Am 11.07.2019 um 21:58 hat Max Reitz geschrieben:
> When nbd_close() is called from a coroutine, the connection_co never
> gets to run, and thus nbd_teardown_connection() hangs.
>
> This is because aio_co_enter() only puts the connection_co into the main
> coroutine's wake-up queue, so this main coroutine needs to yield and
> reschedule itself to let the connection_co run.
>
> Signed-off-by: Max Reitz <[email protected]>
> ---
> block/nbd.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/block/nbd.c b/block/nbd.c
> index 81edabbf35..b83b6cd43e 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -135,7 +135,17 @@ static void nbd_teardown_connection(BlockDriverState *bs)
> qio_channel_shutdown(s->ioc,
> QIO_CHANNEL_SHUTDOWN_BOTH,
> NULL);
> - BDRV_POLL_WHILE(bs, s->connection_co);
> +
> + if (qemu_in_coroutine()) {
> + /* Let our caller poll and just yield until connection_co is done */
> + while (s->connection_co) {
> + aio_co_schedule(qemu_get_current_aio_context(),
> + qemu_coroutine_self());
> + qemu_coroutine_yield();
> + }
Isn't this busy waiting? Why not let s->connection_co wake us up when
it's about to terminate instead of immediately rescheduling ourselves?
> + } else {
> + BDRV_POLL_WHILE(bs, s->connection_co);
> + }
>
> nbd_client_detach_aio_context(bs);
> object_unref(OBJECT(s->sioc));
Kevin
