Re: [PATCH 1/5] io_uring: grab any needed state during defer prep

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

On 02/10/2020 19:14, Pavel Begunkov wrote:
> On 19/09/2020 19:56, Pavel Begunkov wrote:
>> On 19/09/2020 18:27, Pavel Begunkov wrote:
>>> On 14/09/2020 19:25, Jens Axboe wrote:
>>>> Always grab work environment for deferred links. The assumption that we
>>>> will be running it always from the task in question is false, as exiting
>>>> tasks may mean that we're deferring this one to a thread helper. And at
>>>> that point it's too late to grab the work environment.
>> Forgot that they will be cancelled there. So, how it could happen?
>> Is that the initial thread will run task_work but loosing
>> some resources like mm prior to that? e.g. in do_exit()
> 
> Jens, please let me know when you get time for that. I was thinking that
> you were meaning do_exit(), which does task_work_run() after killing mm,
> etc., but you mentioned a thread helper in the description... Which one
> do you mean?

Either it refers to stuff after io_ring_ctx_wait_and_kill(), which
delegates the rest to io_ring_exit_work() via @system_unbound_wq.

> 
>>
>>>
>>>>
>>>> Fixes: debb85f496c9 ("io_uring: factor out grab_env() from defer_prep()")
>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>> ---
>>>>  fs/io_uring.c | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>> index 175fb647d099..be9d628e7854 100644
>>>> --- a/fs/io_uring.c
>>>> +++ b/fs/io_uring.c
>>>> @@ -5449,6 +5449,8 @@ static int io_req_defer_prep(struct io_kiocb *req,
>>>>  	if (unlikely(ret))
>>>>  		return ret;
>>>>  
>>>> +	io_prep_async_work(req);
>>>> +
>>>>  	switch (req->opcode) {
>>>>  	case IORING_OP_NOP:
>>>>  		break;
>>>>
>>>
>>
> 

-- 
Pavel Begunkov