On 1/28/19 6:29 PM, Jann Horn wrote:
> On Mon, Jan 28, 2019 at 10:35 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
>> The submission queue (SQ) and completion queue (CQ) rings are shared
>> between the application and the kernel. This eliminates the need to
>> copy data back and forth to submit and complete IO.
> [...]
>> +static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
>> +{
>> + struct io_kiocb *req;
>> +
>> + /* safe to use the non tryget, as we're inside ring ref already */
>> + percpu_ref_get(&ctx->refs);
>
> Is that true? In the path io_sq_thread() -> io_submit_sqes() ->
> io_submit_sqe() -> io_get_req(), I don't see anything that's already
> holding a reference for you. Is the worker thread holding a reference
> somewhere that I'm missing?
If the thread is alive, then the ctx is alive. Before we drop the last
ref to the ctx (and kill it), we wait for the thread to exit.
--
Jens Axboe
