Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers

Christian König
2018-08-24T13:28:33Z

Am 24.08.2018 um 15:24 schrieb Michal Hocko:
> On Fri 24-08-18 15:10:08, Christian König wrote:
>> Am 24.08.2018 um 15:01 schrieb Michal Hocko:
>>> On Fri 24-08-18 14:52:26, Christian König wrote:
>>>> Am 24.08.2018 um 14:33 schrieb Michal Hocko:
>>> [...]
>>>>> Thiking about it some more, I can imagine that a notifier callback which
>>>>> performs an allocation might trigger a memory reclaim and that in turn
>>>>> might trigger a notifier to be invoked and recurse. But notifier
>>>>> shouldn't really allocate memory. They are called from deep MM code
>>>>> paths and this would be extremely deadlock prone. Maybe Jerome can come
>>>>> up some more realistic scenario. If not then I would propose to simplify
>>>>> the locking here. We have lockdep to catch self deadlocks and it is
>>>>> always better to handle a specific issue rather than having a code
>>>>> without a clear indication how it can recurse.
>>>> Well I agree that we should probably fix that, but I have some concerns to
>>>> remove the existing workaround.
>>>>
>>>> See we added that to get rid of a real problem in a customer environment and
>>>> I don't want to that to show up again.
>>> It would really help to know more about that case and fix it properly
>>> rather than workaround it like this. Anyway, let me think how to handle
>>> the non-blocking notifier invocation then. I was not able to come up
>>> with anything remotely sane yet.
>> With avoiding allocating memory in the write lock path I don't see an issue
>> any more with that.
>>
>> All what the write lock path does now is adding items to a linked lists,
>> arrays etc....
> Can we change it to non-sleepable lock then?

No, the write side doesn't sleep any more, but the read side does.

See amdgpu_mn_invalidate_node() and that is where you actually need to
handle the non-blocking flag correctly.

Christian.