Re: [PATCH 3/3] io_uring: move struct io_kiocb from task_struct to io_uring_task

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

On 11/3/24 22:18, Jens Axboe wrote:
> On 11/3/24 3:05 PM, Pavel Begunkov wrote:
>> On 11/3/24 21:54, Jens Axboe wrote:
>>> On 11/3/24 2:47 PM, Pavel Begunkov wrote:
>>>> On 11/3/24 17:49, Jens Axboe wrote:
>>>> ...
>>>>> diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
>>>> ...
>>>>>         nd->head = prev_nd->head;
>>>>> @@ -115,7 +115,7 @@ struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
>>>>>         notif->opcode = IORING_OP_NOP;
>>>>>         notif->flags = 0;
>>>>>         notif->file = NULL;
>>>>> -    notif->task = current;
>>>>> +    notif->tctx = current->io_uring;
>>>>>         io_get_task_refs(1);
>>>>>         notif->file_node = NULL;
>>>>>         notif->buf_node = NULL;
>>>>> diff --git a/io_uring/poll.c b/io_uring/poll.c
>>>>> index 7db3010b5733..56332893a4b0 100644
>>>>> --- a/io_uring/poll.c
>>>>> +++ b/io_uring/poll.c
>>>>> @@ -224,8 +224,7 @@ static int io_poll_check_events(struct io_kiocb *req, struct io_tw_state *ts)
>>>>>     {
>>>>>         int v;
>>>>>     -    /* req->task == current here, checking PF_EXITING is safe */
>>>>> -    if (unlikely(req->task->flags & PF_EXITING))
>>>>> +    if (unlikely(current->flags & PF_EXITING))
>>>>>             return -ECANCELED
>>>>
>>>> Unlike what the comment says, req->task doesn't have to match current,
>>>> in which case the new check does nothing and it'll break in many very
>>>> interesting ways.
>>>
>>> In which cases does it not outside of fallback?
>>
>> I think it can only be fallback path
> 
> I think so too, that's what I was getting at. Hence I think we should just
> change these PF_EXITING checks to be PF_KTHREAD instead. If we're invoked
> from that kind of context, cancel.

Replacing with just a PF_KTHREAD check won't be right, you can
get here with the right task but after it has been half killed and
marked PF_EXITING.

-- 
Pavel Begunkov