[PATCH] drm/amdgpu: fix sched fence slab teardown

[Christian König]

Reviewed-by: Christian König <christian.koenig at amd.com>

Am 24.10.2016 um 04:34 schrieb zhoucm1:
> Acked-by: Chunming Zhou <david1.zhou at amd.com>
>
> On 2016年10月24日 02:31, Grazvydas Ignotas wrote:
>> To free fences, call_rcu() is used, which calls amd_sched_fence_free()
>> after a grace period. During teardown, there is no guarantee all
>> callbacks have finished, so sched_fence_slab may be destroyed before
>> all fences have been freed. If we are lucky, this results in some slab
>> warnings, if not, we get a crash in one of rcu threads because callback
>> is called after amdgpu has already been unloaded.
>>
>> Fix it with a rcu_barrier().
>>
>> Fixes: 189e0fb76304 ("drm/amdgpu: RCU protected 
>> amd_sched_fence_release")
>> Signed-off-by: Grazvydas Ignotas <notasas at gmail.com>
>> ---
>>   drivers/gpu/drm/amd/scheduler/gpu_scheduler.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c 
>> b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> index 963a24d..910b8d5 100644
>> --- a/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> +++ b/drivers/gpu/drm/amd/scheduler/gpu_scheduler.c
>> @@ -645,6 +645,7 @@ void amd_sched_fini(struct amd_gpu_scheduler *sched)
>>   {
>>       if (sched->thread)
>>           kthread_stop(sched->thread);
>> +    rcu_barrier();
>>       if (atomic_dec_and_test(&sched_fence_slab_ref))
>>           kmem_cache_destroy(sched_fence_slab);
>>   }
>
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