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

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

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.
> 
> That's a shame. Do you mean that's from lines like below?
> 
> int io_async_buf_func()
> {
>     ...
>     if (!io_req_task_work_add()) {
>         ...
>         tsk = io_wq_get_task(req->ctx->io_wq);
>         task_work_add(tsk, &req->task_work, 0);
>     }
> }
> 
> It looks like failing such requests would be a better option.
> io_uring_flush() would want them killed for PF_EXITING processes anyway.

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()

> 
>>
>> 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