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SubjectRe: WARNING in __mmdrop
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On 2019/7/26 下午11:03, Jason Gunthorpe wrote:
> On Fri, Jul 26, 2019 at 10:00:20PM +0800, Jason Wang wrote:
>> The question is, MMU notifier are allowed to be blocked on
>> invalidate_range_start() which could be much slower than synchronize_rcu()
>> to finish.
>>
>> Looking at amdgpu_mn_invalidate_range_start_gfx() which calls
>> amdgpu_mn_invalidate_node() which did:
>>
>>                 r = reservation_object_wait_timeout_rcu(bo->tbo.resv,
>>                         true, false, MAX_SCHEDULE_TIMEOUT);
>>
>> ...
> The general guidance has been that invalidate_start should block
> minimally, if at all.
>
> I would say synchronize_rcu is outside that guidance.


Yes, I get this.


>
> BTW, always returning EAGAIN for mmu_notifier_range_blockable() is not
> good either, it should instead only return EAGAIN if any
> vhost_map_range_overlap() is true.


Right, let me optimize that.

Thanks


>
> Jason

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