Re: [PATCH 4/6] io_uring: switch normal task_work to a mpscq

[Jens Axboe <axboe@kernel.dk>]

On 6/12/26 12:59 PM, Caleb Sander Mateos wrote:
>> @@ -236,10 +262,14 @@ void io_req_normal_work_add(struct io_kiocb *req)
>>                 return;
>>         }
>>
>> +       /* task_work must only be added once */
>> +       if (test_and_set_bit(0, &tctx->tw_pending))
>> +               return;
> 
> Is tw_pending necessary? How come the task_work_add() exclusivity
> isn't already provided by the mpscq_push() check above?

It is, because the transition from empty -> not-empty no longer works
for that, as the mpscq emtpies one-by-one rather than with a delete-all
kind of primitive.

I missed that originally and things blew up spectacularly very quickly
:-)

-- 
Jens Axboe