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

[Jens Axboe <axboe@kernel.dk>]

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...

-- 
Jens Axboe