[PATCH] drm/amdgpu: fix fence slab teardown

[Christian König]

Interesting catch, patch is 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 amdgpu_fence_free()
>> after a grace period. During teardown, there is no guarantee all
>> callbacks have finished, so amdgpu_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: b44135351a3a ("drm/amdgpu: RCU protected amdgpu_fence_release")
>> Signed-off-by: Grazvydas Ignotas <notasas at gmail.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> index 3a2e42f..77b34ec 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> @@ -68,6 +68,7 @@ int amdgpu_fence_slab_init(void)
>>     void amdgpu_fence_slab_fini(void)
>>   {
>> +    rcu_barrier();
>>       kmem_cache_destroy(amdgpu_fence_slab);
>>   }
>>   /*
>
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