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

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

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.

> 
> 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