On Wed, May 17, 2023 at 05:28:33PM +0200, Kevin Wolf wrote:
> nbd_drained_poll() generally runs in the main thread, not whatever
> iothread the NBD server coroutine is meant to run in, so it can't
> directly reenter the coroutines to wake them up.
>
> The code seems to have the right intention, it specifies the correct
> AioContext when it calls qemu_aio_coroutine_enter(). However, this
> functions doesn't schedule the coroutine to run in that AioContext, but
> it assumes it is already called in the home thread of the AioContext.
>
> To fix this, add a new thread-safe qio_channel_wake_read() that can be
> called in the main thread to wake up the coroutine in its AioContext,
> and use this in nbd_drained_poll().
>
> Cc: qemu-sta...@nongnu.org
> Signed-off-by: Kevin Wolf <kw...@redhat.com>
> ---
> include/io/channel.h | 10 ++++++++++
> io/channel.c | 33 +++++++++++++++++++++++++++------
> nbd/server.c | 3 +--
> 3 files changed, 38 insertions(+), 8 deletions(-)
>
Lots of support code...
> +++ b/nbd/server.c
> @@ -1599,8 +1599,7 @@ static bool nbd_drained_poll(void *opaque)
> * enter it here so we don't depend on the client to wake it up.
> */
> if (client->recv_coroutine != NULL && client->read_yielding) {
> - qemu_aio_coroutine_enter(exp->common.ctx,
> - client->recv_coroutine);
> + qio_channel_wake_read(client->ioc);
> }
...for what boils down to a deceptively simple alternative call. But
your reasoning made sense to me, and I can see how your new function
solves the issue.
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
