Re: [PATCH 3/3] io_uring: tweak io_req_task_work_add

[Jens Axboe <axboe@kernel.dk>]

On 6/30/21 4:10 PM, Pavel Begunkov wrote:
> On 6/30/21 10:56 PM, Jens Axboe wrote:
>> On 6/30/21 3:45 PM, Jens Axboe wrote:
>>> On 6/30/21 3:38 PM, Pavel Begunkov wrote:
>>>> On 6/30/21 10:22 PM, Jens Axboe wrote:
>>>>> On 6/30/21 3:19 PM, Pavel Begunkov wrote:
>>>>>> On 6/30/21 10:17 PM, Jens Axboe wrote:
>>>>>>> On 6/30/21 2:54 PM, Pavel Begunkov wrote:
>>>>>>>> Whenever possible we don't want to fallback a request. task_work_add()
>>>>>>>> will be fine if the task is exiting, so don't check for PF_EXITING,
>>>>>>>> there is anyway only a relatively small gap between setting the flag
>>>>>>>> and doing the final task_work_run().
>>>>>>>>
>>>>>>>> Also add likely for the hot path.
>>>>>>>
>>>>>>> I'm not a huge fan of likely/unlikely, and in particular constructs like:
>>>>>>>
>>>>>>>> -	if (test_bit(0, &tctx->task_state) ||
>>>>>>>> +	if (likely(test_bit(0, &tctx->task_state)) ||
>>>>>>>>  	    test_and_set_bit(0, &tctx->task_state))
>>>>>>>>  		return 0;
>>>>>>>
>>>>>>> where the state is combined. In any case, it should be a separate
>>>>>>> change. If there's an "Also" paragraph in a patch, then that's also
>>>>>>> usually a good clue that that particular change should've been
>>>>>>> separate :-)
>>>>>>
>>>>>> Not sure what's wrong with likely above, but how about drop
>>>>>> this one then?
>>>>>
>>>>> Yep I did - we can do the exiting change separately, the commit message
>>>>
>>>> I think 1-2 is good enough for 5.14, I'll just send it for-next
>>>>
>>>>> just needs to be clarified a bit on why it's ok to do now. And that
>>>>
>>>> It should have been ok to do before those 2 patches, but
>>>> haven't tracked where it lost actuality.
>>>
>>> Right, I was thinking it was related to the swapping of the signal
>>> exit and task work run ordering. But didn't look that far yet...
>>
>> BTW, in usual testing, even just the one hunk removing the exit check
>> seems to result in quite a lot of memory leaks running
>> test/poll-mshot-update. So something is funky with the patch.
> 
> I guess you're positive that patches 1-2 have nothing to do
> with that. Right?

I double checked, and seems fine with those two alone. Ran the test
twice, saw massive amounts of leaks with patches 1-3, and none with
patches 1-2 only.

-- 
Jens Axboe