Re: [PATCH 0/2] fix hangs with shared sqpoll

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/17/21 2:31 AM, Hillf Danton wrote:
> On Fri, 16 Apr 2021 15:42:07 Pavel Begunkov wrote:
>> On 16/04/2021 15:09, Pavel Begunkov wrote:
>>> On 16/04/2021 14:58, Jens Axboe wrote:
>>>> On 4/16/21 7:12 AM, Pavel Begunkov wrote:
>>>>> On 16/04/2021 14:04, Jens Axboe wrote:
>>>>>> On 4/15/21 6:26 PM, Pavel Begunkov wrote:
>>>>>>> On 16/04/2021 01:22, Pavel Begunkov wrote:
>>>>>>>> Late catched 5.12 bug with nasty hangs. Thanks Jens for a reproducer.
>>>>>>>
>>>>>>> 1/2 is basically a rip off of one of old Jens' patches, but can't
>>>>>>> find it anywhere. If you still have it, especially if it was
>>>>>>> reviewed/etc., may make sense to go with it instead
>>>>>>
>>>>>> I wonder if we can do something like the below instead - we don't
>>>>>> care about a particularly stable count in terms of wakeup
>>>>>> reliance, and it'd save a nasty sync atomic switch.
>>>>>
>>>>> But we care about it being monotonous. There are nuances with it.
>>>>
>>>> Do we, though? We care about it changing when something has happened,
>>>> but not about it being monotonic.
>>>
>>> We may find inflight == get_inflight(), when it's not really so,
>>> and so get to schedule() awhile there are pending requests that
>>> are not going to be cancelled by itself. And those pending requests
>>> may have been non-discoverable and so non-cancellable, e.g. because
>>> were a part of a ling/hardlink.
>>
>> Anyway, there might be other problems because of how wake_up()'s
>> and ctx->refs putting is ordered. Needs to be remade, probably
>> without ctx->refs in the first place.
>>
> Given the test rounds in the current tree, next tree and his tree the

Whose "his" tree?

> percpu count had survived, one of the quick questions is how it fell apart
> last night?

What "percpu count had survived"? Do you mean the percpu-related patch
from the series? What fell apart?

--   
Pavel Begunkov