On 2/23/21 7:30 PM, Xiaoguang Wang wrote: > hi Pavel, > >> On 08/02/2021 13:35, Pavel Begunkov wrote: >>> On 08/02/2021 02:50, Xiaoguang Wang wrote: >>>>>> The io_identity's count is underflowed. It's because in io_put_identity, >>>>>> first argument tctx comes from req->task->io_uring, the second argument >>>>>> comes from the task context that calls io_req_init_async, so the compare >>>>>> in io_put_identity maybe meaningless. See below case: >>>>>> task context A issue one polled req, then req->task = A. >>>>>> task context B do iopoll, above req returns with EAGAIN error. >>>>>> task context B re-issue req, call io_queue_async_work for req. >>>>>> req->task->io_uring will set to task context B's identity, or cow new one. >>>>>> then for above case, in io_put_identity(), the compare is meaningless. >>>>>> >>>>>> IIUC, req->task should indicates the initial task context that issues req, >>>>>> then if it gets EAGAIN error, we'll call io_prep_async_work() in req->task >>>>>> context, but iopoll reqs seems special, they maybe issued successfully and >>>>>> got re-issued in other task context because of EAGAIN error. >>>>> >>>>> Looks as you say, but the patch doesn't solve the issue completely. >>>>> 1. We must not do io_queue_async_work() under a different task context, >>>>> because of it potentially uses a different set of resources. So, I just >>>>> thought that it would be better to punt it to the right task context >>>>> via task_work. But... >>>>> >>>>> 2. ...iovec import from io_resubmit_prep() might happen after submit ends, >>>>> i.e. when iovec was freed in userspace. And that's not great at all. >>>> Yes, agree, that's why I say we neeed to re-consider the io identity codes >>>> more in commit message :) I'll have a try to prepare a better one. >>> >>> I'd vote for dragging -AGAIN'ed reqs that don't need io_import_iovec() >>> through task_work for resubmission, and fail everything else. Not great, >>> but imho better than always setting async_data. >> >> Hey Xiaoguang, are you working on this? I would like to leave it to you, >> If you do. > Sorry, currently I'm busy with other project and don't have much time to work on > it yet. Hao Xu will help to continue work on the new version patch. Is it issue or reissue? I found this one today: https://lore.kernel.org/io-uring/c9f6e1f6-ff82-0e58-ab66-956d0cde30ff@xxxxxxxxx/ -- Jens Axboe
