h
>> @@ -30,6 +30,19 @@
>>   struct amd_gpu_scheduler;
>>   struct amd_sched_rq;
>>   +enum amd_sched_priority {
>> +    AMD_SCHED_PRIORITY_MIN,
>> +    AMD_SCHED_PRIORITY_LOW = AMD_SCHED_PRIORITY_MIN,
>> +    AMD_SCHED_PRIORITY_NORMAL,
>> +    AMD_SCHED_PRIORITY_HIGH_SW,
>> +    AMD_SCHED_PRIORITY_HIGH_HW,
>> +    AMD_SCHED_PRIORITY_KERNEL,
>> +    AMD_SCHED_PRIORITY_MAX,
>> +    AMD_SCHED_PRIORITY_INVALID = -1,
>> +    AMD_SCHED_PRIORITY_UNSET = -2
>> +};
>> +
>> +
>>   /**
>>    * A scheduler entity is a wrapper around a job queue or a group
>>    * of other entities. Entities take turns emitting jobs from their
>> @@ -83,6 +96,7 @@ struct amd_sched_job {
>>       struct delayed_work        work_tdr;
>>       uint64_t            id;
>>       atomic_t karma;
>> +    enum amd_sched_priority s_priority;
>>   };
>>     extern const struct dma_fence_ops amd_sched_fence_ops_scheduled;
>> @@ -114,18 +128,6 @@ struct amd_sched_backend_ops {
>>       void (*free_job)(struct amd_sched_job *sched_job);
>>   };
>>   -enum amd_sched_priority {
>> -    AMD_SCHED_PRIORITY_MIN,
>> -    AMD_SCHED_PRIORITY_LOW = AMD_SCHED_PRIORITY_MIN,
>> -    AMD_SCHED_PRIORITY_NORMAL,
>> -    AMD_SCHED_PRIORITY_HIGH_SW,
>> -    AMD_SCHED_PRIORITY_HIGH_HW,
>> -    AMD_SCHED_PRIORITY_KERNEL,
>> -    AMD_SCHED_PRIORITY_MAX,
>> -    AMD_SCHED_PRIORITY_INVALID = -1,
>> -    AMD_SCHED_PRIORITY_UNSET = -2
>> -};
>> -
>>   /**
>>    * One scheduler is implemented for each hardware ring
>>   */
>> @@ -176,10 +178,4 @@ bool amd_sched_dependency_optimized(struct 
>> dma_fence* fence,
>>                       struct amd_sched_entity *entity);
>>   void amd_sched_job_kickout(struct amd_sched_job *s_job);
>>   -static inline enum amd_sched_priority
>> -amd_sched_get_job_priority(struct amd_sched_job *job)
>> -{
>> -    return (job->s_entity->rq - job->sched->sched_rq);
>> -}
>> -
>>   #endif
>>

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